The radula has 160 rows of teeth with twelve teeth in each row.
Teeth of radula beam-like, and at most three marginal teeth on each side.
Ancistromesus, radula with median central tooth.
Hermaphrodite; head with appendage on right side; radula without central tooth.
Radula with ver y numerous marginal teeth arranged like the rays of a fan.
In the radula there is a single central tooth or none.
The order is now divided into two sub-orders: the Taenioglossa, in which there are three teeth on each side of the median tooth of the radula, and the Stenoglossa, in which there is only one tooth on each side of the median tooth.
Radula with a median tooth and three teeth on each side of it.
The three following families have neither radula nor jaws, and are therefore called Aglossa.
Radula narrow with one lateral tooth on each side, and one median tooth or none.
Radula with a median tooth and a single FIG.
Shell solid, piriform, with thick folded columella; lateral teeth of radula bicuspidate.
Shell elongated, with long siphon; lateral teeth of radula multicuspidate.
Shell irregular; radula absent; foot and siphon short; sedentary animals, living in corals.
(Formula, x.l.x.) radula has a number of uniform teeth on each side of the median tooth in each transverse row.
Margins of foot not prominent; no radula; shell external, with inconspicuous spire.
Cephalic shield ending posteriorly in a median point; shell internal, largely membranous; no radula or stomachal plates.
Head broad, surrounded by a funnel-shaped velum or hood; no radula; dorsal appendages foliaceous.
Pharynx suctorial; no radula; branchial rosette on the dorsal surface, above the mantle-border.
No mandibles, and radula uniserial.
Have a twisted visceral nerve-loop, an operculum on the foot, a complex rhipidoglossate or taenio-glossate radula, and are of distinct sexes.
The Pulmonata have a straight visceral nerve-loop, usually no operculum even in the embryo, and a multidenticulate radula, the teeth being equi-formal; and they are hermaphrodite.
Radula with elongated and pointed teeth, like those of the Agnatha; a jaw present.
Shell external, smooth, heliciform or flattened; radula with pointed marginal teeth.
No shell; mantle covers the whole surface of the body; radula with squarish teeth.
Shell internal, or absent; mantle restricted to the anterior and middle part of the body; radula with squarish teeth.
Shell external, spiral, generally ornamented with ribs; borders of aperture thin and not reflected; radula with square teeth; genital ducts without accessory organs.
The latter were regarded as forming a distinct branch, equivalent in rank to the other three classes together, the latter all possessing the radula which is wanting in Lamellibranchs.
The characteristic organs of Mollusca are the mantle and shell, the foot, the ctenidia and the radula, of which all but the last are external.
The alimentary tube consists of three regions: firstly, the anterior buccal mass with the oesophagus, of ectodermic origin, and therefore bearing cuticular structures, namely the jaws and radula; secondly, the mid-gut, of endodermic origin and including the stomach and liver; and, thirdly, the hind-gut or intestine.
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.
Beneath the anterior parts of the radula where it emerges from the caecum are a pair of cartilages, and attached to these a number of special muscles by which the radula is moved backwards and forwards to act as a rasp. The secretion of the radula at the closed end of the caecum is continuous, so that it is constantly growing forward as fast as its exposed anterior portion is worn away by use, just as a fingernail is pushed forward by constant growth at its posterior end, and is worn away or has to be cut short from time to time at its outer end.
This has led to the loss of the radula, and is accompanied by the division of the shell into two valves.
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.
Hubrecht in 1881 of a typical molluscan radula and odontophore in a new genus Proneomenia, allied to Neomenia, showed that the whole group belonged to the Mollusca.
Each transverse row of teeth of the radula contains 17 teeth, one of which is median, while the second and the fifth on each side are enlarged.
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.
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).
It is a curious fact that in the original type Neomenia the radula is entirely absent, as it likewise is in several genera of Proneomeniidae.
Elongated, cylindrical, rounded at both ends; thick cuticle with acicular spicules; radula polystichous or wanting.
Short and truncated in front; thick cuticle, often without papillae; gills and 7 radula present.
On the floor of the pharynx or buccal mass is a rudimentary radula, which in many species consists of a single large tooth, bearing two small teeth or a row of teeth.
In other species the radula is more of the usual type consisting of several transverse rows of two or three teeth each.