Tag: marine invertebrates

Now you see it, now you don’t

Posted on by Allison J. Gong

This morning in the intertidal I was reminded of how often I encounter animals I wasn’t looking for and almost missed seeing at all. That got me thinking about color and pattern in the intertidal, and how they can be used either to be seen or to avoid being seen. Some critters–the nudibranchs immediately come to mind–are so brightly colored that they are impossible to miss, while others are camouflaged to the point that it takes a trained eye to see them.

Truth be told, however, most of the animals in the intertidal don’t have eyes, or at least eyes that can form images the way ours do. While just about any animal might be preyed upon by birds at low tide, most of the predators a creature of the tidepools might face would not be visual predators. This in turn begs the question of just how adaptive or not a species’ crypticness is. The way I see it, there are three options, or hypotheses about the potential benefit of an animal’s coloration and patterning:

  1. Colors and patterns that make an animal conspicuous are advantageous.
  2. Colors and patterns that make an animal cryptic or camouflaged are advantageous.
  3. Colors and patterns are neither advantageous or disadvantageous.

Today I’m going to consider hypothesis #2, as it is the most interesting one. Let’s put aside for now the question of how an animal’s color comes to be and consider only its effect on visibility to Homo sapiens (specifically, me).

Example #1 (obvious): Tonicella chitons

These are the pink chitons that I find on exposed coasts. They eat encrusting coralline algae, and I suspect their color derives at least in part from their diet. Here’s one that perfectly matches its food:

The chiton Tonicella lokii at Pistachio Beach
29 May 2017
© Allison J. Gong

On the other hand, Tonicella isn’t always this entirely pink, nor is it always seen on coralline algae:

The chiton Tonicella lokii at Pistachio Beach
29 May 2017
© Allison J. Gong
The chiton Tonicella lokii at Monastery Beach
27 October 2015
© Allison J. Gong

The chiton I saw at Monastery Beach wasn’t anywhere near coralline algae. It has obviously been eating something, probably algal films of whatever sort it comes across. Correlation is not causation, but it may not be mere coincidence that this pale version of Tonicella lokii lives on rock devoid of coralline algae.

Example #2 (obvious): Decorator crabs

Tonicella doesn’t intentionally alter its appearance by eating pink food. Given the extremely rudimentary nature of a chiton’s nervous system, it likely can’t intentionally do much of anything. It doesn’t have eyes so it cannot see, although there are light-sensing organs called aesthetes in the dorsal shell plates and light-sensitive cells in the lateral girdle. Chitons make their way through the world largely by following chemical gradients, either in the water current or on the substrate.

Crabs, on the other hand, have very complex compound eyes and can, to some extent, see what’s going on around them. The compound eyes of arthropods are highly effective motion sensors, certainly much more sensitive than our eyes are, which is why it’s so hard to sneak up on a fly even if you’re extending your reach by using a fly swatter. Crabs certainly are aware of the visual aspects of their surroundings. They can see potential threats and typically respond in one of three ways: (1) scuttling away; (2) coming out fighting; and (3) remaining still and trying not to be noticed.

It takes energy to scuttle back and forth, and the little shore crabs (Pachygrapsus crassipes) are always on the move. They are quick to run for cover when approached, but will come out and resume their explorations if you sit still for about a minute. They are really fast and difficult to catch, perhaps not quite as challenging as the Sally Lightfoot crabs that so enraged the crew of the Western Flyer during Ed Ricketts’ and John Steinbeck’s excursion to the Sea of Cortez, but hard enough to be not worth my effort. Fighting is an option only for those equipped to fight. Rock crabs (for example, Romaleon antennarium) remain hidden under algae or partially buried in sand, but when exposed they come out with big claws open and ready to pinch the hell out of anything that comes close. These are the only animals that I really worry could hurt me in the intertidal.

Which leaves the hold-still-and-hope-not-to-be-seen option. This is what decorator crabs do. In terms of temperament, decorator crabs (of which there are several species) are placid and unaggressive: they will pinch when provoked and it can hurt, but they won’t do the kind of damage that a rock crab would happily inflict. Decorator crabs hide in plain sight by covering their carapace and legs with little bits of the environment, usually algae. A well-decorated crab can be sporting several species of algae on its back.

This morning I saw and collected this small crab:

A small decorator crab, Pugettia richii, on a bed of Egregia menziesii at Davenport Landing
11 July 2017
© Allison J. Gong

I actually didn’t see it at first. I was pawing through the thick algal growth and felt its little feet scratching my hand. I peeked under the algae and there was the crab. Its carapace is about 2.5 cm across, and its claws probably wouldn’t be able to pinch human skin even if the crab tried to. Which it certainly didn’t. I wanted to observe the crab more closely in and keep it for use when I teach the crustacean diversity lab this fall, so I brought it back to be examined under the dissecting scope.

A decorated Pugettia richii, observed in the lab
11 July 201
© Allison J. Gong

The crab’s own color is a dark brownish red, which helps it hide amongst the red algae. It adds to the environment-as-appearance effect by attaching at least three species of red algae to its carapace. The crab does this by grabbing a piece of algae with one of its claws, then reaching up and behind its head to put it on the carapace, which has has tiny hooks that hang onto the decoration. It’s a very nifty scheme, but there’s one big problem. Each time the crab molts it loses its decoration and has to acquire its accessories all over again.

Example #3 (not obvious at all): Lottia digitalis

We have about a gazillion species of limpets on the California coast. Well, not really but it certainly does feel like it. To make things even more difficult I can’t seem to keep the current scientific names straight. I know that many of the commonly encountered intertidal limpets have been consolidated into the genus Lottia (this includes species that I learned by another name way back when) and I’m slowly getting used to recognizing the Lottia “look”. However, aside from the owl limpet (L. gigantea), which is much bigger and more conspicuous than any others, the other species are difficult to distinguish and I can never remember if species x has the deep ridges or if that’s species y. Ugh.

Earlier this spring I was in the field with my friend Brenna, and she was showing me the differences between Lottia scabra and L. digitalis. Brenna studies molluscs so I know she knows what she’s talking about. Lottia scabra is now easy for me to recognize, but L. digitalis is both trickier and more interesting.

Limpets Lottia scabra (upper right) and L. digitalis (left and lower right) among barnacles at Natural Bridges
25 June 2017
© Allison J. Gong

See how those all look like limpets? Now look at this:

Davenport Landing
11 July 2017
© Allison J. Gong

Do you even see the limpets?

The large animals in the photo are gooseneck barnacles, Pollicipes polymerus. They live on and amongst mussels in the mid-intertidal. This spring Brenna told me that Lottia digitalis comes in a morph that lives on and looks like Pollicipes. I’d never seen it until today. Look at the photo again. Can you see the limpets now?

Here are some more photos.

Lottia digitalis (“Pollicipes morph”) at Natural Bridges
11 July 2017
© Allison J. Gong
Lottia digitalis (“Pollicipes morph”) at Natural Bridges
11 July 2017
© Allison J. Gong

Isn’t it remarkable how these limpets have exactly the colors and pattern as the plates of Pollicipes? And I didn’t even know about them six months ago. I love having new things to learn and more reasons to pay closer attention to creatures I tend to take for granted. I think it’s time for me to tackle the challenge of identifying limpets in the field. Next season, that is. Today was probably my last day in the intertidal for a few months. We won’t have decent low tides during daylight hours until November.

Peanut worms!

Posted on by Allison J. Gong

If I ask my invertebrate zoology students to name three characteristics of the Phylum Annelida, they would dutifully include segmentation and chaetae (bristles) in the list. And they would be correct. Annelids, for the most part, are segmented and many of them have chaetae. But in biology there are many exceptions for every rule we teach, and it’s these exceptions that make a deeper study of biology so rewarding.

Peanut worms (Phascolosoma agassizii) at Pigeon Point
30 April 2017
© Allison J. Gong

A couple of weeks ago I did some collecting in the intertidal at Pigeon Point. It was a very accommodating low tide, and I had a lot of time to poke around and explore. I found an area that had several decently sized rocks that I could turn over, and had fun seeing what lives on the side away from the light. Some of the animals on the underside of rocks are the common ones you see everywhere–turban snails, limpets, Leptasterias stars, and the like. Some, however, prefer a life of darkness and actively move away from the sun when their rock is turned over. And others happen to live in the sand under the rock and might not care one way or the other about the light.

Peanut worms, scientifically known as sipunculans, are delightful small worms that in my opinion are vastly underappreciated. This is understandable, as they are usually hidden in sand or rubble and aren’t exactly conspicuous even when uncovered. Phascolosoma agassizii is our local sipunculan. Like all sipunculans it is unsegmented, and it has no chaetae. Peanut worms used to be elevated to their own phylum, the Phylum Sipuncula; however, molecular evidence shows that they are indeed annelids despite their apparent loss of key features such as body segmentation and chaetae.

Peanut worms (Phascolosoma agassizii) at Pigeon Point
30 April 2017
© Allison J. Gong

They do look vaguely peanut-ish, don’t they? They’re small, maybe 6 cm all stretched out, which you hardly ever see. Phascolosoma agassizii is a grayish pink color, with irregular black stripes that usually don’t form complete hoops around the body. Peanut worms are sedentary, living with most of the body buried in sand, rubble, shell debris, kelp holdfasts, etc. One of the weird things about them is that the mouth in located on the distal end of a long tube called the introvert. Most of the time the introvert is stuffed inside the main body region, or trunk. It is eversible and unrolls from the inside out, sort of like when you remove a long sock by pulling the top edge down over your leg and off your foot. The mouth on the end of the introvert is surrounded by short sticky tentacles, and the introvert dabs around to pick up organic deposits from the surfaces. Mucus and cilia on the tentacles convey the yummy organic gunk to the mouth, and a pharynx pushes food through to a long esophagus that runs the length of the introvert and leads to the long coiled intestine in the trunk.

Watch these peanut worms extending and retracting their introverts. Cute, aren’t they?

I brought three peanut worms back to the lab with me, where they are happily living in my sand tank. Their housemates are ~15 sand crabs (Emerita analoga) and a clump of tube-dwelling polychaetes (Phragmatopoma californica). I never see them unless I dig them up from the sand, which leads me to believe that they do most of their feeding at night. Either that or they actually do actively shy away from the light.

Despite not sharing much in the way of apparent morphological similarity with more typical annelids, sipunculans are indeed annelid-like in other ways. Many of their internal structures are like those of annelids, and at least their early development (cleavage pattern and differentiation of tissue layers) follows the annelidan pathway. The species that have indirect development have a trochophore larva, typical of the marine annelids, that in some cases morphs into a second larval stage called a pelagosphera.

Sipunculans are the poster child for Animals That Are Not What They Seem. But they are interesting in their own way, and I always have a “yay!” moment when I find them in the field. It’s really hard not to make sound effects as they’re rolling their introverts in and out. You should try it yourself some time.

Eight is enough

Posted on by Allison J. Gong

One of the defining characteristics of the Phylum Mollusca is the possession of a shell, which serves both as a protective covering and an exoskeleton. We’ve all seen snails, and some people may have noticed that snails often withdraw entirely into their shells and even have a little door that they can use to seal up the opening of the shell. That little door is called the operculum. Opercula occur in non-molluscan animals, too, such as some of the tube-dwelling polychaete worms and some of the thecate hydroids. Snail opercula come in lots of different shapes, depending on the aperture of their owner’s shell.

Calliostoma ligatum at Mitchell’s Cove
2 April 2017
© Allison J. Gong

Given the enormous morphological diversity within the Mollusca it shouldn’t be surprising that their shells vary immensely in prominence and shape. In fact, molluscan shells demonstrate quite beautifully the relationship between form and function. The benthic and most familiar molluscs, the gastropod snails, generally have coiled shells. Notable exceptions to this generality are the marine opisthobranchs (nudibranchs and sea hares) and the terrestrial slugs. And for the most part snail shells look recognizably like snail shells, even though some are plain coils, others may be flattened (e.g., abalones), and still others may be crazily ornamented. Aquatic animals crawl around in water, which helps to support the weight of heavily calcified shells. Terrestrial snails, on the other hand, live in a much less dense medium (air) and have lighter, less calcified shells. The trade-off for a more easily transportable shell is that air is also very drying, and a thinner shell provides less protection from desiccation.

I should state for the record right now that I’m not talking about the many molluscs that don’t have shells at all, or that have much reduced shells.

View into the exhalant opening of a mussel (Mytilus sp.) at the Santa Cruz Yacht Harbor
29 August 2015
© Allison J. Gong

The bivalve molluscs (mussels, clams, oysters, etc.) live inside a pair of shells. They are sedentary animals, living either attached to a hard surface or buried in sand or mud. Not being able to run from predators (although some scallops can swim!), their only defense is the toughness of their shells and the strength of the adductor muscles that hold the shells closed. Most bivalves feed by sucking water into the shells through an incurrent siphon, using their gills to filter food particles from the water, and expelling the water through an excurrent siphon. To do so they must open their shells enough to extend their siphons, or at least expose inhalant and exhalant openings, to the water current surrounding them.

So, snails have one shell and bivalves have two. Some of the most interesting molluscs, in terms of shell morphology, are the chitons. The Polyplacophora (Gk: ‘many plate bearer’) have a shell that is divided into eight dorsal plates. This makes them immediately distinguishable from just about any other animal.

Chiton (Lepidozona mertensii) at Point Piños
6 February 2016
© Allison J. Gong

Chitons live from shallow water to the deep sea, but the majority of species live in the intertidal. This is a high-energy habit characterized by the bashing of waves as the tide rises and falls twice daily. Any organism living here must be able to hang on for dear life or risk being swept away to certain death. Chitons are certainly well equipped to survive in this habitat. They have a low profile, offering minimal resistance to the waves. Rather than stand tall and face the brunt of the wave energy, chitons cling tightly to the rocks and let the waves wash over them.

Tonicella lokii at Monastery Beach
27 October 2015
© Allison J. Gong

The chiton’s shell, divided into eight articulating plates, gives the animal a much more flexible shell than is found in any other mollusc. This allows them to conform to the topography of the rocks, giving them an even lower profile than, say, a limpet of the same overall shape and size.

While most chitons are pretty sedentary, at least during the low tides when we can see them, some of them can move pretty quickly when they want. So what, exactly, motivates a chiton to run? One species, Stenoplax heathiana, lives on the underside of rocks in the intertidal; it comes out at night to forage on algal films and retreats back under its rock with the dawn. I’ve seen them at Pistachio Beach, where I turned over rocks and watched them run away from the light. This video is shot in real-time; the chitons are really running fast!

When the eight shell plates are visible it’s easy to identify a chiton as a chiton. But not all chitons are quite so obliging with their most chiton-ish characteristic, and one is downright misleading.

Below is Katharina tunicata, one of the largest chitons on our coast. Its shell plates are barely visible, as they are almost entirely covered by the animal’s mantle, the layer of tissue that covers the visceral mass and encloses an open space called the mantle cavity in which the gills are located. In chitons, the mantle extends onto the dorsal side of the animal and is called the girdle. Katharina‘s girdle is smooth and feels like wet leather.

The chiton Katharina tunicata at the Great Tidepool in Pacific Grove
26 October 2015
© Allison J. Gong

The largest chiton in the world is the gumboot chiton, Cryptochiton stelleri, and it lives on our coast. This beast is about the size of a football, reaching a length of 30 cm or so. It lives mostly in subtidal kelp forests, but can be found in the very low intertidal, which is where I usually see it. At first encounter it’s hard to figure out what this animal is. It certainly doesn’t look like a chiton.

A large Cryptochiton stelleri at Mitchell’s Cove
6 June 2016
© Allison J. Gong

If anything, it looks like a mostly deflated football, doesn’t it? Turning it over to look at the underside doesn’t help much, either, although this photo does give an idea of how big the animal can get:

Ventral view of Cryptochiton stelleri at Pigeon Point
24 April 2016
© Allison J. Gong

Cryptochiton goes one beyond Katharina and covers its plates entirely. Just looking at the animal you’d have no idea that there are eight plates underneath the tough reddish-brown mantle, but you can feel them if you run your finger along the midline of the dorsum. Living subtidally as it does, Cryptochiton doesn’t have the ability to cling tightly to rocks that its intertidal relatives do, and it tends to get washed off its substrate and cast onto the beach during storms. I’ve never seen one on the beach that wasn’t very dead. Once a friend and I were trudging back up the beach after working a low tide, and encountered a dead softball-sized Cryptochiton. I mentioned that it would be nice to have a complete set of shell plates from one of these animals. My friend always carries a knife in her pocket, so we started an impromptu dissection right there on the beach. It didn’t take long to learn that the mantle of a gumboot chiton is really tough and difficult to cut through with a pocket knife. And even once we got through the mantle, dissecting the plates from the underlying tissue wasn’t going to happen with the tools we had with us. Besides, the stench was godawful even with our unusual tolerance for the smell of dead sea things. We abandoned that corpse.

Single plate of the gumboot chiton, Cryptochiton stelleri
16 May 2017
© Allison J. Gong

Many beachcombers have found white butterfly-shaped objects in the sand, but not known what they are. They are definitely calcareous and feel like bone, but what kind of animal makes a bone shaped like this? Turns out this object is one of the shell plates from C. stelleri. They wash up frequently, never attached to their neighbors so they provide no clue as to what organism they came from.

In order to obtain a complete set of Cryptochiton plates, I’d have to start with an intact chiton corpse. I did happen upon another dead Cryptochiton on a beach somewhere I was allowed to collect organisms, and I brought it back to the marine lab. I remember spending a smelly afternoon cutting the plates out of the corpse and removing as much of the tissue as I could, then feeding the plates to various hungry anemones to take care of the rest. Some of the plates got a little broken during the extraction process, but I do have my very own full set!

Shell plates of Cryptochiton stelleri
16 May 2017
© Allison J. Gong

Some day I will figure out a way to mount those plates permanently.

One final question to ponder. Does a chiton have one shell, or eight shells?

Friends in strange places

Posted on by Allison J. Gong

Animal associations can be strange and fascinating things. We’re used to thinking about inter-specific relationships that are either demonstrably good or bad. Bees and flowering plants–good. Mosquitos on their vertebrate hosts–bad. In many cases the ‘goodness’ or ‘badness’ of these associations is pretty clear. However, there are cases of intimate relationships between animals of different species that cannot be easily categorized as good or bad.

Take, for example, the barnacles on the skin of gray and humpback whales. From the barnacles’ perspective the skin of a whale isn’t a bad place to live: as the whale swims through the water the barnacle is continually flushed by clean water, which should make feeding easier. But is the whale affected in any way by its barnacle passengers? I suppose they might increase the drag coefficient a little bit and make swimming marginally less efficient, and maybe they itch, although it’s hard to imagine that the whale would really care much one way or the other.

A week ago I went to the intertidal up at Pigeon Point. It’s a great spot for certain animals, especially the small six-rayed stars of the genus Leptasterias. These stars rarely get larger than 8 cm in diameter and always have six arms. I’ve been told by a friend who just happens to be a sea star taxonomist at the Smithsonian, that making species identifications in the field is very difficult for this genus, so I’ve stopped trying. I do know that some of the Leptasterias stars have slender rays and others have thicker rays.

Two stars of the genus Leptasterias, at Pigeon Point
9 May 2016
© Allison J. Gong

The most common large star at Pigeon Point is the bat star, Patiria miniata. These stars get about as big as my outstretched hand, and come in a variety of colors. Last week I didn’t see very many Patiria, but all of them were reddish orange, like this one:

Bat star (Patiria miniata) at Pigeon Point
30 April 2017
© Allison J. Gong

Unless they’re so abundant as to be annoying, I like picking up bat stars and looking at their underside. That’s because sometimes they have these little dark squiggles in their ambulacral groove:

Patiria miniata with commensal worm, at Pigeon Point
30 April 2017
© Allison J. Gong

That little squiggle is a polychaete worm, Oxydromus pugettensis. It is one of many polychaete worms that forms a symbiotic relationship with another animal species. Some symbiotic polychaetes live in the tubes of other worms, or within the shells of bivalves, for example. Oxydromus crawls around inside the ambulacral groove of Patiria, where it feeds on scraps of leftover food from the star’s meals. The worms don’t like light, and as soon as I picked up this star and flipped it over the worm started burrowing down between the star’s tube feet to get back to the dark. The next day I found another star with a worm and was able to take a picture of it before it disappeared.

Commensal worm (Oxydromus pugettensis) in the ambulacral groove of Patiria miniata, at Pigeon Point
1 May 2017
© Allison J. Gong

Oxydromus pugettensis is clearly segmented, evidence of its annelidan roots. It doesn’t look very different from many other free-crawling polychaetes. A member of the family Hesionidae, it lives in fine silty sediments in the intertidal as well as in the ambulacral grooves of sea stars. According to one source, it is the most common intertidal member of its family along the California and Oregon coast. For reasons as yet undetermined, P. miniata seems to be the favored host, although I have also seen the worms in the ambulacral grooves of the leather star Dermasterias imbricata.

Over two days at Pigeon Point last week I examined a total of five bat stars, and all of them had worms. One of the stars had three worms! It’s possible that more worms were hiding deep within the ambulacral grooves, too. I always wonder how, in this type of association, the partners manage to find each other. How does one “lucky” star end up with three worms? Do the worms every migrate from one star to another? Does the star do anything to attract the worms? In what way(s) would the star benefit from having a few worms in its ambulacral regions? It does seem that the worms don’t stick around very long once a star is brought into the lab–I don’t know if they die or just leave on their own–but since they also live in the sand maybe they do actively migrate between stars. There hasn’t been much work done on these worms in recent decades, probably because of the overall decline in natural history studies. However, I’ll keep this worm in mind for my Marine Invertebrate Zoology students this fall, when one of them asks me for help coming up with an idea for his or her independent research project.

Gastropods x3

Posted on by Allison J. Gong

This past Monday I did something rare for me: I returned to the same intertidal site I had visited the previous day. I enjoyed myself so much the first time that I wasn’t able to refuse an invitation to go out there again. The site, Pigeon Point, is one of my favorites, especially in all of its spring glory as it is now. It has always been a hotspot especially for macroalgal diversity, and so far this year appears to be living up to its reputation. The day before I collected several reds that I got to spend the next two days trying to identify.

Three intertidal gastropods at Pigeon Point. Top circular object: Thylacodes squamigerus; yellow elongated object in middle: Doriopsilla albopunctata; bottom purplish-black snail: Tegula funebralis.
1 May 2017
© Allison J. Gong

On Monday I was less overwhelmed by obsessed with algae and able to focus more on the animals, and was delighted to find a small cluster of Thylacodes squamigerus, the strange and fascinating vermetid snail. Nearby one of the vermetid snails was a yellow nudibranch (Doriopsilla albopunctata) and one of the common turban snails (Tegula funebralis). The chance proximity of three different gastropods brought to mind the incredible diversity of this group of molluscs.

The Gastropoda are the largest group within the phylum Mollusca, and can claim a fossil record that dates back to the early Cambrian, some 540 million years ago. They have been extremely successful throughout that long time and are the only molluscan group to have established lineages in both freshwater and on land (of the other molluscs, only the bivalves have made it into freshwater, with the remaining groups restricted to the sea). As you might expect, this evolutionary history has given rise to a mind-boggling array of body types and lifestyles. Let’s investigate this diversity by taking a closer look at the three gastropods in the photo above.

Gastropod #1 (Thylacodes squamigerus): Very few people, on seeing this animal for the first time, would guess that it’s a snail. Most would say that it’s a serpulid worm. The tube is calcareous, as it is for serpulid worms, and winds around over rocks in the intertidal.

Tube of the vermetid snail Thylacodes squamigerus at Pigeon Point
1 May 2017
© Allison J. Gong

A close look at the opening of the tube, however, reveals snail-like rather than worm-like features. Thylacodes even has a snail’s face, although I’ll admit it isn’t easy to see if you don’t know to look for it. And despite crawling under a ledge with my camera, I didn’t get the best view of a face. In this photo, however, you can at least see one of the cephalic tentacles:

View into the tube of Thylacodes squamigerus at Pigeon Point
1 May 2017
© Allison J. Gong

Living in a tube cemented onto a rock means that Thylacodes can’t go out and find food. It must instead catch food and bring it in. Thylacodes does so by spinning threads of sticky mucus that are splayed out into the water, where they capture plankton and suspended detritus. The threads are then reeled in and everything–mucus and food–is eaten by the snail. Thylacodes tends to occur in groups, and individuals within an aggregation contribute threads to a communal feeding net, which presumably can catch more food than the sum total of all the snails’ individual efforts.

Pretty unexpected for a snail, isn’t it?

Gastropod #2 (Tegula funebralis): The black turban snail is probably one of the most common and commonly overlooked animals in the intertidal. People don’t see them because these snails are, literally, everywhere from the high- down into the mid-intertidal. They are routinely stepped over as visitors rush to the lower intertidal, and ignored again as these same visitors leave the seashore. I love them. I keep them in the lab as portable lawnmowers for the seawater tables. They are incredibly efficient grazers, keeping the algal growth down. Plus, I think they’re cute!

If there’s such thing as a ‘typical’ marine snail, T. funebralis may very well be it. This little snail exemplifies several of the traits we use to define the Gastropoda: it lives in a coiled shell, it uses a radula for scraping algal film off rocks (yum!) and is torted. The shell is easy enough to understand, as everyone has seen a snail at some point, even if it was a terrestrial snail. The radula and torsion, however, may take a little explaining.

A congregation of Tegula funebralis at Mitchell’s Cove
8 June 2016
© Allison J. Gong

Many molluscs have a radula, a file-like ribbon of teeth that can be stuck out of the mouth and used for feeding. In gastropods the radula can be a scraping organ (as in Tegula and other herbivores such as limpets), a drill (as in the predatory moon snails, which drill holes into unsuspecting clams and then slurp out their soft gooey bodies), or a poison dart (as in the venomous cone snails). The radula of a grazer such as Tegula bears many transverse rows of sharp teeth, which are regularly replaced in a conveyor belt fashion as they are worn down. This assures that the teeth being used are always nice and sharp. Remember the radula marks made by the owl limpet (Lottia gigantea)?

An owl limpet (L. gigantea) in her farm at Natural Bridges
7 March 2017
© Allison J. Gong
Tegula funebralis clearing real estate in my seawater table
27 January 2017
© Allison J. Gong

Those zig-zaggy marks are made by the scraping of the radula as the limpet crawls over her farm. Tegula funebralis makes the same type of pattern in my seawater tables. All of that white territory is area that had been scraped clean of algae in about a day. Tegula is a very industrious little snail! And they’re not shy, either. I don’t have to wait a day or so for them to get acclimated when I bring the back to the lab. I can move them around from table to table and after a few seconds they poke their heads out and start cruising around. I’ve learned from watching them over the years that they seem to have an entrained response to the rising and falling of the tides, even after I bring them into the lab. For the first few weeks of captivity, every morning when I first get to the lab I find that several Tegula have climbed up the walls. I think they’re crawling up when the tide is high. I really should look at that more carefully. They never go too far, but sometimes they do drop onto the floor and I find them by stepping on them. Fortunately they are hardy creatures and the floor is always wet with seawater so as long as I find them within a day and plunk them back into the table they’re fine.

Now on to torsion. Torsion is difficult to explain, but let me try. The word ‘torsion’ refers to the twisting of the nerve cord and some internal organs that occurs during larval development of gastropods. Here’s how it works. Imagine a closed loop, like a long piece of string with the ends tied together. Lay the loop down on a table and it is just a simple loop. Pick up one end of the loop, twist it counterclockwise 180°, and lay it down again. Now you have a figure-8, right? That’s not exactly what happens in the living snail, but you get the picture.

Tegula and other snails have an elongated body that is coiled and crammed to fit inside the shell. If you could take Tegula’s body and stretch it out without breaking it (impossible to do, BTW), you’d see the figure-8 configuration of the nerve cord. Other internal organs are re-arranged by torsion, too. As a result, both the gill(s) and the anus now open into the mantle cavity which has been relocated over the head. This arrangement is ideal for keeping the gill(s) irrigated, but not so good for hygienic reasons. Fortunately, the mantle cavity itself is angled so that water flows through it in a more-or-less unidirectional manner, passing over the gill before the anus. Tegula and other marine snails undergo torsion while in the larval stage, and remain torted as adults. This is not the case in other gastropods, as we’ll see next.

Gastropod #3 (Doriopsilla albopunctata): Everybody loves the nudibranchs, because their brilliant colors make them easy to love. Unlike the oft-undetected Thylacodes squamigerus and the ignored Tegula funebralis, many of the nudibranchs are somewhat easy to spot in the field because of their flamboyance. This is a crappy picture, but you get the point.

Doriopsilla albopunctata at Point Piños
9 May 2015
© Allison J. Gong

Doriopsilla albopunctata is one of several species of yellow dorid nudibranchs lumped together under the common name ‘sea lemon’. Instead of the long fingerlike processes (cerata) that adorn the backs of the aeolid nudibranchs such as Hermissenda spp., the dorids have smooth or papillated backs that may be decorated with rings or spots. Dorids also have a set of branchial plumes on the posterior end of the dorsum; the number and color of these gills can often be used to distinguish similar species. Doriopsilla albopunctata has a smooth yellow back with little white spots, hence the species epithet (L: ‘albopunctata’ = ‘white pointed’), and white branchial plumes.

Doriopsilla albopunctata at Franklin Point
17 July 2015
© Allison J. Gong

Nudibranchs are gastropods, although in a different group from Thylacodes and Tegula. The marine slugs, of which the nudibranchs are the most commonly encountered, are in a group called the Opisthobranchia, whose name means ‘gill on back’ and refers equally to the cerata of aeolids and the branchial plume of dorids. In fact, these animals lack the typical molluscan gill that the snails have. They do have a radula, however, and crawl around on a single foot exactly like Tegula does.

An adult nudibranch’s body is elongated, unlike the coiled body of Tegula, and has no apparent signs of having undergone torsion. However, examination of larval nudibranchs shows that they do undergo torsion just like any other respectable gastropod. The weird thing is that some time during the transition from pelagic larva to benthic juvenile they de-tort, or untwist their innards so that their internal anatomy matches their external shape. Instead of having to poop on their own heads, nudibranchs have an anus that is sensibly located at the rear (no pun intended) of the body.

Torsion is one of those biological curiosities whose evolutionary origin is shrouded in mystery. How did such anatomical contortions evolve? Why do gastropods, and only gastropods, undergo torsion? And why do some gastropods tort as larvae, only to detort as they become adults? There are scientific hypotheses about the benefits of torsion, particularly to the larval stages, but nobody knows for sure. After all, none of use were there to watch when it happened.

This is just a tiny taste of the diversity of the Gastropoda. I think it’s cool to see three such different gastropods in a small spot of the intertidal. And no doubt there were more that I didn’t see. That’s one of the joys of working in the intertidal: that I so often see things I wasn’t even trying to find.

Different strokes

Posted on by Allison J. Gong

When it comes to the natural world, I have always found myself drawn to things that are unfamiliar and strange. I think that’s why I gravitated towards the marine invertebrates: they are the animals most unlike us in just about every way imaginable. Even so, some of them have bodies at least that are recognizable as being both: (1) alive; and (2) animal-ish. Think, for example, of a lobster and a snail. Each has a head and the familiar bilateral symmetry that we have. Obviously they are animals, right? I, of course, am most fascinated not by these easy-to-understand (not really, but you know what I mean) animals, but to the cnidarians and the echinoderms. And for different reasons. The cnidarians astound me because they combine morphological simplicity with life cycle complexities that boggle the mind. I hope to write about that some day. Today’s post is about my other favorite phylum, the Echinodermata.

For years now I’ve been spawning sea urchins, to study their larval development and demonstrate to students how this type of work is done. I have a pretty good idea of what to expect in urchin larvae and can claim a decent track record of raising them through metamorphosis successfully. Urchins are easy. To contrast, I have much less experience working with sea stars. I have found that some species are easy to work with, while others are much more problematic. Bat stars (Patiria miniata), for instance, are easy to spawn and raise through larval development into post-larval life. Ochre stars (Pisaster ochraceus), on the other hand, go through larval development beautifully, but then all die as juveniles because nobody has figured out what to feed them. I’ve already chronicled my and Scott’s attempts in 2015 to raise juvenile ochre stars in a series of posts starting here.

Sea urchins and sea stars have long been model organisms for the study of embryonic development in animals, for a few reasons. First, many species of both kinds of animals are broadcast spawners, which in nature would simply throw their gametes out into the water. This means that development occurs outside the mother’s body, so biologists can raise the larvae in the lab and observe what happens. Second, spawning can be induced by subjecting the parents to nonlethal chemical or environment stresses. Third, the larvae themselves are often quite happy to grow in jars and eat what we feed them. Fourth, the larvae of the planktotrophic species are often beautifully transparent, allowing the observer to see details of internal anatomy. Lucky me, I’ve been able to do this several times. And it never gets old.

All that said, there are differences between urchins and stars that force the biologist to treat them differently if we want them to spawn. For the species I work with, spawning occurs after I inject a certain magic juice into the animals’ central body cavity–urchins get a simple salt solution (KCl, or potassium chloride) and stars get a more complex molecule (1-MA, or 1-methyladenine). The fact that you can’t use the same magic juice for urchins and stars reflects a fundamental difference in gametogenesis and spawning in these groups of animals.

Female (left) and male (right) spawning purple sea urchins (Strongylocentrotus purpuratus)
20 January 2015
© Allison J. Gong

Sea urchins will spawn only if they have fully developed gametes. In other words, gametogenesis must be complete before gametes can be released to the outside. You can inject as much KCl into a sea urchin as you want, but if it’s the wrong time of year or the urchin doesn’t have mature gonads (due to poor food conditions, perhaps), it won’t spawn. I’ve never investigated the mechanism by which KCl induces spawning in ripe urchins, but here’s what I think happens.

When students dissect animals in my invertebrate zoology class, we use magnesium chloride (MgCl2) to narcotize the animals first. A 7.5% solution of this simple salt is remarkably effective at putting many animals gently to sleep, especially molluscs and echinoderms. Placing the animals in a bowl of MgCl2 and seawater causes them to relax and gradually become unresponsive. A longer bath in the MgCl2 puts them to sleep for good.

Given the relaxation effects of MgCl2 on urchins, I suspect that injecting a solution of KCl into the body cavity relaxes the sphincter muscles surrounding the gonopores. This relaxation opens the gonopore, and if the gonads are ripe the mature gametes are released to the outside. As I said above, I don’t know for certain if this is how it works, but the hypothesis makes sense to me. It also explains why that I can shoot up a dozen urchins and get none of them to spawn: the KCl might be doing what it normally does (i.e., opening the gonopores) but if the gonads aren’t ripe there are no gametes to be released.

For completely different reasons, injecting a star with KCl does absolutely nothing at all except probably make the animal a bit uncomfortable. The KCl may very well open gonopores as it does in urchins, but a star will never have mature gametes, especially eggs, to release in response to this muscle relaxant. This is because at least in female stars, meiosis (the process that produces haploid gametes) isn’t complete until the eggs have been spawned to the outside. What, then, is the magic juice used to induce spawning in stars, and what exactly does it do?

The magic juice is 1-methyladenine, a molecule related to the nucleobase adenine, most commonly known as one of the four bases that make up DNA. The nomenclature indicates that the difference between the two molecules is the addition of a methyl group (–CH3) to the #1 position on an adenine molecule:

Chemistry aside, what I’m interested in is the action of 1-MA on the eggs of sea stars. Meiosis, the process that produces gametes, has two divisions called Meiosis I and II. Meiosis I starts with a diploid cell (i.e., containing two sets of chromosomes) and produces two diploid daughter cells; these daughter cells may not be genetically identical to each other because of recombination events such as crossing over. It isn’t until Meiosis II, the so-called reduction division, that the ploidy number is halved, so each daughter cell is now haploid (i.e., containing a single set of chromosomes) and can take part in a fertilization event. In a nutshell, the end products of meiosis are haploid cells, all of which ultimately result from a single diploid parent cell.

In female sea urchins, the entire meiotic process is completed before the eggs are spawned, which is why the relaxation effects KCl can induce spawning.

In females of many other animal species, meiosis is arrested for some period of time after the Meiosis I division. For example, this happens in humans: baby girls are born with all of the eggs they will ever produce, maintained in a state of suspended animation after Meiosis I. It isn’t until puberty that eggs begin to complete meiosis, one egg becoming mature and being ovulated approximately monthly for the rest of the woman’s reproductive life. Sea stars are sort of like this, with the notable exception that a female star will ripen and produce thousands of eggs in any spawning event rather than doling them out one at a time.

One of the really cool things about working with sea star embryology is that I get to see the completion of meiosis after the eggs have been spawned. I know that the gonads have to reach a certain level of ripeness before 1-MA will induce spawning. Reviewing my notes from a course I took in comparative invertebrate embryology when I was in graduate school, I came across the mention of ‘polar bodies,’ tiny blobs that I remember seeing in just-fertilized sea star eggs but which I have never seen in sea urchin embryos. Then I needed to remind myself what polar bodies are all about.

Remember how there are two cell divisions in meiosis? Well, despite what’s shown in the diagram above, each of the divisions is asymmetrical. In other words, each division of meiosis produces one big cell and one tiny cell. The tiny cells are the polar bodies. They are too small to either divide or be fertilized, and generally die on their own. Here’s a chronology of what happens. First, a cell divides, producing a large cell and a tiny polar body:

I’ve x’d out the polar body in red because it cannot divide or be fertilized and will soon die. Then the large cell divides to produce the final egg and a second polar body:

It turns out that in sea stars things get even more complicated. 1-MA acts as a maturation-inducing substance in these animals, effectively jump-starting the eggs that have been sitting around in an arrested state after undergoing Meiosis I. This initiates the continued maturation of the eggs to the stage when they can be spawned. Even now, though, meiosis doesn’t complete until an egg has been fertilized, at which point the second polar body is produced. The production of that second polar body is the signal that Meiosis II has occurred, and the now-fertilized egg can begin its embryonic development.

Here’s a freshly fertilized egg of Pisaster ochraceus, with the two polar bodies smushed into the narrow perivitelline space between the surface of the zygote and the fertilization envelope:

Zygotes of the ochre star Pisaster ochraceus, showing two polar bodies
25 April 2017
© Allison J. Gong

Sea urchins, remember, do not have polar bodies when I spawn them. That’s because meiosis is complete by the time the eggs can be spawned, so the polar bodies have already died or been resorbed by the final mature egg. The photo of the P. ochraceus zygotes was taken within a few minutes of fertilization. Let’s contrast that with a photo of a brand new urchin zygote:

Egg of purple sea urchin (Strongylocentrotus purpuratus) fertilized by sperm from a red urchin (Mesocentrotus franciscanus)
30 December 2016
© Allison J. Gong

See? No polar bodies!

All of this is to explain why we can’t use the same magic juice to spawn both urchins and stars. Kinda cool when the madness in our method has a biological context, isn’t it?

Ghosts

Posted on by Allison J. Gong

I seem to have a need to keep investigating seastar wasting syndrome (SSWS) and trying to make sense of what I and others see in the field. I think it parallels my morbid fascination with the medieval Black Death. In any case, I’ve devised a plan to continue experimenting with one aspect of the potential recovery of one species, the ochre star, Pisaster ochraceus.

The first step of this plan was to collect a few more stars, which I did back in early March. For the past year or so the stars had been becoming more abundant at certain sites, leading to hope that the populations were beginning to recover and speculation as to whether these individuals were pre-SSWS survivors or post-SSWS recruits. I think they are survivors, because it seems highly unlikely that a star can grow from teensy (a few millimeters in diameter) to hand-sized on a few years. This is what I want to address experimentally in the lab.

The three stars that I collected seemed to adjust well to life in the lab. They all ate well and were crawling around in their tank. Then, last Friday (31 March 2017, to be exact) I checked on the stars as I usually do and was horrified to see this:

Dismembered bits of an ochre star (Pisaster ochraceus)
31 March 2017
© Allison J. Gong

Knowing from experience how quickly this can happen, I’d guess this star had begun ripping itself into pieces in the previous 24 hours. And meantime, its tankmates had stuck themselves to the underside of the cover of the tank. This is not unusual behavior and once I poked them both to make sure they weren’t getting mush I decided not to worry about them for the time being. The important thing was to remove the not-dead-yet pieces of the exploded star and bleach the tank before returning the apparently healthy stars to it.

One of the most horrific aspects of SSWS is that it is both blindingly fast and agonizingly slow. It appears to strike out of the blue, by which I mean that stars can look absolutely fine one afternoon and be torn to bits the next morning. And it’s slow because the individual pieces can live for hours or even days before finally dying.

31 March 2017
© Allison J. Gong

This star broke itself into five pieces. The three pieces of arm had started getting mushy but still responded by sticking harder when I picked them up. That larger section with two arms and the madreporite was actually walking around the bowl. The torn-off pieces were all oozing sperm into the water, so at least I know this individual was a male. Small comfort, that, when I had to bag up the pieces and throw them in the trash.

Being confronted with the specter of SSWS, I wondered exactly what it meant. I’ve never been under the illusion that SSWS goes away entirely. I suspect that it is always present in the wild, possibly at low enough levels that we don’t notice it for decades at a time. Seeing one dead star, which presumably was infected in the field before I brought it into the lab. . . does it mean the plague is rearing its ugly head again? Or is this a one-off that I just happened to catch? There’s only one way to find out, and that is to see if there are more sick stars in the field. So that’s what I did the following two days. I had planned to visit three intertidal sites where I expect Pisaster ochraceus to live, but my concussed brain allowed me to drive to only the two nearest sites.

I went to Natural Bridges on Saturday, where I’d been seeing lots of ochre stars over the past several months. I hadn’t seen a sick star there for years, although at the outbreak of the plague in 2013 the ochre stars disappeared suddenly. In the past couple of years I’d been happy to see lots of healthy hand-sized stars there. Last weekend it seemed I saw fewer stars than I had gotten used to seeing, but none of them were sick. Whew!

Pair of healthy Pisaster ochraceus at Natural Bridges
1 April 2017
© Allison J. Gong

The next day I went to Mitchell’s Cove, where I’d collected those three stars back in March. I did see lots of great-looking stars, some as small as ~6 cm in diameter and others bigger than my outstretched hand.

Trio of healthy Pisaster ochraceus at Mitchell’s Cove
2 April 2017
© Allison J. Gong

But I also saw this:

Arm of a P. ochraceus that was killed by SSWS at Mitchell’s Cove
2 April 2017
© Allison J. Gong

This is all that remains of an ochre star that apparently succumbed to SSWS. No other body parts are visible in the vicinity, and this arm bit was barely hanging on to the rock. Given how quickly stars can disintegrate when SSWS hits, this one probably began showing symptoms the previous day, while the tide was in and nobody would have seen it. And who knows how many other stars got sick and died without anybody noticing.

The take-home message is that I need to not let SSWS fall off my mental radar. I hope to god that my six remaining P. ochraceus in the lab remain healthy and that I can spawn them in a couple of weeks. I’ve obtained from a friend some small dishes seeded with food that tiny juvenile stars may be able to eat. I’m not too worried about getting through the larval development stage, although I probably shouldn’t get too cocky about that. In any case, it’s the post-larval juvenile survivorship that I’m really interested in. This year I don’t have Scott to help me with the husbandry and data collection. I will instead be working with another colleague, Betsy. We have a spawning date at the end of April, when the next phase of my ongoing SSWS investigation will begin.

Complexity in small packages

Posted on by Allison J. Gong

Last week I went up to Davenport to do some collecting in the intertidal. The tide was low enough to allow access to a particular area with two pools where I have had luck in the past finding hydroids and other cool stuff. These pools are great because they are shallow and surrounded by flat-ish rocks, so I can lie down on my stomach and really get close to where the action is. At this time of year the algae and surfgrasses are starting to regrow; the surface of the pools was covered by leaves of Phyllospadix torreyi, the narrow-leafed surfgrass.

Parting the curtain of Phyllospadix leaves to gaze into the first pool I was pleasantly surprised to find this. What does it look like to you?

Aglaophenia latirostris at Davenport Landing
8 March 2017
© Allison J. Gong

There are actually two very different organisms acting as main subjects in this photo. The pink stuff is a coralline alga, a type of red alga that secretes CaCO3 in its cell walls. Coralline algae come in two different forms: one is a crust that grows over surfaces and the other, like this, grows upright and branching. Because they sequester CaCO3, corallines are likely to be affected by the projected increase of the ocean’s acidity due to the continued burning of fossil fuels. Ocean acidification is one of the sexy issues in science these days, and although it is very interesting and pertinent to today’s world it is not the topic for this post. Suffice it to say that changes in ocean chemistry are making it more difficult for any organisms to precipitate CaCO3 out of seawater to build things like shells or calcified cell walls.

It’s the tannish featherlike stuff in the photo that I was particularly interested in. At first glance the tan thing looks like a clump of a very fine, fernlike plant. It is, however, an animal. To be more specific, it is a type of colonial cnidarian called a hydroid. I love hydroids for their hidden beauty, not always visible to the naked eye, and the fact that at first glance they so closely resemble plants. In fact, many hydroid colonies grow in ways very similar to those of plants, which has often made me think that in some cases the differences between plants and animals aren’t as great as you might assume. But that’s a matter for a separate essay.

I collected this piece of hydroid and brought it back to the lab. The next day I took some photos. To give you an idea of how big the colony is, the finger bowl is about 12 cm in diameter and the longest of these fronds is about 3 cm long.

Colony of the hydroid Aglaophenia latirostris
9 March 2017
© Allison J. Gong

And here’s a closer view through the dissecting scope.

The colonial hydroid Aglaophenia latirorostris
9 March 2017
© Allison J. Gong

Each of the fronds has a structure that we describe as pinnate, or featherlike–consisting of a central rachis with smaller branches on each side. This level of complexity can be seen with the naked eye. Zooming in under the scope brings into view more of the intricacy of this body plan:

Close-up view of a single frond of Aglaophenia latirostris, showing feeding polyps and two gonangia
9 March 2017
© Allison J. Gong

At this level of magnification you can see the anatomical details that cause us to describe this animal’s structure as modular. In this context the term ‘modular’ refers to a body that is constructed of potentially independent units. A colony like this is built of several different types of modules called zooids, some of which are familiarly referred to as polyps. Each zooid has a specific job and is specialized for that job; for example, gastrozooids are the feeders, while gonozooids take care of the sexual reproduction of the colony. In this colony of Aglaophenia each of these side branches consists of several stacked gastrozooids, which you can see as the very small polyps bearing typical cnidarian feeding tentacles. Aglaophenia is a thecate hydroid; this means that each gastrozooid sits inside a tiny cup, called a theca, into which it can withdraw for protection. Those larger structures with pinkish blobs inside are called gonangia. A gonangium is a modified gonozooid, found in only thecate hydroid colonies, that contains either medusa buds or other reproductive structures called gonophores.

Pretty complicated, isn’t it? Who would expect such a small animal to have this much anatomical complexity?

In the second pool I found an entirely different type of hydroid. At first glance this one looks more animal-like than Aglaophenia does, although it is still a strange kind of animal. This is Sarsia, one of the athecate hydroids whose gastrozooids do not have a protective theca. It might be easier to think of these and other athecate hydroids (such as Ectopleura, which I wrote about here and here) as naked, with the polyps not having anywhere to hide.

Colony of the athecate hydroid Sarsia sp.
9 March 2017
© Allison J. Gong

Each of these polyps is about 1 cm tall. The mouth is located on the very end of the stalk. The tentacles, not quite conforming to the general rule of cnidarian polyp morphology, do not form a ring around the mouth. Instead, they are scattered over the end of the stalk.

Here’s a closer view:

Colony of the athecate hydroid Sarsia sp.
9 March 2017
© Allison J. Gong

In the hydroid version of Sarsia, the reproductive gonozooids are reduced to small buds that contain medusae. You can see a few round pink blobs in the lower right of the colony above; those are the medusa buds.  The medusae are fairly common in the local plankton, indicating that the hydroid stage is likewise abundant. Here’s a picture of a Sarsia medusa that I found in a plankton tow in May 2015.

Medusa of the genus Sarsia
1 May 2015
© Allison J. Gong

The medusa of Sarsia is about 1 mm in diameter and has four tentacles, which usually get retracted when the animal is dragged into a plankton net. Sometimes, if the medusa isn’t too beat up, it will relax and start swimming. I recorded some swimming behavior in a little medusa that I put into a small drop of water on a depression slide. It refused to let its tentacles down but you might be able to distinguish four tentacle bulbs.

There’s a lot more that I could say about hydroids and other cnidarians. They really are among the most intriguing animals I’ve had the pleasure to observe, both in the field and in the lab. I’ve always been fascinated by their biphasic life cycle, with its implications for the animals’ evolutionary past and ecological present. Perhaps I’ll write about that some time, too.

Metamorphosis

Posted on by Allison J. Gong

It has been a few weeks since I posted about my most recent batches of urchin larvae. Some strange things have been happening, and I’m not yet sure what to make of them. It would be great if animals cooperated and did what I expect; somehow that never seems to be the case. The upshot of all this uncertainty is that there is always something new to learn. I, for one, am not going to complain about that.

One noteworthy thing to report is that my hybrids all died, very quickly and unexpectedly. They had been racing through development and on the dreaded Day 24 they looked great.

Hybrid larvae of purple urchin (Strongylocentrotus purpuratus) eggs fertilized by red urchin (Mesocentrotus franciscanus) sperm, age 24 days.
23 January 2017
© Allison J. Gong

And the next time I changed their water, they were all dead. So much for the hybrid vigor I had written about earlier. Teach me to get cocky and think I know what’s going on.

Fast forward to Day 52, and some of the cultures are still going strong. I originally set up four matings, and at least some individuals from each are alive. One thing that seems to happen when I start multiple batches of larvae at the same time is that the batch with the fewest numbers does the best. This time my F3xM1 mating was always the least dense culture, but some of them have already begun and completed metamorphosis. And the ones that are metamorphosing are the ones being fed what I expected to be the less desirable food source. As I said, not much of this whole experience is making sense.

The good thing is that I have an opportunity to observe these larveniles in action. As long as they don’t get arrested in this neither-here-nor-there stage, they should soon join their siblings as permanent inhabitants of the benthos.

This video contains short clips of three different larveniles. I’ve arranged the clips from earlier to later stages of metamorphosis. Although these are three separate individuals, you can imagine that each one goes all of these stages.

Having both tube feet (for crawling around the benthos) and ciliated bands (for swimming in the plankton) make these animals unsuited for either habitat. They have gotten very heavy and sink to the bottom, but it doesn’t take much water movement to knock them off their five little tube feet. It always amazes me that teensy critters like this, so fragile and easily killed, manage somehow to stick in the intertidal and survive long enough to be grown-up urchins on their own. And yet some of them will. I’ve seen it happen.

Beginnings and leavings

Posted on by Allison J. Gong

A few days ago I was in the intertidal with my friend Brenna. This most recent low tide series followed on the heels of some magnificently large swells and it was iffy whether or not we’d be able to get out to where we wanted to do some collecting. Our first day we went up to Pistachio Beach, just north of Pigeon Point, where the rocky intertidal is bouldery and protected by some large rock outcrops.

Pigeon Point lighthouse, viewed from Pistachio Beach.
27 January 2017
© Allison J. Gong
27 January 2017
© Allison J. Gong

So while the swell was indeed really big, we were pretty well protected in the intertidal. The Seymour Center has a standing order for slugs, hermit crabs, and algae. I was easily able to grab my limit (35) of hermit crabs over the course of the afternoon, and while it’s too early in the season for the algae to do much I had my sluggy friend with me to take care of finding nudibranchs, which left me free to let my attention wander as it would.

Codium setchellii at Pistachio Beach.
27 January 2017
© Allison J. Gong

The very first thing to catch my eye as we go out there was the coenocytic green alga Codium setchellii, which I wrote about last time. I’ve seen and collected C. setchellii from this site before, but don’t remember seeing it in such large conspicuous patches. I need to review what I learned about the phenology of various intertidal algae, but here’s a thought. Maybe Codium is an early-season species that gets outcompeted by the plethora of fast-growing red algae later in the spring. Red algae were present at Pistachio Beach but not in the lush (and slippery!) abundance that I’ll see in, say, June. I’m willing to bet that Codium will be less abundant in the next few months.

Leptasterias sp. at Pigeon Point.
24 April 2016
© Allison J. Gong

In my experience, the six-armed stars of the genus Leptasterias have always been the most abundant sea stars on the stretch of coastline between Franklin Point and Pescadero. Even though they are small–a monstrously ginormous one would be as large as the palm of my hand–they are very numerous in the low-mid intertidal. I’ve seen them in all sorts of pinks and grays with varying amounts of mottling. Alas, I don’t know of any really reliable marks for identifying them to species in the field.

Unlike other familiar stars, such as the various Pisaster species and the common Patiria miniata (bat stars), which reproduce by broadcast spawning their gametes into the water, Leptasterias is a brooder. Males release sperm that is somehow acquired by neighboring females and used to fertilize their eggs. There isn’t any space inside a star’s body to brood developing embryos, so a Leptasterias female tucks her babies underneath her oral surface and then humps up over them. Leptasterias also humps up when preying on small snails and such, so that particular posture could indicate either feeding or brooding.

Here’s a Leptasterias humped up on a rock, photographed last spring:

Leptasterias sp. at Pigeon Point.
5 May 2016
© Allison J. Gong

The only way to tell if a Leptasterias star is feeding or brooding is to pick it up and look at the underside. I did that the other day and saw this:

Brooding Leptasterias sp. star at Pistachio Beach.
27 January 2017
© Allison J. Gong

Those little orange roundish things are developing embryos. While the mother is brooding she cannot feed, and can use only the tips of her arms to hang onto rocks. Don’t worry, I replaced this star where I found her and made sure she had attached herself as firmly as possible before I left her. In a few weeks her babies will be big enough to crawl away and she’ll be able to feed again.

Looks like the reproductive season for Leptasterias has begun.

The next day Brenna and I went to Davenport, again hoping to get lucky despite another not-so-low tide and big swell.

Davenport Landing Beach and adjacent rocky areas.
© Google Earth

Davenport Landing Beach is a popular sandy beach, with rocky areas to the north and south. The topography of the north end is quite variable, with some large shallow pools and lots of vertical real estate to make the biota very diverse and interesting. The big rocks also provide shelter from the wind, a big plus for the intrepid marine biologist who insists on going out even when it’s crazy windy. The southern rocky area is very different, consisting of flat benches that slope gently towards the ocean, with comparatively little vertical terrain. The southern end of the beach is always more easily accessible, which is why I almost always go to the north. But this day the north wasn’t going to happen. The winter storms had washed away at least a vertical meter of sand between the rock outcrops. That and the not-so-low tide combined for conditions that made even getting out to the intended collecting site a pretty dodgy affair. So Brenna and I trudged across the beach to the south.

28 January 2017
© Allison J. Gong

Along the way we saw lots of these thumb-sized objects on the beach. At first glance they look like pieces of plastic, but after you see a few of them you realize that they are clearly (ha!) gelatinous things of biological origin. They are slipper-shaped and you can stick them over the ends of your fingers. They have a bumpy texture on the outside and are smooth on the inside.

Any guesses as to what they are?

Pseudoconch of Corolla spectabilis, washed up on Davenport Landing Beach.
28 January 2017
© Allison J. Gong

These funny little things are the pseudoconchs of a pelagic gastropod named Corolla spectabilis. What is a pseudoconch, you ask? If we break down the word into its Greek roots we have ‘pseudo-‘ which means ‘false’ and ‘conch’ which means shell. Thus a pseudoconch is a false shell. In this case, ‘false’ refers to the fact that this shell is both internal (as opposed to external) and uncalcified.

The animal that made these pseudoconchs, Corolla spectabilis, is a type of gastropod called a pteropod (Gk: ‘wing-foot’). Pteropods are pelagic relatives of nudibranchs, sea hares, and other marine slugs. They are indeed entirely pelagic, swimming with the elongated lateral edges of their foot. Like almost all pelagic animals, Corolla has a transparent gelatinous body. Even their shell is gelatinous, rather flimsier than most shells, but it serves to provide support for the animal’s body as it swims.

You can read more about Corolla spectabilis and see pictures and video here.

Why, you may be wondering, do the pseudoconchs of C. spectabilis end up on the beach, and where is the rest of the animal? The body of Corolla and other pteropods is soft and fragile. When strong storms and heavy swells seep through the area, the water gets churned up and pteropods (and other pelagic animals) get tossed about and shredded. This leaves their pseudoconchs to float on currents until they are either themselves demolished by turbulence or cast upon the beach. Corolla is commonly seen in Monterey Bay, and it is not unusual to find their pseudoconchs on the beaches after a series of severe storms.

Brenna and I were wondering if we could preserve the pseudoconchs somehow. I took several back to the lab and tried to dry them, thinking that they might behave like Velella velella does when dried. Unfortunately, the next day they had shriveled into unrecognizable little blobs of dried snot, and the day after that they had disintegrated completely into piles of dust. Maybe drying them more slowly would work. Something to consider the next time I run across pseudoconchs in the sand.