Body sacciform, without branchial openings, oral apertures situated at the inferior extremity of the longitudinal fissure in the mantle, and provided with a kind of maxillary apparatus; above or behind the mouth are annulate or horny filaments representing caudal fins or feet, upon the basal joints of which is a branchial filament. Here belong the Balani and Lepades—Fuss-kracken.
These animals are likewise sessile, at least when full grown, and are surrounded by shell-plates, which remind us of the Echini or Sea-Urchins, whose antetypes they are; this resemblance is particularly distinct in the Balani, which have similar odontoid valves upon the aperture or mouth of the shell. These animals also undergo a metamorphosis, since in the early periods of their existence they swim about like small Crustacea, and later on become fixed or sedentary, and surrounded by the plates of shell.
The Lepades have the ordinary shells of Mollusca, but each of the two valves consists of two pieces, between which an odd one is interposed down the back.
These five shell-pieces become in the Balani a regular set of teeth, which are adherent within the cylindrical shell, by which the posterior part of the body, or the peduncular and elongated mantle, is surrounded. (Vid. Oken's 'Allgemeine Naturgeschichte,' V, 1835, 509.)
They bear a resemblance to the Crustacea, not simply in the annulate horny feet, but also in the double and ganglionic nervous chord lying along the abdomen; only they are androgynous, which occurs in no Crustacean.
Order 2. Conchozooid Kracken—Kopfkracken.
Tentacula upon the head or fins upon the body. They repeat the Conchozoa or Shell-animals.
Fam. 4. Mussel-Kracken—Brachiopoda.
The body is surrounded by a mantle open above, and by two shells; on the sides of the mouth there are two arms.
These animals look exactly like Bivalve Mollusca; they are firmly adherent to rocks, being frequently supported upon a hollow pedicle, which is a prolongation of the mantle. Branchiæ and sexual parts but little known; species probably androgynous—Armkracken.