Sea urchin

Taxonomy

Sea urchins are members of the phylum Echinodermata, which also includes sea stars, sea cucumbers, brittle stars, and crinoids. Like other echinoderms they have fivefold symmetry (called pentamerism) and move by means of hundreds of tiny, transparent, adhesive "tube feet". The symmetry is not obvious in the living animal, but is easily visible in the dried test. "Echinodermate" means "spiny skin" in Greek.

Specifically, the term "sea urchin" refers to the "regular echinoids," which are symmetrical and globular. The term includes several different taxonomic groups: the order Echinoida, the order Cidaroida or "slate-pencil urchins", which have very thick, blunt spines, and others. Besides sea urchins, the class Echinoidea also includes three groups of "irregular" echinoids: flattened sand dollars, sea biscuits, and heart urchins.

Together with sea cucumbers (Holothuroidea), they make up the subphylum Echinozoa, which is characterized by a globoid shape without arms or projecting rays. Sea cucumbers and the irregular echinoids have secondarily evolved diverse shapes. Although many sea cucumbers have branched tentacles surrounding the oral opening, these have originated from modified tube feet and are not homologous to the arms of the crinoids, sea stars, and brittle stars.

Tuesday, July 27, 2004

Underwhelmed, for the most part, with today's convention speeches. Barak Obama, US Senate candidate from Illinois, was very good, not as good as Clinton or even Edwards, but still very good. Ron Reagan's speech on stem cell research was an interesting change of pace, but no one in America watched it.

Andrew Sullivan said it best yesterday:
I think [Bill Clinton] was better last night than at either of his own conventions and certainly better than any of his SOTUs. He performed a brilliant rhetorical trick: he deployed the usual canards used against him to buttress Kerry. Rather than attack the wealthy as recjpients of tax cuts, he attacked himself as a now-wealthy man. And then the coup de grace: he put himself and Bush in the same camp as draft-dodgers, in stark comparison to the patriotic Kerry! My jaw was on the floor at that point in a mixture of admiration and horror. But it was mighty effective. And the way in which he described the cost of the tax cut in terms of squandered attempts to improve homeland defense was another smart move. Use the Republican tax cut issue against the Republican security issue. Wedge against them for once. If the constitution didn't prevent it, the man would still be president. After last night's speech, you can see why.