THE LIMPETS. TENT SHELLS - FAMILY ACMIEIDIE. Shell bowl-shaped, conical, with the apex a little in front of the middle, not spiral at any stage of development; with distinct internal border of the aperture; lining never iridescent; a free branchial plume at left above neck; radula lacks middle teeth. Mostly marine mollusks living on seaweed and rocks near shore.
Genus ACMIEA, Eschs.
The structure of a limpet may be made out with little trouble, for an animal that lives in such a shell cannot be very secretive as to the arrangements of its "in'ards." Slip a knife blade under the shell and it rolls off the rock into your harid. The branchial plume, extended at the left side of the neck when the limpet travels, is drawn in, but not concealed. The central, muscular disk is the foot, which has very remarkable tenacity when affixed to a rock face. In front the short head with its mouth and pair of tentacles appears; encircling all is the mantle border, lining the shell. From the mouth of a dead specimen draw the toothed radula, and examine the series of teeth under a good magnifier. This is the organ which' rasps the algae from the rocks.
What a safe shelter is the arching roof under which this mol lusk lives ! Yet to breathe, the shell must be slightly lifted. This gives watchful and hungry crabs and sea birds their only chance to catch limpets unawares. They are quick to save themselves when warned. But many pay for their inattention with their lives.
Should the strongest arm endeavour The limpet from its rock to sever, 'T is seen its loved support to clasp With such tenacity of grasp We wonder that such strength should dwell In such a small and simple shell.—Wordsworth.
The Limpet (A. testudinalis, Mull.), common on the Maine and Alaskan coasts, reaches } inches in length, 231 The Limpets. Tent Shells but in the British Isles it is smaller. Brown and green stripes radiate from the apex, crossing concentric circles of white and black on the gray ground in a more or less irregularly tesse lated pattern. The lines of growth are rather strong, and the
surface is finely sculptured with stria that cross each other. Within the aperture there is a brown and white tesselated border, then a white lining with a large owl-shaped patch of brown, the muscle scar, under the apex.
This sluggish mollusk wanders forth to feed on the soft tissues of alga. It returns to its own place on the under side of a rock after each excursion.
Var. alveus, Conr., is so thin that the checkered pattern is seen through the wall. The sides are compressed to fit the shell to the stems of seaweeds on which it lives. The elevated peak sometimes forms a forward-pointing hook.
These, like the typical tortoise-shells, are found in cold waters on both Atlantic and Pacific coasts of North America, along with forms that intergrade between them.
Habitat.— West Florida, Bahamas.
The west coast of the United States is particularly rich in species and varieties of this genus. I will not describe all of them, but select the most common and distinctive.
The Plate Limpet (A. patina, Eschs.), modified forms of which show it to be closely related to A. testudinalis, is the most characteristic limpet of the west coast. The shell is flattened, the blunt apex near the middle; the back is gray, finely tesse lated with black. The flesh is white. Length, 2 inches.
Habitat.— Aleutian Islands to San Diego, Cal.
The Rough Limpet (A. scabra, Rye.) is sculptured with close, radiating, scaly ridges diversified regularlyby ribs of greater size and elevation. Yellow with faint brown markings is the usual colouring. The apex is low, the slopes convex. The flesh is black.