ECHINODERMATA, echinus corium,) Fr. Echinodermcs. A class of invertebrate animals belonging to the di vision Radiata or the Cycloneurose sub-king dom. The most familiar examples of them are the common sea-urchin and star-fish.
In these the skin is covered with prickles, a circumstance from which the class has received its name ; but animals of corresponding in ternal structure, such as the Holothuria, are also comprehended among the Echinodermata, although the skin is destitute of prickles. They are all inhabitants of the sea, examples of them are found in all climates, and the remains of extinct species exist in a fossil state in various mineral strata.
Naturalists are not agreed as to the limits of this class. Cuvier includes in it two orders of animals; the first provided with tubular retractile organs named feet, the second desti tute of feet, but allied, he conceives, to the first in other respects. Other zoologists separate this second order of Cuvier from the Echinoder mata. But in fact these apodous animals, comprehending the genera Molpadia, Minyas, Priapulus, and Sipunculus, are as yet so im perfectly known, at least as regards their in ternal structure, that naturalists seem at a loss to discover their appropriate place in the zoo logical system. In these circumstances we shall confine ourselves to the consideration of the true or pedicellate Echinodermata, of whose systematic arrangement the following is a tabu lar view.
Order I. ASTEROIDEA or STELLE RIDA.
Body depressed, divided into rays like a star, or at least with prominent angles. Mouth inferior, generally no anus.
a. Holes for the feet disposed in grooves on the inferior surface.
Genus 1. ASTERI AS, (figs. 298 vol. i. 7-22.) b. No grooves for the feet.
Genus 2. OPIII URA. Rays simple, elon gated, cirrhous, with lateral spines. Genus 3. EU RYA LE. Rays long, cir rhous, divided dichotomously.
Genus 4. COM ATULA . Rays in two sets, dorsal and marginal. The dor sal rays simple, filiforni, cirrhous. The marginal much larger and pin nated, their inferior pinnules turned downwards and surrounding the ven tral disk. Border of the mouth formed by a prominent membranous tube.
Genus 5. ENCRI NUS. Body supported on a jointed stem. (With one ex ception the species are all fossil.) Order I I. ECIIIXIDA.
Body globular or ovoid, without rays ; skin containing a calcareous shell ; anus distinct.
a. Regularia. Mouth and anus diametri cally opposite in the centre of the ventral and dorsal surface respectively.
Genus 1. ECM NUS. (/igs. 33 vol. i. 10-19.) Genus 2. CIDARITES.
b. illesostoma. Mouth in the centre, anus eccentric.
Genus !tows of feet extending Anus on