Amazing Nature: The lesser-known marine stars

A Basket star, left, two sea lilies, right, and a brittle star, bottom. (Switgard Duesterloh photo)

Unless one is genuinely interested in the very wonders of life and its many forms, there is little reason to learn about sea stars and some of their relatives; they are not edible and there are no commercial uses for them, except perhaps as decorations in art projects. I repeat myself in describing that sea stars are classified as echinoderms, along with sea urchins, sea cucumbers, sand dollars and a few others.

Of the creatures in this class, only the sea urchins and sea cucumbers are of interest to specialized fisheries. However, it is the “others” that I wanted to discuss in this article.

If you have recently been to the touch tank on Near Island or if you are an avid tide pool observer, you may be familiar with brittle stars.

These are a relative of the sea stars that inhabits the ocean bottom, where it lives in or on top of the sand or mud, or squeezes into small nooks and crevices between rocks. Some species are specialized to partner up with other animals like coral or sponges and attach to them, eating off any particles that fall down from the surface or get carried along by the currents, thus keeping their hosts clean. In these partnership living arrangements, the brittle star often has taken on the same colors as its host, so it can hide in plain sight.

Brittle stars got their name because of the tendency of the arms to break off. This is in fact a defense mechanism. Better to lose an arm than to be eaten, especially if you can easily grow the arm back! Unlike sea stars, brittle stars can grow into two new individuals when damaged, as long as enough of the central disc remains in each.

Most of us rarely see the members of a subgroup of the brittle stars called basket stars. These have a central disc like the brittle stars and their strong arms are branched. As a small group of commercially unimportant animals, they receive little attention, though they are pretty in the way their arms curl and spread into the current as the animals feed at night on anything that is carried on the current.

While I was researching basket stars online, my computer determined I was, in fact, looking for basketball stars and provided a much longer list of links on that topic.

Though similar on first sight, basket stars are not in the same order as the sea lilies or feather stars, which have a stalk and attach themselves to the bottom. In the case of feather stars the adult animal eventually takes off to swim freely, while sea lilies remain attached.

I remember first hearing of this group (Crinoidea) from my father who had a collection of rocks and fossils in a glass vitrine in our house. I was curious about the little circular patterns fossilized in the rock, and he explained that they were the broken off stalks of sea lilies. There are about 200 known forms of sea lilies today, but fossil records show that they were much more numerous in the past.

A more recent development in the echinoderms and one described for the first time as recently as 1986 are the sea daisies.

I admit that until a few minutes ago I had never read or heard of them. These small (about 1cm) animals live in sunken wood at the bottom of the ocean. They share the oral disc, vascular system and little tube feet of the echinoderms, but have no arms like the other members of the group. So far, three species have been found: one in the Bahamas, one in the Northern Central Pacific and one near New Zealand.

It just goes to show that whether we explore the far reaches of space or the ocean depths of our own planet, there are still new stars to discover!

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