CIRRHOPODA ; Cirripedia ; Cirripeds ; (x.c?gO5 and frac, cirrus and pes, from the curl like form which the coiled feet or arms present. Fr. Cirripedes. Ger. Rankenfuesser.) A class of .invertebrate animals, composed chiefly of the barnacles and acorn-shells. They are re lated in some points of structure with the annu lated or diploneurose animals, particularly with Crustacea ; in other points they resemble Ace phala (Conchifera). All are marine and fixed. The soft parts are, for the most part, encased in a multivalve shell. The body is somewhat conical in form, tumid, and bent inwards at the oral extremity, tapering towards the oppo site extremity, where it terminates in a long pointed tube. Placed along the abdominal surface, there are two rows of fleshy lobes, (six on either side,) each having two long horny processes, jointed and ciliated*. In some species, these constitute the chief bulk of the whole animal. The head is indistinctly de fined, and has neither eyes nor 'tentacles; mouth with lips, and three pairs of horny jaws ; anus at the base of the tubular process. Respiration is effected by branchim, which, in some species, are filamentary, in others foli ated. Mantle membranous, sacculated; pro vided with a slit-like opening for the passage of the arms, &c. Between each two pairs of arms, the abdominal surface is marked by six slight depressions, which may be regarded as an approach towards complete articulation.
The animals thus characterized have had dif ferent places assigned to them in the various systematic arrangements of modern zoologists. Cuvier formed of them the sixth and last class of his Mollusca. Lamarck was at one period inclined to place them amongst the Crustacea, but latterly he constituted for them a distinct class, and placed it between Annelida -and Conchifera ; still, hcmever, regarding them as more closely allied to Crustacea than to any other class ; " for," as he remarked, " they have the nervous system of Crustacea, they have jaws analogous to those of the animals of that class, and their tentacle-like arms resemble the antennT of the lobsters." Bur, meister also places them amongst the Crus tacea. De Blainville arranges them, under the name of Nernatopoda, as a class of his subtype of the Mollusca — Mollusc-articulata ; the other class of the subtype being formed of the Chitons (Polyplakiphora). He reg,ards them as Crustaceous Mollusca, but admits that they seem to form a transition group uniting the Crustacea with the Annelida. M.
St. Ange,* however, would rather class them with the Annelida, on account of the closer resemblance which the arrangement of their nervous system bears to that of these animals. Professor Wagner does not doubt that they are really articulated animals, but he would rather place them in a distinct class between the Mollusca and Articulata. Setting aside their nervous system, M. Serres sees, in the other parts of their structure, points enough to in duce him to armnge them with the Mollusca. The same views are entertained by Wiegmann, Goldfuss, and others. Dr. Leach regarded them as truly annulose animals. Dr. Grant (who calls them " entomoid animals enclosed in shells") places them amongst the Articulata, or diploneurose animals, between Itotifera and Annelida, making of them a distinct class, but admitting their great resemblance in many points to the entomostracous Crustacea. Mr. J. V. Thompson (whose admirable researches on the development of the Cirripeds have thrown a new interest around them) holds it as proved by his observations that the Cirripeds do not constitute a distinct class; but that they are naturally and closely connected, on the one hand, with the Decapod Crustacea, through the Balanids, and, on the other, with the Entomostraca, through the Lepads ; further, that they have no relation with the Testacea.
All the known Cirripeds inay be naturally grouped into two families, one pedunculated, the other sessile. The former includes all the barnacles, properly so called the latter, the acorn-shells. The barnacle fa'mily have had the name of Campylosomata applied to them by Dr. Leach, who calls the other family Acamtosomata : but we shall use De Blain ville's synonyms of Lepadicea and Balanidea. The followin,,o- are • the names of the genera generally used at present:— External coverings and organs of support.— There are three principal modifications of the tegumentary organs in this class. The first is that seen in Anatifa, in which it assumes the form of calcareous plates, united by horny ligament, and attached to a cartilaginous pe duncle. The second form is that common to all the Balanids—a calcareous cone, composed of separable pieces, sessile, and provided with an opercule of shelly plates. The third form is a general cartilaginous covering, sometimes strengthened by small calcareous plates.