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Family Littorinidae

SHELL spiral, turbinate or globular, not pearly; aperture oval or circular, entire; lip simple; columella thickened, flattened; operculum horny, of few coils; snout wide, short; eyes on swellings at outer bases of the long tentacles; foot broad and square in front and behind, divided lengthwise; radula long and narrow. Reproduction by eggs hatched within or outside the body.

Genus LITTORINA, Fer.

Characters of the family. A large genus of 150 species, living on rocks between tide marks. Some live in brackish, some in fresh water. Some species are amphibious and can survive long periods of drought. Some live on aerial roots of mangrove trees, where they overhang the water and get the dash of its spray. The distribution of the genus is world-wide. It is rapidly spreading on American coasts.

Periwinkles furnish an important article of food to European markets, where they are bought by the poorer and middle classes. They are also an important bait for fish.

The Shore Periwinkle (L. littorea, Linn.) is a mollusk fitted by nature to survive in the struggle for existence. Abundant on all the shores of Northern Europe, it has colonised New England and is rapidly extending its range southward. Its solid shell and horny operculum make an impregnable fortress against foes without.

The name periwinkle, is an old one. It is supposed to be modified from "petty winkle," the small one, to distinguish it in the London markets from the large winkle, or whelk, Buccinum undatum. Both are staple foods in England. Thousands of tons of this dingy little mollusk are collected each year for the city trade by women and children on the rocky coasts of the British Isles, and sold from corner stalls or push carts in the streets. They are used as food in other European countries. The Portuguese of Provincetown and other points on Cape Cod gather them in quantities.

An immigrant from England, this species has come to our coasts via Iceland and Newfoundland. Its invasion has rapidly progressed southward past Cape Cod and Long Island to the New Jersey beaches. On the rocky coasts of Maine it is found in greatest abundance, covering the sides of huge boulders and wharf piers exposed by the outgoing tide, clinging to seaweeds and stems of marsh grass, or crawling in ditches, and tide pools.

The shells are brownish yellow to olive or gray, sometimes spirally banded with dark red and brown. Sometimes they are black. There is great variability of colouring. They are thick, with seven or eight whorls, ribbed spirally. There is no umbilicus; the lip is thin and black; the columella broad and white. The aperture is round; the operculum horny. The spire is sharp, but the shell has a squat shape, the base and height are each about 3/4 inch. The males are smaller than the females.

The periwinkle is a vegetarian, as are nearly all round-mouthed snails. Coiled inside the mouth is the radula or rasping tongue, about three times as long as the body (2 1/2 inches); it has six hundred rows of sharp, curved, tricuspid teeth, seven in each crescentic row. Here is the weapon for scraping off the algae which grows on rocks near shore. Knowing their feeding habits, the owners of oyster beds scatter periwinkles on their acreage to keep the hindering algae grazed close.

The gait of the periwinkle is slow and uneven, one side of the foot moving forward as the other holds fast: another good instance of a "snail's pace." A median line divides the foot lengthwise into two areas which act alternately in walking. A gland in the foot secretes copious slime. The eggs are laid in masses on seaweeds or rocks.

The Common Periwinkle (L. irrorata, Say) is a heavy, sharp-pointed conical shell, of a few finely ridged whorls. Numerous chestnut dots, in spiral lines, give a brownish colour to the exterior; the smooth columella is also brown. The lipis thick but bevelled suddenly to a thin edge and dotted with brown. This is the periwinkle of the Gulf of Mexico, which has gradually progressed northward for years, overlapping the range of the less robust L. littorea. We look for both species on rocks between tide marks, and in stagnant pools and marshes. They seem to avoid the dash of the surf, though they are built to resist harm from wave action. Length, 1 inch.

Habitat.--Florida to New York.

The Rough Winkle (L. rudis, Don) is at best scarcely half an inch in length, with rounded whorls separated by deep sutures. The female carries her eggs until they hatch, hence the last whorl is fully two-thirds of the whole shell and the round mouth is much larger than that of a male shell of equal size. This species is banded in neutral colours, from yellow to black. It can live out of water for a week. Marked specimens on the rocks were found not to have moved for over a month. The shells of the young brood render these periwinkles inedible. Their size, also, makes them hardly worth while. Length, 1/6 to 1/2 inch.