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The Daily Bucket is a regular feature of the Backyard Science group.  It is a place to note of any observations you have made of the world around you.  Rain, sun, wind...insects, birds, flowers...meteorites, rocks...seasonal changes...all are worthy additions to the bucket.  Please let us know what is going on around you in a comment.  Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
Salish Sea, Pacific Northwest                                                         October 2013

The shorter days of autumn are slowing photosynthetic activity in the bay. Today daylight fuels the phytoplankton nearly 5 hours less than in midsummer, and the sun gets only about half as high in the sky. Less solar energy means less planktonic food for hungry growing invertebrate larvae..I'm finding less stuff in my plankton net these days. I was losing hope of finding any baby echinoderms - like seastars, sea urchins, sea cucumbers, sand dollars - but I got lucky a couple of days ago! This little fellow is a late-stage larval Brittle Star, also known as a Serpent Star. Both good names, you'll see why.

brittle star larv
Echinoderms are a strange group of animals in many ways, and strangers to most of us since they live exclusively in the ocean - even fresh water will kill them. But I see these varied creatures when scuba diving by the tens and hundreds deep under water, hunting, grazing, waving their fronds in the currents, sifting through the sand, hiding in sponges...quite abundant. Occasionally you might see one partly above the surface from the shore, but only if it has a way of keeping wet, having neither waterproof skin nor a solid shell, like a mollusk or crustacean.

Perhaps the strangest feature of echinoderms is that they have no head or brain, and yet are capable of clearly purposeful coordinated action. This is especially odd since they start out their life like most of us animals, with a front end that's always pointed in the direction they are going. The larva in the microphoto above would be swimming toward the larval snail (if both weren't confined between a slide and coverslip). Why? It's mouth is between those rigid front arms, scooping up phytoplankton as it glides through the bay, propelled by many tiny hairs beating in formation.

This little guy is starting to metamorphose, its arms softening and rounding. After most of the year swimming freely in the bay, the larva will discard these straight arms, settle to the bottom - mouth downward - and grow a whole new body. A radially symmetrical body, circular in form, with no front or back, no left or right sides, and no centralized brain and senses. Most of that round central section is filled with stomach, and a mouth of 5 jaws is underneath.

It can move though, as this hand-sized red Star did.

More Serpent Star~Brittle Star action below:

I found this individual (can't say he or she, those parts are hidden inside the body!) while peeking under a rock at very low tide on the sandy/gravely/muddy beach of Aleck Bay. To get a photograph, I picked it up carefully and placed it on this white rock, for contrast. Very carefully! These creatures have a survival strategy: if feeling threatened, they will voluntarily break off an arm or two, which may twitch for a while distracting a predator, while the Brittle Star escapes. Some lizards do this too, with their tail. A new arm will regenerate within a few months.

As soon as I put it down on the surface, it began to crawl down the side of the rock toward the wet sand.

It has many short spines ("Echinoderm" = "spiny-skinned") on its arms for traction. Inside each arm is a series of articulated "vertebrae" with ball-and-socket joints, and muscles running the length.

See the arms waving in the air? They are covered with tube feet, which taste and feel the world around them. It knows which way to go, back to the wet cool sand in a rock crevice, where it's dark has no eyes, but its skin can sense light. Nerves carry information up to a nerve-ring in the center of the body, then - somehow - directions on what action to take back into the arms. There it goes, into the crack between the white rock and the green rock.

How does it steer itself in that direction, if all the arms are the same? In any given moment, one arm will lead. The tip of one arm is broken off...that looks like the "leading" arm to me. But then it changes direction. A different arm takes the lead, launching off onto the next rock over, checking out the prospects not to go that way, and slips back into the crack beside the white rock. I've lost track of which arm is "forward"!
All this took about 10 minutes, according to the date stamps on my photos. Not too slow for an invertebrate, right? But they are actually much swifter-moving in water, their usual habitat. Here's a video of several fighting over a piece of dead shrimp. Now you'll see why they are also called Serpent Stars. The majority of Serpent Stars are scavengers of detritus at the bottom of the sea, like these. They will snag bits of organic material with the tube feet on their serpent-like arms and transfer the food into their mouth. They can be very competitive!

See how they change direction, leading with a different arm? Yet clearly purposeful, and effective in getting the job done.

How do they do that? I don't know. Plants frequently have radial symmetry, but it's very rare in animals. Something to think about.

A note on identification: My red Star on the beach is Ophiopholis kennerlyi, its new name as of 2007. Before that it was considered a form or variant of Ophiopholis aculeata, the Daisy Brittle Star, which is how it appears in Ricketts (Between Pacific Tides) and Light's Manual.

And here's a cool Echinoblog, with pictures of Serpent Star teeth, and more!


Observations for the day from your backyard? Seeing life change form, or change direction? Cool adaptations? Any and all reports are welcome.


And remember -

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Originally posted to Backyard Science on Sat Oct 12, 2013 at 06:30 AM PDT.

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