THE HORSE MUSSELS Genus MODIOLA, Lam.
Shell cylindrically oblong, inflated in front, with beaks small, rounded, almost, but not quite terminal; epidermis often produced into a beard-like fringe ; byssus ample, fine. Animal as in Mytilus; flesh orange or red.
A widespread genus of seventy species, chiefly tropical, includes the nest-builders of the family. Some cling in masses, as Mytilus does. The coarseness of the flesh and its unfitness for human food are indicated by the name.
The Common Horse Mussel (M. Modiola, Linn.) is like the edible mussel in outline, but the shell is much swollen, and the beaks are not at the very end — a prolongation of the shell extends farther in front. The valves are thick, and the glossy brown epidermis wears a shaggy coat of hair, especially toward the ventral posterior area. The flesh is orange-coloured, the foot red. The mollusk harbours a little pea crab which is en tirely free from spines. Found in muddy gravel, from low water to eighty fathoms depth. Or they hide in rock crevices, where they are washed by the tide at high water. In mud the mollusk stands vertical, its nose buried, its siphons up in the water. In the region of Vancouver this "great horse mussel" grows to be nine inches long and four inches wide. On northern coasts of England it may attain an equal length, though the average is about five inches. This is the size we commonly see it.
Habitat.— Cape Hatteras northward, California to Alaska, northern Europe.
The Plaited Horse Mussel (M. plicatula, Lam.) is narrowly and triangularly oblong, gibbous, spreading and compressed behind, plaited finely in radiating lines, especially strong over 390 The Mussels and Rock-eaters the posterior area. The dark brown epidermis is tinged with yellow. Ligament long and strong. Lining silvery white.
This is one of the most common mussels on the muddy tide flats of our east coast. It has the clinging habits of Mytilus. Length, 2 to 4 inches.
Nova Scotia to Georgia.
The Tulip Modiola (M. tulipa, Lam.) is oblong like a small M. plicatula, but striped with alternating rays of yellow and chestnut. It is the gayest of our native mussels, and is naturally a southern species. Length, 2 to 3 inches.
Carolina to West Indies.
The Straight Horse Mussel (M. recta, Conr.) is long and narrow, with delicate, ventricose shell, shading from dark to lighter brown from the beaks outward, and becoming quite hairy toward the end. Length, 3 to 4 inches. Var. flabella, Gld., grows to greater size.
Vancouver to southern California.
Genus MODIOLARIA, Beck Shell oblong, with hinge at one end, ribbed radiately, but with a plain central area separating the ribbed portions ; foot strap-shaped, very extensible. This mussel lives in rock crevices, in empty shells, or buried in the tests of simple ascidians. When moved to change its quarters it is active, and uses the tip of its foot as a prehensile organ, grasping stems of seaweed and other objects to help itself along. When a new place is selected, at tachment is made by spinning a byssus.
The Black Modiolaria (M. nigra, Gray) changes its outer colour with age from purple or olive brown to black. Its out line is almost oval, the ribbed areas are crossed by concentric lines so as to form a fine network with knobs at the intersections. Length, 3 inches ; width, 2 inches.
Arctic seas to Cape Hatteras, Pacific coast, Europe.