The Heart Cockle burrows in sand by means of its foot, going down just far enough to bury the whole of its shell, and always leaving its siphons exposed at the surface. It inhabits deep water, and is not likely to be obtained without the use of the dredge or trawl.
Fig. 144.—Cyprinidæ
1. Cyprina islandica. 2. Teeth of Cyprina. 3. Astarte compressa. 4. Circe minima. 5. Isocardia cor
The molluscs of the family Lucinidæ are found principally in tropical and sub-tropical seas, ranging from the shore to a very great depth, but a few are moderately common in our own waters. They are closely allied to the Cyprinidæ, but the shell is round rather than oval, and is obliquely grooved inside. The mantle lobes of the animal are not united on the ventral side, but at the posterior end they are continuous, except where they form one or two siphonal openings. The foot is long and of almost the same thickness throughout when extended; and the gills, numbering either one or two on each side, are large and thick. In all the members of this family, as in the last, the pallial line of the shell is simple. None of the shells are really common objects of our shores, since the animals inhabit deep water, some of them moving about freely on the bottom, while others moor themselves by means of a byssus.
We shall take only one example of the family—Galeomma Turtoni—the generic name of which means ‘weasel eye.’ This pretty little mollusc may be found on our southern coasts, where it often moors itself to the rocks or weeds by means of its silken byssus; or, having broken itself away from its temporary place of rest, creeps freely on the bottom by a long, flattened foot, applied closely to the surface over which it travels, and used much in the same way as the broad foot of a snail or whelk, its valves being all the time spread out nearly in the same plane.
Fig. 145.—Galeomma Turtoni