parrot-like beak presents a strong exception to the general softness of this animal; it is so hard, stout, and stony, and moved by such powerful muscles, that the strong shells of bivalves and univalves are not able to resist its force: even the hard and stony limpet is dragged from its attachment, and crushed to pieces in these powerful mandibles.
1 ↑ Edinb. New Phil. Journ. XVII. 319.
2 ↑ Whaling Voyage round the Globe.
3 ↑ Penny Cyclop. art. Sepiadæ.
CLASS II. PTEROPODA.
(Fin-footed Mollusks.)
This is a very small Class, comprising a few species of curious structure. They are all of diminutive size, and all swim in the open ocean, rarely approaching the shore, except when washed thither by accident. They are all characterised by having a membranous expansion, resembling a large fin, on each side of the head. By means of these organs, the little Pteropod rows itself about in the open sea perpetually; being unfurnished with any means of crawling, or of affixing itself to any solid body. Some of these animals, as the genera Hyalæa (a) and Cleodora (b), for example, have the body enclosed in a shell of elegant form, and of
GLASS SHELLS.
a texture resembling the thinnest glass, for delicacy and transparency. The Cleodora pyramidata, one of the species of the latter genus, is of extreme delicacy and beauty. The shell is glassy and colourless; very fragile; nearly in the form of a triangular pyramid; with an aperture at its base, from which proceeds a long and slender glassy spine; and a similar spine projects from each side of the middle of the shell. The hinder part of the animal is globular and pellucid, and in the dark vividly luminous, presenting a singularly striking appearance, as it shines through its perfectly transparent lantern. Both of these are found floating in great numbers on the surface of the tropical sea.
Others are entirely destitute of a shelly covering, as is that little species which occurs in enormous profusion in the Arctic Seas, and which we now proceed to describe.
Genus Clio.
("Whale-food.")
These little creatures have an oblong membranous body, without a mantle; a head formed of two rounded lobes, each of which is furnished with three long tentacles, capable of being withdrawn into a fold of skin, or protruded at pleasure. The mouth, which is terminal, has two small fleshy lips; and two eyes, of elaborate structure, are placed at the back of the neck.
The species best known is that which is commonly called by our northern voyagers, Whale-food (Clio borealis). Though not more than an inch in length, it occurs in such countless millions as to form the principal part of the nourishment required by the most gigantic of living creatures. The Clio bears some slight resemblance to a butterfly just emerged from the chrysalis, before the wings are expanded. Near the head there is on each side a large fin or wing, by the motions of which it changes its place.
Thus, therefore, there will be three hundred and sixty thousand of these microscopic suckers upon the head of one Clio: an apparatus for prehension perhaps unequalled in the creation.
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