If anyone remembers, 2015 was a year of strange weather. The Blob of warm water in the northeast Pacific governed weather patterns throughout California, and we had an unusually warm and sunny summer, with none of the normal fog on the coast. Nature's air conditioner went on the fritz that year.
Since I spent most of 2016 in the mental fog of concussion I'm not sure I can recall with any accuracy whether or not last year was a normal year. So far 2017 feels like a return to old times, at least in terms of the intertidal biota. I've seen fewer of the species that creep up the coast during El Niño, such as the pink blobs of bubble gum called Hopkins' rose, which were spattered everywhere in 2015. The algae are lusher than I've seen in what feels like forever, but was probably only about three years.
All this to say that things seem to be returning to normal, and I want to show off some pictures I've taken so far this season.
First up, Dictyoneurum californicum, a kelp. As the blades mature they split down the middle near the holdfast.
Both species of surfgrass seem to be doing well, too. The two species, Phyllospadix torreyi and P. scouleri often grow side by side in the exact same spot. Just the other day I saw the season's first flowers on P. scouleri at Pigeon Point.
The two species of Phyllospadix can be distinguished by the shape of their leaves. Phyllospadix torreyi's leaves are narrow and sometimes cylindrical in cross-section, while P. scouleri has flatter, more ribbon-like leaves. Phyllospadix scouleri can also be a darker bluish-green color, compared to P. torreyi's brighter spring green color.
At Pistachio Beach I saw that P. scouleri has started to bloom. In one patch I found some fresh flowers, and in the stiller pools the water was covered with a yellow film that I think is the pollen.
When the growing is good, the algae recruit to any available surface. This includes the thalli of established algae, or the bodies of animals. Any surface will do, and the hard shells of molluscs are often fouled by algae and/or small animals.
The mossy chiton, Mopalia muscosa, seems to be especially susceptible to fouling by algae. Or, it could be that it tolerates or even benefits from the population of algae growing on its shell plates. Whatever the reason, M. muscosa often carries more algae around than the other chitons.
Even the owl limpets aren't immune to serving as substrate for other organisms. Here's a large limpet sporting a collection of acorn barnacles, smaller limpets, and a jaunty off-center cap of red algae.
Here's another Mopalia muscosa, supporting at least four species of red algae on its shell plates:
I've been seeing lots of echinoderms in the intertidal, too. The globular ones and the star-shaped ones, at least. Sea urchins (Strongylocentrotus purpuratus) seem to be more common than they have been in recent years, and we are having a bumper crop of the six-armed stars in the genus Leptasterias. Just the other day I saw a Leptasterias star that was brooding her babies:
And brittle stars!
Brittle stars are notoriously difficult to photograph, as they are extremely active and do not like the light. As soon as you get one situated for the camera, it starts crawling around to the back side of whatever you place it on. They aren't happy unless they are safely hidden in the dark. This one, recorded in July 2015, was cooperative only because I didn't really disturb it; I got lucky and happened upon it in deep enough water that I could dunk the camera without having to move the animal.
Good times out there! I hope this apparent return to cold-water flora and fauna sticks. It's totally worth freezing on a damp, drizzly morning, to see the intertidal looking so vibrant and healthy. Cold water is good, productive water!
It seems that most years, the Memorial Day weekend brings some of the lowest spring tides of the year, and 2017 certainly fits the bill. I've been out for the past two days, heading out just as the sun is starting to rise, and already I've seen enough to whet my appetite for more. And with plans for the next few days, I'm pleased to say that my dance card is completely full for this tide series. There are a lot of stories building out there!
At this time of year everything is growing and reproducing. Many of the larvae I've seen in the plankton have parents that live in the intertidal; makes sense that those parents should be having sex now. Barnacles, for example, copulate when the tide is high. I've seen them go at it in the lab, but never in the field, as they don't mate while emersed. This morning I interrupted a pair of isopods locked in a mating embrace, and they swam off, still coupled together, when I disturbed them. Other animals were much less shy. Lifting up a curtain of Mazzaella to see what was underneath, I spotted a small group of dogwhelks (small, predatory snails). I can't be certain, but suspect they were having an orgy.
A short distance away I found the inevitable result of the dogwhelk orgies.
Each of those urn-shaped objects is an egg capsule, containing a few dozen developing embryos. After the snails copulate the mating individuals go their separate ways. The females lay these egg capsules in patches in the mid-intertidal, usually on a vertical surface under the cover of algae to minimize the risk of desiccation.
For many years now, some of my favorite animals have been hydroids. I worked in a hydroid lab as an undergraduate, and this is when I fell in love with the magic of a good dissecting microscope. A whole new world became visible, and I found it easier than I ever imagined to fall under the spell of critters so small they can't be seen with the naked eye. I still do.
Hydroid colonies come in a variety of forms, shapes, and colors. Most of them are small and cryptic, resembling plants more than any 'typical' animal, and aren't easily seen unless you're looking for them. One intertidal species, however, is pretty conspicuous even to the casual tidepool visitor or beachcomber. It often gets torn off its mooring and washes up on the beach.
A hydroid colony is the benthic polyp stage of the standard cnidarian life cycle. The polyp represents the clonal phase of the life cycle and reproduces by dividing to make several copies of itself. In a colony such as a hydroid, the polyps remain connected to each other and even share a common digestive system. The polyps don't reproduce sexually. That function is reserved for the medusa stage of the life cycle. Some hydroid colonies produce free-swimming medusae, and others hang onto reduced medusa buds or structures so un-medusa-like that they're called gonangia. Aglaophenia is a hydroid that houses its sexual structures in gonangia that are located on the side-branches of the fronds.
Here's a closer view of a single frond of the Aglaophenia colony. I had to bring it back to the lab to look at it under the scope.
The gonangia look like leaves, or pages of a book, don't they? After working a low tide I'm always hungry, and when the lows are early in the morning I'm often cold and sleep-deprived as well. That's my excuse for not dissecting open one of the gonangia to see what's inside.
Even the algae are getting into the act of reproducing and recruiting. This spring I've noticed a lot of baby bullwhip kelps (Nereocystis luetkeana). Nereocystis is one of the canopy-forming kelps in subtidal kelp forests along our coast, but every year some recruit to the low intertidal. However I don't remember seeing so many baby Nereocystis thalli in the tidepools. The smallest one I saw this morning had a pneumatocyst (float) the size of a pea! In mature thalli, the float might get as big as a cantaloupe.
Nereocystis doesn't usually persist or get very large in the intertidal. It is more common to see detached thalli washed up on the beach than to see a living bullwhip kelp longer than about 2 meters in the intertidal. Whether or not this particular nursery area results in an established population remains to be seen. I'm betting 'No' but could very well be proved wrong. Only time will tell.
Did you know that California has a state lichen? I didn't either, and it turns out that we've had one for over a year! In January of 2016, California became the first state to adopt an official state lichen, and Ramalina menziesii joined the ranks of the California poppy (Eschscholzia californica), the California quail (Callipepla californica), the coast redwood (Sequoia sempervirens), and the extinct-in-the-wild California grizzly bear (Ursus californicus) as official symbols of the Golden State.
Lichens are strange beasts, resulting from a symbiosis between two very different organisms, an alga (or in some cases a cyanobacterium) and a fungus. They are photosynthetic like plants and algae thanks to the algal/cyanobacterial partner in the symbiosis, but do not have roots or leaves. The fungus component restricts them to places where fungi can live, which means you generally don't find lichens in very dry places. That said, some lichens have adapted to live in hostile habitats such as the Arctic tundra and arid deserts. Many of them live on trees and other plants, but when they do so they are not parasitic. They can grow on nonliving surfaces such as rocks, buildings, and soils. Lichens are crucial players in the ecological process of primary succession, which occurs when virgin habitat is newly opened up to colonization by life (for example, the area left scoured by a retreating glacier, or land formed by recent lava flowing into the sea). The fungal partner of a lichen sends out hyphae which burrow into rock, eventually weakening it and forming soil. Plants cannot take root until soil is present, so lichens, in addition to being among the first organisms to colonize an area, modify the habitat to enable other species to become established.
In some ways, the fungus partner of a lichen can be viewed as a farmer, in the sense that it houses photosynthetic symbionts that do the hard work of fixing carbon into molecules such as sugars, which can then be used to fuel the fungus's metabolism. The fungus doesn't just mooch off its symbionts, though. As in other symbiotic relationships between unicellular algae and multicellular hosts, the fungus provides a safe place for the algae to live, as well as a stable environment in which to carry out its photosynthetic magic.
Most lichens have a simple morphology, growing as a crust over the substrate. Ramalina menziesii has a lacy morphology and typically lives as an epiphyte, draping over the branches of trees and shrubs. It is often associated with oak trees in California, especially the Coast Live Oaks (Quercus agrifolia) that live in the more humid regions along the coast. During the drought there was much less Ramalina hanging from the thirsty oak trees, but this year there does seem to be more of it. Strands of R. menziesii are used as nesting material by many birds, and I've seen deer eating whole gobs of the stuff, pulling it off the trees with their rubbery lips.
Ramalina menziesii is often referred to as "Spanish moss" which is misleading on any number of counts. First of all, it's not Spanish, being a species native to the west coast of North America. Second, it's not a moss; mosses are plants, and Ramalina is a lichen. Third, there is a true flowering plant (a bromeliad, actually, not a moss at all) with the common name Spanish moss that lives as an epiphyte in the warm humid southeastern U.S. as well as other tropical areas; clearly, this is not the same organism as R. menziesii, although the two may share superficial similarities such as overall growth form and color. If R. menziesii requires a common name for people to understand what it is, then let that name be something descriptive and biologically accurate, such as "lace lichen"; I've seen this name on a few websites and like it.
Lichens and fungi comprise a large part of my body of ignorance regarding the natural history of California. I find them very interesting but inscrutable, and they don't speak to me as loudly as do my beloved marine invertebrates. What this means is that I have a lot of learning to do, and this is always a Good Thing.
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.
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.
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.
The Seymour Marine Discovery Center is currently hosting a satellite reef of the Crochet Coral Reef project. Back in the fall, about 350 UC Santa Cruz students and community volunteers began crocheting creatures real and fanciful with yarn and other materials. Satellite reefs have been built all around the world, in this project that unites mathematics, marine biology, conservation, and a love of working with yarn.
Since this isn't my brainchild I'm not going to go into the background and philosophy of the Crochet Coral Reef project. Instead, I'm just going to show you some photos of the Santa Cruz satellite reef, and encourage you to come see it for yourself. If you happen not to be in the Santa Cruz area, you can click here to find other satellite reefs around the world. You may even want to start your own reef! Note that many satellite reefs are located quite far inland--Colorado, Indiana, Minnesota--so don't let your lack of a nearby ocean keep you from organizing and building your own reef.
Some of the creatures on the reef are made of garbage or plastic, to remind viewers that the world's oceans continue to pay the price for human excesses. This jelly, below, has oral arms made from plastic grocery bags.
And see what familiar object was used for this crab's eyes?
There are multiple species of octopus on this particular reef!
The reef will be on display through October 2017. If you're in the area before then, swing by and check it out!
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.
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.
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.
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.
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 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.
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:
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.
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!
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?
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.
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:
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:
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.
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.
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.
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.
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:
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.
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)?
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 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.
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.