PHYLUM ECHINODERMATA -- STEMMED VARIETIES
The echinoderms (Greek = "spiny skins") include nearly 20 classes, most of which are extinct, and were never terribly diverse. Many of these classes primarily include animals that attached themselves to the substratum by a flexible stem made of stacked, small calcite disks. All but one of these classes were extinct by the end of the Paleozoic. The exception (Class Crinoidea -- Latin = "lily") is still around today, but even it was far more diverse in the Paleozoic than it ever has been since.
The first photograph is of a small Late Silurian or Early Devonian species from eastern West Virginia (Protaxocrinus virginiensis). The stem, at the bottom. attaches to the base of the calyx, the ~0.5 cm part (that appears to be roughly triangular in the photo) where all the organ systems were contained. The uppermost half of the specimen in the photo is the "arms", flexible feather-like appendages that were used for gathering food. Live crinoids spread these arms out radially, and are often brightly colored, reminding early students of the flowers for which they are named. The scale bar is 1cm. (Photo by B. Carter.)
The next photograph shows the calyx (at bottom) and arms (most of the specimen) of an unidentified crinoid from Mississippian rocks near Huntsville, AL. The scale bar is 1cm. (Photo by B. Carter.)
The third photograph shows ?Aphelacrinus mundus from the same locality. The lowest ~1cm is calyx, the rest is arms, broken off at their distal ends. The scale is 1cm. (Photo by B. Carter.)
The next photograph shows segments of stems from several species of stemmed echinoderms. Some are most likely crinoids, but the smaller ones may belong to other groups. Scale bar is 1cm. (Photo by B. Carter.)
One other fairly common Paleozoic taxon of stemmed echinoderms is the Class Blastoidea. The calyx of blastoids was different from that of crinoids. There are obvious pointed respiratory structures on the sides, and the tiny arms are almost never found attached. The next picture shows two calyces of a common Mississippian blastoid, Pentremites sp. from near Monteagle, TN. The lower specimen has been crushed, slightly, and so is a bit misshapen. The stem attached to the small bump on the lower portions of the specimens. The scale bar is 1cm. (Photo by B. Carter.)
The echinoderms usually have a five part, nearly radial symmetry. In the crinoids there are five arms, in the blastoids there are five of the respiratory structures. The five-fold symmetry will be more obvious in the echinoderms on the next page.