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Family Neritidae

SHELL solid, imperforate, top-shaped to patelliform; spire flattened; interior partitions absorbed; body whorl very large; muscle scar horse-shoe-shaped, seen in aperture; columellar region broad; lip simple or toothed; operculum calcareous, spiral or not, with prominent teeth on inner face, one of which locks behind the columellar lip. Snout short; radula long, well developed; tentacles long; eyes on stalks; gill single, on left side, triangular, free; mantle edges without cirrhi. A large family of littoral forms, most of which belong to tropical and subtropical oceans. They are greedy vegetable feeders, living on seaweeds. It is said that they are nocturnal in habits, ranging and feeding only at night. They are found near low water on rocks.

Genus NERITA, Linn.

Shell thick, smooth or spirally ridged and grooved, porcellanous, usually with horny epidermis; outer lip thick, columellar lip flattened, straight, toothed at margin. Animal with festooned mantle border. Feeds on algae by night. A gregarious, littoral genus, in warm oceans, including two hundred living and sixty fossil species.

The Bleeding Tooth (N. peleronta, Linn.) is found on the beaches of Southern Florida. It is well known among the coast dwellers. The broad columella bears two teeth, one or both of which are stained with a yellowish, bloody patch. The operculum is shelly and ear-shaped, and shuts more strongly because of a hinge formed by its hook locking behind one of the columellar teeth. The shell thickens greatly just back of the lip. Parallel ridges extend from spire to lip, crossed by fine striae.

The "bleeding tooth" is about 1 1/2 inches long; zigzag bands of purple, red and black on a white ground make it a handsome shell. There is great variation of pattern and colouring within the species. The mollusk is a rapacious feeder upon seaweeds. It is notable for the length of its rasping tongue.

N. versicolor, Gmel., is gay with streaks and squares of red and black, alternating with the whitish ground colour. Numerous strong rounded ribs follow the spiral and are crossed by zigzag markings. The species is smaller than the bleeding tooth and may be recognised by the four teeth on the convex lip of the columella. It is a West Indian species that ventures into Southern Florida.

The Tessellated Nerite (N. tessellata, Gmel.) has a checkered dark and light surface like a chess board, or in less regular arrangement, resembles the pattern shown in a snake's skin. Inside the aperture the outer lip is toothed, and small teeth are borne on the columellar lip. This solid, humped species is about an inch long. It occurs on the southeast coast of Florida, frequenting coral reefs and rocky beaches.

The three species described above are the only North American representatives of the genus.

Genus NERITINA, Lam. (NERITELLA, Humph.)

Shells thin, globose, with short spire, usually smooth; columellar lip broad, with fine marginal teeth, or smooth; outer lip sharp, not toothed within.

This genus includes about two hundred species. They live in rivers, except a few marine and brackish water species, and some which are amphibious, clinging to roots of trees on river margins. A few are terrestrial but live among the tree foliage overhanging the water. Most of them are tropical or sub-tropical in distribution.

The shells look like dainty, polished replicas of the Floridian "bleeding tooth." The animal within differs in no important particular from those of the more sturdy genus, Nerita. As with other tropical shells, there is much beauty of colour and pattern exhibited in this large group. Many forms are ornamented with spines.

The European Nerite (N. fluviatilis, Linn.) inhabits the gravelly bottoms of clear rivers; it extends over a very large area, and has many varities, some of which live in brackish water, and a few in salt water. The shell is transverse, the last whorl much swollen, white or decorated in a great variety of colours and designs. The largest are about 1/2 inch in diameter.

This mollusk lays its globular egg capsules on the shell of another individual. Each capsule contains fifty or sixty eggs. But only one of these develops. The remaining eggs serve to nourish the one growing offspring the capsule contains. We are strongly reminded of the "Yarn of the Nancy Bell." It would seem an unnecessary expense to feed a favoured individual on his own brothers and sisters because he happened to be the first to hatch, and so had them at a disadvantage.

N. reclivata, Say, is an olive or light brown shell, marked with fine zigzag lines of black, and about 2/3 inch in diameter. It is found in inland rivers of Florida. N. viridis, Linn., is a small bright green marine species. It is rarely found on Florida and Texas coasts.