Limpets
LIMPETS Genus CREPIDULA, Lam.
Shells oval, with a horizontal plate closing about one-half of the aperture. Apex lateral, spiral; head flat; foot short; very common shells on all American beaches.
The Arched Slipper Shell (C. fornicata, Linn.) is loved by children, it is useful in so many ways when seaside play houses are to be furnished. The boat shape appeals to the imag ination, with its broad bottom, its rounded stern and comfortable seat. Balanced on the table and on cupboard shelves these shells are the little housekeeper's joy in setting forth dolls' tea 148 The Slipper Shells. Cup-and-saucer Limpets parties. There is never any scarcity of dishes; the tide is always bringing in new ones.
Grown-up people, too, find a use for the empty shells. Fisher men at Greenport, Long Island, dredge up the accumulation of dead shells and sell them to oyster growers for "stool." This means that they are scattered over the rocky floor of new beds for the embryo oysters to settle upon. "Quarter-decks" is the trade name they go by. They are taken with the "jingle shells," which frequent the same banks, and are also excellent as oyster stool. In 1887 Greenport alone sold 130,000 bushels of the two shells to the oyster growers for $5,200, an average price of four cents per bushel.
English oyster beds are in some places replenished with "seed" from American growers. With these young oysters C. fornicata has been introduced. Conditions are favourable to growth, and the "crow oyster," as it is called, has become a nuis ance. The edible oyster, when overloaded with slippers, often three to six deep, is stunted and unsightly. The parasites rob the oysters of their food, and choke them besides. There seems to be no way of getting the better of the invader.
This species is the largest of its genus; the shells are from one to two inches long. The spiral apex is drawn down to one side of the posterior end of the shell. From it indistinct lines of pinkish brown, often broken into dots or broadened into streaks, paint the almost smooth surface. The polished interior is mottled with brown and violet in large patches. The par tition is white and thin.
The height of the shell arch is largely dependent upon the life of the mollusk. Some individuals are free, and have very concave shells, others affix themselves to stones, or to the shells of oysters and various other mollusks. These are modified in form by the surface to which they adhere. On a scallop shell the Crepidula will be ribbed. Sometimes slippers are found piled one upon another in tiers of six or more. This is especially common in northern waters. They feed upon seaweeds for the most part, but have been known to eat other mollusks.
It is known that some of these mollusks move, and perma nently change their positions. A certain specimen may spend a part of its life on a ribbed shell like an Arca or a Pecten, then move to a smooth shell or stone. The growth of the shell will 149 The Slipper Shells. Cup-and-saucer Limpets tell the story plainly. The horseshoe crab (Limulus) often carries a load of upward of one hundred slippers. Length, I to 2 inches.
Habitat.—Maine to Brazil.
The Flat Slipper Shell (C. plana, Say, C. unguifortnis, Lam.) is found flattened against the walls of apertures of dead shells. Growth proceeds, and the broadening shell of the slipper becomes concave on the back, parallel to the concavity of the body whorl within which it is attached. Examine the shells of Natica for slippers of this peculiar form.
The shell is usually white, the apex claw-like, as Lamarck's scientific name defines it. The pointed end is fitted with a tri angular shelf. The other end is broad like a spade. According to Professor Conklin, the female is fifteen times as large as the male. This species is small and frail. Length, I inch.
Habitat.—Maine to Florida.
C. aculeata,
Gmel., is common on Florida and California beaches. Smaller than the arched slipper, it resembles it in being marked with brown, and having a white "seat" in the end. The shell has radiating ribs which bear faint knobs.
This species has a remarkable world-wide distribution on warm beaches.
C. glauca
is a little hump-backed species that keeps company with the small hermit crabs which live in the dead shells of the dog whelk. It is an Atlantic coast form.
The Pacific coast has several slipper shells. C. aculeata and C. plana are there. C. adunca, Sby., with high apex strongly recurved, is about an inch long. It is brown with a white shelf inside. This is the most common western species.
The Wrinkled Slipper Shell (C. dorsata, Brod.) is nearly round in outline, and often bent so that the shelf is two-lobed resembling the twisted cup in some species of Calyptrwa. The thin, flat shell is brown and white, and about 4 inch long. It is common on California beaches.
The White Slipper (C. Lessonii, Brod.) is handsomest in the form that wears ruffles on its shell, along the lines of growth. It is distinguished by its whiteness, its flatness and by the delicacy of its shelf. There is much variability in this Californian species.