CLASSIFICATION. Barnacles are classified upon the manner of life and the method of attach ment. The order Cirripedia is divided into five families, as follows: (1) Lepadida• having the head end elongated to form a flexible stalk.
(2) Balanidir. without a stalk. but having the body surrounded by a ring of calcareous plates.
(3) Alcippidce, without stalk, or ring of. plates, only three or four pairs of feet.
(4) Proteolepadidw, without stalk, plates, or feet.
(5) Kentrogonidre, without stalk, plates, feet, mouth, or digestive system.
The last three of these families are parasitic, and their reduced structure is directly traceable to their mode of life. The anatomy and natural history of barnacles can be most clearly stated by treating each family separately, though it may be said once for all that all barnacles are marine, except a single brackish-water species of &lianas.
The Lepadida. take their name from the Greek word Xercis, a limpet, probably with reference to their being attached forms. The head end is more or less elongated to form the stalk by which the animal is attached. This stalk is fleshy, but tough and flexible; its length] varies greatly, up to 10 or 12 inches. Within it are contained the cement gland, with its duct opening at the tip. and, near the base. the ovary, with oviduct open ing above in the mantle cavity. The oral portion of the head, the trunk, and the appendages are eontained within the mantle, which forms a lat erally flattened sac, opening by a slit-like aper ture at the upper or outer end, on the ventral side. The mantle is chitinons, hut contains, de posited in its wall, the plates of lime which com pose the shell. There are five of these plates, a median unpaired one (the ear inn) on the dorsal side, an anterior one on each side (senta), and a posterior one to each side (terga). There may also be small accessory plates on each side. The animal is so placed within the mantle that the mouth opens on the upper side of the attached end, the trunk curving backward and upward, and bearing the curious tendril-like feet on the ventral side. These feet are thus above the mouth, and in life project more or less freely from the opening of the shell; they are very flexible, and by their movements are continually bringing particles of food into the mantle cavity and down to the mouth. There is a liver or digestive gland connected with the stomach, but a large part of the trunk is occupied 1)3' the male reproductive organs. On the ventral side of the body is a strong muscle, by means of which the shell can be tightly closed. The nervous sys tem consists of a brain and a ventral cord; but sense-organs, other than those of touch. seem to be wanting in all adults. though eyes are present in the larvae. The Lepadicke are very widely dis tributed. but occur chiefly in the warmer seas.
They are popularly known as goose-barnacles or goose-mussels, the latter name referring to the superficial resemblance they have to the mollusks known as mussels (q.v.). Although this resem blance is very slight, barnacles were long classed as mollusks because of the presence of a shell. The number of species of goose-barnacles is not large; but. owing to their becoming attached to the bottoms of ships, they are transported from one side of the globe to the other, so that the same species sometimes occurs in the harbors of Europe, Asia, Africa, Australia, and both coasts of America. Naturally, those which attach them selves to rocks or other fixed bodies have a much more restricted range. None of the Lepadidie are of large size; the body is usually under an inch in length. though the stalk is sometimes ten times as long. The colors are generally incon spicuous--the stalk and mantle pale brown, the calcareous plates pearly blue. None of the Lepa didre have any economic value.
The Rolanielai take their name from the Greek word piXavos, an acorn, in reference to the shape of the shell. In Great Britain these barnacles are usually called 'aeorn-shells,' but the name is not in common use in the United states. The shell is much more fully developed than in the Lepadidie, and owing to this and the absence of a stalk, they differ superficially from that family to a marked degree. The mantle forms a truncated conical sac, attached by the base, and opening at the up per or posterior end. This opening can be closed by four plates which correspond to the senta and terga of the goose-barnacles. The mantle itself calcifies into six or more vertical plates. which are broadest at the base, and which can be more or less drawn together at the top, over the scuta and terga. The internal anatomy is very similar to that of the preceding family, but the ganglia of the ventral nerve-cord are fused into a single large ganglionic mass. The are even more widely distributed than the Lepadida,, and are more abundant in the colder oceans. They often incrust rocks, wharf-piles, and other sub merged timbers, and the bottoms of boats, and are frequently found on crabs, mollusks, and other marine animals. They are generally small, less than 2 inches in height; but the largest known barnacle is lialanus psittacus, which is sometimes 9 inches high and 4 inches in diame ter. This species is of additional interest from the fact that large quantities are gathered on the coast of Chile for food and export. Other species are also eaten, especially by the Chinese, and the Romans regarded some of the :Mediterranean forms as great delicacies. The flavor is said to be like that of other crustaceans. as shrimps, lob sters, etc. The shells of the are very hard, and when clean are almost pure white.