Echinoderms are marine animals recognizable by their (usually five-point) radial symmetry. Echinoderms include starfish, sea urchins, sand dollars, and sea cucumbers, and crinoids (sea lilies). Echinoderms are found at every ocean depth. The phylum contains about 7000 living species. There are no known freshwater or terrestrial species. They are one of the groups of organisms that successful proliferate in the deep-sea environment.
Crinoids have “flower-like” crowns that filter plankton. The crowns are connected to stocks attached to the solid sea floor (making them “sessile” organisms). Other echinoderms are mobile, capable of moving to avoid prey, seek prey, or adapt to changing conditions on the seafloor.
Most echinoderms appear to have a “five sided” or pentagonal or star-shaped appearance (it is really bilateral symmetry). Sand dollars and sea biscuits have small spicules similar to sea urchin spines. They use them to move and to work food toward their mouth-like openings.
Echinoderms first appear in abundance in the early Paleozoic Era. Echinoderms have ossified skeletons (composed of calcium carbonate), and contributed massive amounts of biogenous sediments to many of the world's ancient massive limestone deposits.
|Figure 15.53. Urchin||Figure 15.54. Crinoid||Figure 15.55. Starfish||Figure 15.56. Brittle Star|
|Figure 15.57. Sea cucumber||Figure 15.58. Sand Dollars||Figure 15.59. Crinoids||Figure 15.60. Sea Biscuit|