The Nut Shells - Family Nuculidae

THE NUT SHELLS - FAMILY NUCULIDAE. Shell bivalve, three-cornered or oval, small, pearly inside, hinge formed of small, comb-like teeth, interrupted by a central pit for the ligament.

Genus NUCULA, Lam.

Shell

with beaks turned toward the short posterior side; epidermis alive; hinge teeth sharp, comb-like; foot large, fissured, expanding into a fringed disk at tip; gills small, plume-like. About fifty species of small burrowing mollusks, chiefly in cold seas.

The Thin Nut Shell (N. tenuis, Montagu) is about as big as a grain of corn. Its smooth thin shells are protected by a bright green epidermis. This plain little shell is found north ward from Maine and along all coasts of northern Europe.

N. proxima,

Say, is a trifle larger, with an olive skin protect ing the finely cancellated surface, and crinkled margins. This is the common little nut shell of the Atlantic coast to North Carolina. It occurs also in western Florida.

A few other species are found on our colder coasts.

The Camp Nut Shell (N. castrensis Hds.) is a triangular brown shell, with sculptured markings, like an array of tents, on the surfaces. Inside it is pearly. The valves are no larger than half of a navy bean.

Habitat.— Deep water, California to Alaska.

Genus LEDA, Schum.

Shell

oblong, produced into an angle behind, usually rounded in front; margins not scalloped; hinge teeth as in Nucula; ani mal has two unequal siphon tubes, partly joined; mantle margins forming a third siphon in front; gills narrow, plume-like About eighty species, widely distributed in cold seas.

381 The Nut Shells The Finely-grooved Leda (L. tenuisulcata, Couth.) is drawn out, narrowed, and sharply keeled behind the umbones; it has a broad, rounded front. The surface is concentrically cut with fine lines, obscured in life by a thin, green epidermis. Length, inch.

Habitat.— New England northward, The Hooked Leda (L. bamata, Cpr.) a small flat shell, with its narrow posterior portion curved upward, is a deep sea form taken with a dredge near Santa Catalina Island. Its grooved sides are chestnut brown. Length, I inch.

T.

taphria, Dall, short-snouted, grooved and thick like a bean, t inch long, is found in San Pedro Bay.

Genus YOLDIA, March Shell thin, equivalve, polished outside, pearly within; dor sal line ends in angle behind; front rounded; valves flat; mol lusks active; usually found in shallows of river mouths or lee shores.

Cooper's Yoldia (Y.

Cooperi, Gabb) is a thin, close-ridged shell, with the hinge pointing backward and the sharp tip of the "tail" of the shell pointing upward. The comb-like hinge line

bears about twelve teeth in front and forty or more behind the beaks. The ribs are concentric. This deep water species occurs off the coast of California, and attains a length of two or three inches.

Y. Montereyensis, Dall, a

thin species with green epider mis and about twenty hinge teeth on each valve, is dredged from mud at the depth of half a mile in Monterey Bay. Length, i I inches.

The File Yoldia ( Y. limatula, Say) has a veritable file on the hinge line of each valve. The inconspicuous beaks are cen tral; the valve rounds in front, narrows behind, ending in a sharp angle at the dorsal line. A glazed green epidermis covers the smooth surface.

The slender united siphon is thrust up into clear water from the mollusk's normal station just below the surface of the mud. The foot is extremely broad and highly developed as a bur rowing organ. The thick, wedge-shaped extremity is thrust out obliquely at the front ventral margin, and when fully ex 382 The Nut Shells tended, dilated itself into two lateral flaps. Using this expanded disk as an anchor, the mollusk pulls the shell down toward it. Now the flaps close, forming a wedge-like cutting edge by which the mud is penetrated still deeper, and again the flaps dilate, and the shell is drawn down. In a second of time the Yoldia burrows several inches. Cormorants and flounders are its chief enemies. When out of its element the danger is greatest. On the sand Yoldia often leaps at surprising angles in a frantic at tempt to get back to the mud covert. Length, t to 3 inches.

Habitat.— New England to Cape Hatteras, Norway, Pacific coast.

The Broad Yoldia (Y. thraciaformis, Storer) shaped like the blade of an axe, has a diagonal crease from the pointed beak to the ventral angle of the posterior margin of the shell. The surface is dark olive green. Length, 2i inches. Height, t / inches.

Habitat.— New England coast.

Y. sapotilla, Gld., is like a half-grown limatula in outline, though narrowed less behind. The fragile valves are trans lucent, and coated with a glossy green epidermis. The lining is pearly white, with a triangular cartilage cavity, and nearly twenty sharp teeth on each side. Length, scarcely 1 inch.

Habitat.— Long Island northward, Alaska.

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