Body cylindrical, very plentifully supplied with muscles. Mouth and anus present, the former of these being surrounded by a dental wreath and ramified branchimorphous tentacula; branchiæ upon the intestine, and branchial aperture at the anal extremity. They correspond to the Physaliæ.
Their tegument is a perfect muscular tunic, consisting of several longitudinal bands, which pursue a downward course upon its internal surface; in other respects being transversely corrugated and full of papillæ, partly replete with hollow podoidal filaments, which by the injection of water into them are elongated; thus, they present a resemblance to the Acalephæ.
Fam. 8. Beroeal Worms, Echini.
Are at bottom Holothuriæ with ossified tegument, or Asteriadæ with shortened rays.
The Echini have an anus, pretty like that of the Holothuriæ, and also similar feet, which are protruded in a similar manner through apertures in the shell. The dental wreath surrounding the mouth is a complete bony framework, which has been called, on account of its form, "Laterna Aristotelis," and bears a considerable resemblance to the valves of the Balani, the antetypes in general of the Echini, just as these are of the Opossum Shrimps.
Fam. 9. Medusal Worms, Asteriadæ.
Body stelliform, consisting of bony rings; contains a free multilobular intestine with blood-vessels and branchiæ; several ovaria; it would appear that they are without male parts.
Here belong the Encrinites, Pentacrinites, and Asteriadæ proper. Around the mouth of the Encrinites and Pentacrinites stand long, ramified, and likewise articulated tentacula, which remind us of the arms of the Acalephæ and Cephalopoda.
Fundamentally too, in the Star-fishes, the disk only is the body proper, and the rays are the tentacula, which, being monstrously developed, surround the mouth; what have been called pedicles upon these, represent the suckers of the Sepiæ.
Eighth Class.