DEUTEROSTOMIA, ECHINODERMATA I
(Echinoderm study images;
1) The DEUTEROSTOMIA form the second major branch in the Tree of Life; they share several traits: radial, indeterminate cleavage, mesoderm from epithelial cells, coelom via enterocoely, blastopore yields anus, tripartite coelom and body plan, monociliated cells
2) Phylogenetic relations among them remain hotly debated!
1) The ECHINODERMATA ("spiny-skinned animals") approx. 6,000 living spp; an ancient, solely marine phylum of approx. 20 classes, but only 6 living!
2) Most bizarre of all living animal phyla: "I salute the echinoderms as a noble group designed to puzzle the zoologist" (L.H. Hyman 1955)
3) Five main living classes: CRINOIDEA (feather stars, sea lilies; ~75 spp.), ASTEROIDEA (starfish; ~1,500 spp.), OPHIUROIDEA (brittle stars; ~2,000 spp.), ECHINOIDEA (sea urchins, sand dollars; ~950 spp.), HOLOTHUROIDEA (sea cucumbers; ~1,200 spp.)
4) Pentaradial symmetry was linked to a sessile lifestyle (primitively)
5) Though phylogenetic relations are still debated, 2 body plans prevail:
Copyright (c) 2013 by A. Richard Palmer. All rights reserved.
(revised Jan. 3, 2013)