CHITON, the name 1 given to fairly common littoral animals of rather small size which belong to the phylum Mollusca, and, in the possession of a radula in the buccal cavity, resemble more especially the Gastropoda.
Teeth of radula beam-like, and at most three marginal teeth on each side.
The radula when present comprises several transverse rows of teeth, and each transverse row may have several teeth (polystichous), two teeth (distichous), or one tooth (monostichous).
The labial commissure gives off a subradular commissure which also bears two ganglia, these being in close relation to a special sense-organ called the subradular organ, an epithelial projection with nerve-endings, lying in front of the radula and probably gustatory in function.
Ancistromesus, radula with median central tooth.
Hermaphrodite; head with appendage on right side; radula without central tooth.
Shell external, spiral, generally ornamented with ribs; borders of aperture thin and not reflected; radula with square teeth; genital ducts without accessory organs.
The radula consists of a chitinous band bearing teeth, secreted by a ventral caecum of the pharnyx and moved by an apparatus of cartilage and muscles.
Cephalic shield ending posteriorly in a median point; shell internal, largely membranous; no radula or stomachal plates.
Elongated, cylindrical, rounded at both ends; thick cuticle with acicular spicules; radula polystichous or wanting.