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Earlier this week an acquaintance asked me about the development of sand dollars, specifically if it is anything like that of sea urchins. It just so happens that sea urchins and sand dollars, while not in the same taxonomic family, are in the same class, the Echinoidea. As close kin, they share a similar larval form, the pluteus larva, and undergo more or less the same development. If you're satisfied with the short answer, you can stop reading here.

Interested in the details? Then read on!

In my first year of graduate school I took a course in comparative invertebrate embryology through the University of Washington up at the Friday Harbor Lab in Puget Sound. It was a blast! We spent mornings in lecture and afternoons in the field and/or in the lab observing and drawing embryos and larvae. At night we would lie on our bellies on the dock and shine a light over the water, scooping up the critters that rose to the surface. It was in this class that I did my first studies of larval development and fell in love with the echinopluteus. In that class we studied several echinoid species, but the only one I was able to follow all the way through to metamorphosis was the sand dollar Dendraster excentricus.

Even a casual beachcomber has likely encountered the naked tests of dead sand dollars, but I'd bet that most people haven't seen them alive. The bare test is white, while in life the animal is a fuzzy grayish-purple color. As their name indicates, they live on sandy bottoms in the shallow subtidal, where they prop themselves in the sand and catch particles of food that fall on them. This photo below is of the sand dollar exhibit at the Monterey Bay Aquarium. My friend, Chris Mah, is the owner of the most excellent Echinoblog and has explained how sand dollars really are sea urchins. Check it out for some good information from a real-life echinodermologist (yes, I just made up that word).

Dendraster excentricus, the eccentric sand dollar. © Monterey Bay Aquarium
Dendraster excentricus, the eccentric sand dollar.
© Monterey Bay Aquarium

But the original question I was asked to address is about the development of sand dollars as it compares to that of sea urchins. Given that these animals share the same larval form, you would probably not be surprised to learn that their overall development is very similar. Just to remind myself of exactly how similar, I dug through my old embryology notebook and took pictures of some of my drawings. Keep in mind that these drawings were intended to document my observations, not to be pretty or artistic. However, they may be useful as comparisons with the photos of sea urchin larvae that I've been taking over the years.

Early pluteus larva of Dendraster excentricus (eccentric sand dollar), drawn from life. © Allison J. Gong
2-day-old early pluteus larva of Dendraster excentricus (eccentric sand dollar), drawn from life.
© Allison J. Gong

According to my notes, to speed up development we cultured these larvae at room temperature so we could get through the entire larval period in the 5-week course. I didn't record the temperature, but would guess it to be about 17ºC. At this temperature it took the Dendraster larvae only two days to get to the early pluteus stage, complete with functioning gut and skeletal rods (see drawing on right).

In contrast, the Strongylocentrotus larvae that I started this past January were still forming their guts at the ripe old age of 2 days. You'll have to take my word for that, as I didn't take pictures. I do have a photo of the embryos when they were 1 day old and had just hatched:

1-day-old embryos of S. purpuratus. The empty space inside each embryo is called the blastocoel. 20 January 2015. Photo credit:  Allison J. Gong
1-day-old embryos of S. purpuratus, 21 January 2015.
Photo credit: Allison J. Gong

By the age of 7 days, the Dendraster larvae already had three pairs of fully developed arms (the anteriolateral, postoral, and posterodorsal arms), with the fourth and final pair (the preoral arms) just beginning to form:

7-day-old pluteus larva of Dendraster excentricus. © Allison J. Gong
7-day-old pluteus larva of Dendraster excentricus, drawn from life.
© Allison J. Gong

The Strongylocentrotus larvae, on the other hand, had barely started growing their first arms at 6 days of age:

6-day-old pluteus larva of Strongylocentrotus purpuratus. © Allison J. Gong
6-day-old pluteus larva of Strongylocentrotus purpuratus, 26 January 2015.
© Allison J. Gong

After a few weeks the Dendraster larvae had grown all four pairs of their arms as well as their juvenile rudiment on the left side of the gut. The individual I drew has a fully formed rudiment with five tube feet (labelled 'podia' in the drawing) and an additional waviness to the ciliated band (shaded in the drawing). My guess at the time was that this individual was developmentally competent, or ready to settle out of the plankton and metamorphose.

27-day-old pluteus larva of Dendraster excentricus. © Allison J. Gong
27-day-old pluteus larva of Dendraster excentricus, drawn from life.
© Allison J. Gong

Most of the sea urchin larvae had not even started forming rudiments by the age of 31 days:

31-day-old pluteus larva of Strongylocentrotus purpuratus, 20 February 2015. © Allison J. Gong
31-day-old pluteus larva of Strongylocentrotus purpuratus, 20 February 2015.
© Allison J. Gong

When I was in Friday Harbor I was lucky to see one of my Dendraster larvae undergo metamorphosis more or less as I was watching under a microscope. I wish I'd had the set-up to take microscope pictures, because it was an amazing phenomenon to observe. I did make one last drawing of the newly metamorphosed and benthic tiny sand dollar and its discarded larval skeletal rods:

Newly metamorphosed Dendraster excentricus, drawn from life. © Allison J. Gong
Newly metamorphosed Dendraster excentricus, age 29 days, drawn from life.
© Allison J. Gong

I'm sure that I drew what I saw, but looking at this drawing with more experience I wonder if the tube feet really looked like that. Oh well. One of the last things we did as a class was "graduate" our remaining larvae off the dock and wish them luck as we released them into the real world.

With my most recent batch of S. purpuratus larvae, I began seeing competence at 45 days post-fertilization. The first bona fide juvenile urchin didn't begin crawling around on tube feet until 50 days:

Newly metamorphosed Strongylocentrotus purpuratus, age 50 days. 11 March 2015. © Allison J. Gong
Newly metamorphosed Strongylocentrotus purpuratus, age 50 days. 11 March 2015.
© Allison J. Gong

The next logical question would be: Why do the sand dollars develop so much more quickly than the urchins? I don't have a definitive answer for that. Since that class in Friday Harbor I haven't had another chance to study sand dollars, but in my experience my most recent cohort of sea urchins progressed through development at the normal pace for the species in this location. Some species just take longer than others, and the differences could be due to any number or combination of factors: water temperature, genetics, presence or absence of settling cues, water chemistry, and so on. The take-home message, if you've managed to read this far, is that yes, sand dollars and sea urchins undergo pretty much the same development. It's the same as the short answer at the top of the post, but wasn't it fun getting there the long way?

When I moved to the coast these many years ago and started poking around in the local intertidal, I became entranced with little animals called staurozoans. I can't claim to have been to every intertidal site in the area, but I've been to several of them and I personally know the staurozoans to occur at only two sites: Carmel Point (I've seen them there once) and Franklin Point (I used to see them there fairly regularly). In 2007 I went out to Franklin Point every month that had a negative low tide during daylight hours to monitor the abundance and size of the staurozoans; heck, once I even went out in the dark armed with a headlamp and a friend who was supposed to watch my back but instead fell asleep against the cliff. The staurozoans were easy to find that year and occurred in large numbers.

I used to be able to find the staurozoans in one particular area on the north side of Franklin Point where the water continually swashes back and forth.

Intertidal at Franklin Point, 3 July 2015. © Allison J. Gong
Intertidal at Franklin Point, 3 July 2015.
© Allison J. Gong

The staurozoans would always be attached to algae, often perfectly matching the color of their substrate. I remember seeing two versions, one a reddish brown and the other a vibrant bottle green color, of the same species of Haliclystus.

In March of this year I saw a lot of small staurozoans when I braved the afternoon winds at Franklin Point. The conditions were pretty horrid, with the water all churned up and murky so I couldn't take any pictures, but I was happy to see my little guys because it meant they were there. I hadn't seen them for a few years before this past spring and was beginning to doubt my search image. Huzzah for validating my gut feeling! I may have whooped and done the happy dance in my hip boots that afternoon.

Fast forward almost three months and three additional trips out to Franklin Point before I found a staurozoan this morning. One. And it was only about 0.5 cm tall, the same size that they were in March. And it was brown, the same color as most of the algae out there. Because they live where the water is constantly moving it's really hard to photograph them in situ. This is the best I could do:

Haliclystus sp. in situ at Franklin Point, 3 July 2015. © Allison J. Gong
Haliclystus sp. at Franklin Point, 3 July 2015.
© Allison J. Gong

It's hard to appreciate from this photo just how beautiful these animals are. They are very animated, swaying in the current and although they are attached they can slowly creep over surfaces or even detach, somersault around, and re-attach. Back in the day when I used to find them frequently I brought some back to the lab to observe them more closely. I could get them to feed, but they never lasted more than about a week in captivity.

So, what exactly are staurozoans? They are cnidarians, kin to sea anemones, hydroids, Velella velella, and jellies. Their common name is stalked jellies, and for a long time biologists considered them to be closely related to the jellies in the cnidarian class Scyphozoa. However, recent studies of the genetics of staurozoans have caused taxonomists to elevate these creatures to their own class, the Staurozoa.

Not much is known about the ecology of Haliclystus in California, probably because they are so damn difficult to find in the field. I have one or maybe two more trips out to Franklin Point this summer before we lose the minus tides for the season; hopefully they will still be there. I'd love to get some better pictures of them to show my students this fall. Wish me luck!

1

This spring and summer the local beaches have at times been covered by what appear to be small, desiccated, blue or white potato chips. They would typically be seen in windrows at and just below the high-tide line, or blown into piles. The most recently washed up ones are a dark blue-violet color, while the ones that have been on the beach for more than a day or two are faded to white.

Windrows of Velella velella (by-the-wind sailor) washed up on the beach at Point Piños, 9 May 2015. © Allison J. Gong
Windrows of fresh Velella velella (by-the-wind sailor) and algal detritus washed up on the beach at Point Piños, 9 May 2015.
© Allison J. Gong
Desiccated Velella velella on the beach at Franklin Point, 22 April 2015. © Allison J. Gong
Desiccated Velella velella on the beach at Franklin Point, 22 April 2015.
© Allison J. Gong

These animals are Velella velella, commonly called by-the-wind sailors. Taxonomically they are in the Class Hydrozoa of the Phylum Cnidaria. Other members of this class are the colonial hydroids and siphonophores (such as the Portuguese man-o'-war, Physalia) as well as the freshwater hydras that you may have played around with in high school. Technically speaking, Velella isn't a jellyfish. Actually, if we want to get uber-technical about it, there's no such thing as a jellyfish at all; or if there is, it's a vertebrate (i.e., some kind of actual fish) rather than a cnidarian. Most of the gelatinous creatures that people generally refer to as "jellyfish" are in fact the medusae of cnidarians.

That said, Velella is a special kind of hydrozoan. Its body consists of an oblong disc, 3-10 cm long, with tentacles and such hanging down and a sail sticking up. The little sail catches the wind that propels the animal:

Single Velella velella washed up on beach at Franklin Point, 22 April 2015. © Allison J. Gong
Single Velella velella washed up on beach at Franklin Point, 22 April 2015.
© Allison J. Gong

How do so many of these animals end up on the beach? The answer is that they float on the surface of the ocean and are at the mercy of the winds, hence their common name. This is an extremely specialized habitat called the neuston. Organisms living here have to be adapted to both aerial and marine factors. In fact, the blue pigment in these animals is thought to act as a sunscreen, reflecting the blue (and probably UV) wavelengths and protecting the underlying cells. We all know that UV radiation damages DNA, right? That's why we wear sun protection. Other cnidarian inhabitants of the neuston are things like Physalia and Porpita porpita (blue buttons), which are also blue in color. A former boss of mine used to say that for every hydroid there's a nudibranch that lives on it, eats it, and looks just like it. Porpita isn't exactly a hydroid, but it does have a predatory nudibranch, Glaucus atlanticus, which is (of course) blue-purple! Glaucus eats Velella, too.

Porpita porpita (left) and its predator, the nudibranch Glaucus atlanticus. Diameter of P. porpita approx. 2 cm.
Porpita porpita (left) and its predator, the nudibranch Glaucus atlanticus. Diameter of P. porpita approx. 2 cm.

 

 

 

 

 

 

 

 

The Monterey Bay Aquarium Research Institute (MBARI) has, of course, one of the best video explanations of what Velella is all about. I certainly can't do any better, so you should watch this:

By the way, MBARI's YouTube channel is like marine biology and oceanography porn. Just sayin'. If you have some time to kill on the Internet, you could certainly do worse than to spend it there!

3

This morning I went on a solo trip to one of my favorite intertidal sites up the coast a bit. I've been busy with stuff at the marine lab and my house is a construction zone this summer so it was really nice being alone in nature for a couple of hours before most people had gotten out of bed.

I didn't find what I was looking for but did see some great stuff that I wasn't looking for, which is just as rewarding.

The approach to the beach over the dunes is always spectacular even on a gloomy morning. I find this color palette very soothing.

The hike over the dunes, 5 June 2015. © Allison J. Gong
The hike over the dunes, 5 June 2015.
© Allison J. Gong

The site itself is rocky with a sandy bottom. Depending on the severity of recent storm action there can be more or less sand. Winter storms wash sand away, while in the summer the sand tends to accumulate and can bury the rocks to surprising depths.

Surfgrass bed (Phyllospadix sp.) and rocks at Franklin Point, 5 June 2015. © Allison J. Gong
Surfgrass bed (Phyllospadix sp.) and rocks at Franklin Point, 5 June 2015.
© Allison J. Gong

It may be an optical illusion, but when I'm scrunched down in amongst the rocks it appears that the waves are breaking at heights quite a bit above my head. Most of the water's force is dissipated as the waves wash over the rocks, and unless I've wandered out too far, by the time it gets to me all I need to worry about is whether the surge will overtop my boots. Which has indeed happened and makes for a cold squelchy morning.


And now for some happy snaps!

A small mid-intertidal pool at Franklin Point, 5 June 2015. © Allison J. Gong
An example of intertidal biodiversity at Franklin Point. The most conspicuous organisms are Ulva (sea lettuce), coralline algae (the pink stuff), small acorn barnacles, the tube-dwelling worm Phragmatopoma californica, and small anemones in the genus Anthopleura. 5 June 2015.
© Allison J. Gong
I love my hip boots!  © Allison J. Gong
I love my hip boots!
© Allison J. Gong
Pagurus hirsutiusculus hermit crab in shell of the snail Olivella biplicata, 5 June 2015. © Allison J. Gong
Pagurus hirsutiusculus hermit crab in shell of the snail Olivella biplicata, 5 June 2015.
© Allison J. Gong
A beautifully camouflaged kelp crab (Pugettia producta) hiding in plain sight, 5 June 2015. © Allison J. Gong
A beautifully camouflaged kelp crab (Pugettia producta) hiding in plain sight, 5 June 2015.
© Allison J. Gong

Because, really, doesn't everybody have a favorite red alga? This is mine. It presses gorgeously and is so damn beautiful!

Erythrophyllum delesserioides, 5 June 2015. © Allison J. Gong
Erythrophyllum delesserioides, 5 June 2015.
© Allison J. Gong

At one point I saw a worm-like thing thrashing around in a shallow pool. Turns out it was a polychaete worm, probably in the genus Nereis, doing epic battle with a predatory nemertean worm (Paranemertes peregrina). By the time I figured out what was going on and stuck my camera in the water the interaction had more of less come to an end. The polychaete did get away without apparent damage, but it was moving pretty slowly afterward. In this video Nereis is the segmented worm that's doing all the wiggling, and Paranemertes is the purple and beige unsegmented worm that you can sort of make out in the top of the frame. I wish I had been swifter on the uptake with the camera.


And the pièce de résistance for this trip:  A little sea hare! This guy was so small (about 2.5 cm long) that at first I thought it was a clump of red algae. Then I saw the little rhinophores (those ear-like projections that give them their common name) and recognized it as a sea hare. Amazingly cute!

A little sea hare (Aplysia sp.), 5 June 2015. © Allison J. Gong
A little sea hare (Aplysia sp.), 5 June 2015.
© Allison J. Gong

I was lucky enough to capture some video of this critter crawling around.

Aside from the rhinophores it doesn't look hare-like at all, does it? I wonder about common names sometimes.

All in all, it was a great morning. An early morning low tide is the best reason I can think of to crawl out of bed at 04:30!

Yesterday afternoon when I got home I checked out the red-tailed hawk nest across the canyon and didn't see anybody home. Then I started scanning the trees on both sides of the canyon to see if the parents were around. While I was looking the dad flew in with prey and perched on the top of one of the trees. But he didn't start eating right away so I thought he might have been showing the prey to the kids. Sure enough, we found one of the juveniles perched just a short distance away.

Buteo jamaicensis (red-tailed hawk) father (left) and newly fledged offspring (right), 14 May 2015. © Allison J. Gong
Buteo jamaicensis (red-tailed hawk) adult male (left) and newly fledged offspring (right), 14 May 2015.
© Allison J. Gong

The adult male's plumage is nice and sleek, and he perches quite easily on a branch that sways dramatically in the afternoon wind. The juvenile's feathers are rumpled and its head looks small, probably because it hasn't been feathered very long, and it had some problems with balance.

At some point the juvenile managed to hop over to its dad, who then shared some of his food.

So we knew for a fact that at least one of the juveniles had fledged; however, we didn't find the other juvenile anywhere. We did see the adult female perched atop a tall snag on our side of the canyon; she was looking around but didn't seem worried so we figured that the second juvenile at least wasn't on the ground or in some other danger.

And lo and behold, as the sun was beginning to set and light the other side of the canyon, we found both juveniles and the adult female perched on trees across the way. So both of the kids had fledged successfully!

Buteo jamaicensis (red-tailed hawks), newly fledged juveniles (left and lower right) and adult female (upper right), 14 May 2015. © Allison J. Gong
Buteo jamaicensis (red-tailed hawks), newly fledged juveniles (left and lower right) and adult female (upper right), 14 May 2015. © Allison J. Gong

I don't know what the juvenile on the left is doing and why it appears not to have a head. We still haven't actually seen either of the juveniles flying, but by the time it was getting dark both had returned to the nest for the night. I imagine they slept well after all the day's exertions!

 

4

Our red-tailed hawk chicks are sooo close to fledging now! I've been told that the tree-nesting raptors usually first leave the nest to hop around on branches; hence they're called "branchers." This afternoon I watched the chicks and was able to catch some of the maneuvering, which included hopping around the edge of the nest.

One of the chicks seems more adventurous than the other. I know that female raptors are larger than males, so I think that males reach their fledging size sooner than their sisters. Which would mean that this earnest almost-brancher is a boy. He'll be flying soon!

This morning I took a small group of Seymour Center volunteers on a tidepooling trip to Point Piños (see red arrow in the photo below). Point Piños is a very interesting site. It marks the boundary between Monterey Bay to the right (east) of the point and the mighty Pacific Ocean to the left (west).

Map of Monterey Bay. Red arrow indicates Point Pinos.
Map of Monterey Bay. Red arrow indicates Point Piños.
Point Pinos, 9 May 2015. © Allison J. Gong
Point Piños, 9 May 2015.
© Allison J. Gong

As is my usual habit, we began our exploration on the Pacific side of the point. Almost immediately, Victoria found an octopus! And a couple of meters away, she found another one!

Octopus rubescens at Point Pinos, 9 May 2015. © Allison J. Gong
Octopus rubescens at Point Piños, 9 May 2015.
© Allison J. Gong

As we approach the summer solstice, the algae and seagrasses are at their most lush. Point Piños is a fantastic site for algal diversity; every time I come here I want to take some back with me so I can study it at the lab. Alas, collecting at Point Piños is not allowed even for someone (like me) who holds a valid scientific collecting permit.

Beds of Phyllospadix scouleri at Point Pinos, 9 May 2015. © Allison J. Gong
Beds of Phyllospadix scouleri (surf grass) at Point Piños, 9 May 2015.
© Allison J. Gong
Macroalgae at Point Pinos, 9 May 2015. © Allison J. Gong
Macroalgae at Point Piños, 9 May 2015.
© Allison J. Gong

And yes, that log-like object towards the upper-left corner is a harbor seal (Phoca vitulina). A handful of seals were hauled out on the rocks.

However, I was much more interested in the invertebrates. I wasn't looking for anything specific, but in the back of my mind I was keeping track of certain nudibranchs and looking for small stars.

We did see many Patiria miniata (bat stars) in the 1-2 cm size range. Most of them were a bright orange-red color, but some were beige, yellow, or blotchy. There was one large (bigger than my outstretched hand) Pisaster ochraceus that was intensely orange. And Point Piños is always a good spot to see many of the six-armed stars in the genus Leptasterias.

Patiria miniata (bat star), about 1.5 cm in diameter, 9 May 2015. © Allison J. Gong
Patiria miniata (bat star), about 1.5 cm in diameter, at Point Piños, 9 May 2015.
© Allison J. Gong
Large healthy Pisaster ochraceus (ochre star), 9 May 2015. © Allison J. Gong
Large healthy Pisaster ochraceus (ochre star) at Point Piños, 9 May 2015.
© Allison J. Gong
Leptasterias sp., one of the six-armed stars, 9 May 2015. © Allison J. Gong
Leptasterias sp., one of the six-armed stars, at Point Piños,  9 May 2015.
© Allison J. Gong

In terms of nudibranchs there were many Doriopsilla albopunctata, a yellow dorid with tiny white spots. We saw quite a few of them crawling around on the emersed surf grass, as well as in pools. And of course Okenia rosacea (Hopkins' rose) was there, although not in the huge numbers I was expecting.

Doriopsilla albopunctata at Point Piños, 9 May 2015. © Allison J. Gong
Doriopsilla albopunctata at Point Piños, 9 May 2015.
© Allison J. Gong
Okenia rosasea (Hopkins' rose nudibranch) at Point Piños, 9 May 2015. © Allison J. Gong
Okenia rosasea (Hopkins' rose nudibranch) at Point Piños, 9 May 2015.
© Allison J. Gong

In the low zone I saw a few thalli of the intertidal form of Macrocystis pyrifera, the giant kelp that forms the forests that the California coast is famous for. I'd seen this intertidal form named Macrocystis integrifolia, but it appears that now the two forms (intertidal and subtidal) are both considered to be M. pyrifera. To my eye, the intertidal form differs morphologically by having rounder pneumatocysts (floats) and a holdfast that is less dense than the subtidal form.

Macrocystis pyrifera (giant kelp) growing intertidally at Point Piños, 9 May 2015. © Allison J. Gong
Macrocystis pyrifera (giant kelp) growing intertidally at Point Piños, 9 May 2015.
© Allison J. Gong

Hermit crabs are diverse and abundant at Point Piños. Here's an example of Pagurus samuelis, the blue-banded hermit crab; even when you can't see the blue bands on the legs, the bright red antennae are a major clue to this crab's identity.

Pagurus samuelis (blue-banded hermit crab) at Point Piños, 9 May 2015. © Allison J. Gong
Pagurus samuelis (blue-banded hermit crab) at Point Piños, 9 May 2015.
© Allison J. Gong

When we climbed over the point to the Monterey Bay side, I found two of these little gastropod molluscs, which I didn't recognize. They are about 1 cm long, with a brown lumpy mantle that can covers the shell, which is pinkish in color. After putting it out on Facebook that I needed help with the ID, a bunch of friends and friends of friends chimed in (thanks John, Rebecca, Barry, and David!) and I was able to determine that these little guys are Hespererato vitellina:

Hespererato vitellina (appleseed Erato snail) crawling on Phyllospadix scouleri (surf grass) at Point Piños, 9 May 2015. © Allison J. Gong
Hespererato vitellina (appleseed Erato snail) crawling on Phyllospadix scouleri (surf grass) at Point Piños, 9 May 2015.
© Allison J. Gong

On our way back up the beach we noticed long windrows of Velella velella, the by-the-wind sailors, washed up. While most of them were faded and desiccated, there were enough freshly dead ones that were still blue, which may have washed up on the previous high tide.

Windrows of Velella velella (by-the-wind sailor) washed up on the beach at Point Piños, 9 May 2015. © Allison J. Gong
Windrows of Velella velella (by-the-wind sailor) washed up on the beach at Point Piños, 9 May 2015.
© Allison J. Gong

All in all, a very satisfactory morning. I saw things I expected to see, some things I didn't quite expect but wasn't surprised to see, and some things I'd never seen before. That Hespererato vitellina was completely new to me, which is always exciting.

Next up:  What kinds of things live in white calcareous tubes?

Most of the animals that we are familiar with (think of any pets you've ever had) have bilateral symmetry: they have a head end and a tail end, a left and a right, and a top and a bottom. In scientific terms that translates to the anterior-posterior, left-right, and dorsal-ventral axes. Also, most bilateral animals are elongated on the anterior-posterior axis and have some sort of cephalization going on in the anterior end of the body; in other words they have a head, or at least a concentration of neural tissue and sensory structures in the part of the body that encounters the environment first.

Even your basic worm meets all these criteria. Here's a video clip of Nereis sp., an intertidal polychaete worm. The body is conspicuously segmented, as this animal is a somewhat distant relative of earthworms. The body symmetry is clearly bilateral, and you can see that it has an anterior end, which in this case is defined by both the direction of locomotion and the presence of a head:

As "normal" as bilateral symmetry may seem, there are many animals that have a completely different type of symmetry. The cnidarians, for example, are the largest group of animals with radial symmetry. This means that instead of being elongated along an anterior-posterior axis, these animals' bodies are either columnar or umbrella-shaped. In either case, when you look down on them you see a circular shape:

Anthopleura sola, photographed at Natural Bridges State Beach © Allison J. Gong
Anthopleura sola at Natural Bridges State Beach
© Allison J. Gong

An animal with this sort of body plan obviously has no head--no eyes, nose, or concentration of either neural or sensory structures. Being a sea anemone, it lives attached to the sea floor and doesn't walk around much, so there's also no locomotory clue as to a possible anterior end, either. Rather than have most of its neural apparatus located in a particular region, its nervous system is diffusely scattered over the entire body. This animal has the advantage of meeting its environment from all sides and across all of its external surface. It can't be snuck up on, because it has no front or back.

Let's now return to the echinoderm pentaradial symmetry. As you might imagine, the five-way symmetry of echinoderms has strong implications both for other aspects of the animal's anatomy and the way that it interacts with its environment.

Take the example of a sea star:

Dermasterias imbricata at Pigeon Point, 18 January 2015. © Allison J. Gong
Dermasterias imbricata at Pigeon Point, 18 January 2015.
© Allison J. Gong

Echinoderms are structurally more complex than cnidarians, with distinct internal organs. The central disc contains most of the organs, but there are extensions of both the gut and the gonads in each of the five arms. Although, like the cnidarians, the echinoderms don't have a centralized nervous system, they do have very simple eyes that can detect light and dark. And guess where, in an animal with a form of radial symmetry, the eyes are located? Hint:  Think about how the animal encounters its environment. Yes, the eyes are in the tips of the arms, along with chemosensory receptors. Makes sense, doesn't it?

Pentaradial symmetry also affects how an animal locomotes. Since they have no front or back, sea stars and sea urchins can walk in any direction. They can also change the direction of locomotion easily, without needing to turn around the way we would.

There's a natural human tendency to regard creatures like us as somehow better than those different from us. I try to teach my students that complex is not always better (think of the pervasive damage done to a person who has suffered a major brain or spinal cord injury); that there are multiple types of complexity (morphological, behavioral, reproductive, and life cycle); and that the best way to understand an animal is to put yourself in its "shoes" and try to imagine what its life is like, with its anatomy, physiology, and lifestyle. It can be difficult to shed our human-centric biases, but we have to put them aside at least temporarily if we truly want to make sense of what's going on in the world around us.

3

Anybody who has visited one of the sandy beaches in California has probably seen kids running around digging up mole crabs (Emerita analoga). These crabs live in the swash zone at around the depth where the waves would be breaking over your ankles, moving up and down with the tide. They are bizarre little creatures, burrowing backwards into the sand with just their eyestalks and first antennae reaching up into the water.

Although it's called a mole crab, Emerita's external anatomy isn't very similar to that of other crabs. For one thing, it doesn't have claws. In fact, its legs are quite unlike the legs that you'd see in a typical crab. Check out Emerita's appendages:

External anatomy of Emerita analoga
External anatomy of Emerita analoga

The crab's head faces to the left in this diagram. The real surprise that these little crabs hide is the nature of the second antennae. Usually the crab keeps these long, delicate antennae protected under its outer (third) pair of maxillipeds. This is why you don't see them when you dig up a mole crab.

You do see them when the crabs are feeding. As a wave washes over the crab, it extends the second antennae and pivots them them around on ball-and-socket joints. The feathery antennae catch particles in the water, then are drawn underneath the maxillipeds so the food can be slurped off and eaten.

Here's a top-down view of two Emerita feeding. The purple-grayish thing in the field of view is a sand dollar (Dendraster excentricus).

This side view gives a better angle of what's going on:

I find these little crabs quite captivating. I love how they rise up when I put food into their tank.  Watching them feed always makes me smile.

3

As a native Californian, I've been living with drought my entire life. Well, maybe not so much during the El Niño of 1997-98, but even then the thought "We have water now but might not later..." was always in the back of my mind. This season we had a great few weeks of rain in late November and early December, then January was bone dry and February has been disappointing as well.

This weekend an Arctic storm is moving through the region, bringing rain and cool temperatures to coastal areas and (hopefully) snow in the Sierra Nevada. Here in Santa Cruz it hasn't rained much yet but we did get a few decent showers this morning. It just so happened that I headed down to the marine lab between showers, and the light was magnificent. The water was that magical color of aquamarine and seaglass green that I associate with the tropics. The sun was shining, casting cloud shadows on the water, which added depth to the color palette when combined with the kelp bed. So pretty!

Looking east towards Natural Bridges from Terrace Point, 28 February 2015. ©Allison J. Gong
Looking east towards Natural Bridges from Terrace Point, 28 February 2015.
© Allison J. Gong
See how translucent and green the water is? 28 February 2015. ©Allison J. Gong
See how translucent and green the water is? 28 February 2015.
© Allison J. Gong

Brown pelicans (Pelicanus occidentalis) were one of many bird species whose populations were devastated by widespread use of the pesticide DDT in the mid-20th century; in 1970 it was listed on the federal Endangered Species List. After the general use of DDT was banned in the United States in 1972 the population began to recover, and in 2009 the brown pelican was removed from the Endangered Species List (I believe the bureaucratic jargon for that is "de-listed"). It is now not unusual to see long lines of pelicans skimming the waves as they fly just above the ocean surface.

Today I didn't see any large groups of pelicans in flight, but I did catch this one flying by right in front of me.

Brown pelican (Pelecanus occidentalis) flying past Terrace Point, 28 February 2015. ©Allison J. Gong
Brown pelican (Pelecanus occidentalis) flying past Terrace Point, 28 February 2015.
© Allison J. Gong

Anyone who knows me personally knows that I'm not a big cheerleader for the marine mammals. However, seeing cetaceans in the wild is always a treat. This morning I was lucky enough to catch this pod of dolphin-type critters as they swam right off the point. There were 6-8 of them, I think. As they swam past the marine lab a couple of them indulged in some tail slapping.

Dolphins swimming past Terrace Point, 28 February 2015. ©Allison J. Gong
Small cetaeans swimming past Terrace Point, 28 February 2015.
© Allison J. Gong

I'm not enough of a cetacean expert to be able to identify the animals from photos. They did have dolphin-like dorsal fins but I couldn't see a prominent rostrum on any of them. I didn't have my binoculars with me . . . and I call myself a naturalist??

Since the animals were not traveling very quickly I decided to see if I could catch them on video. I was lucky enough to get this clip:

Can anybody help me identify what these animals are?

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