CIRRHOP'ODA, or CIRRIP'EDA (Gr. or Lat. eirrhns-footed), the animals which formed the genus lepas of Linnmus, ranked by him among the multivalve testacea, and by sub sequent naturalists very generally regarded as an order of mollusks, until, in conse quence of recent discoveries, a place has been assigned them among the articulate, either as a distinct class of that great division of the animal kingdom, or as a sub-class of erus tacea. Barnacles (q.v.) and balani or acorn-shells (see BALANUS) are the most familiar examples of C.; but many species are now known, all exhibiting much general similar ity to these, all marine, and all in their mature state permanently attached to objects of various kinds, as rocks, sea-weeds, shells, etc. Some are found imbedded in corals. others in the thick skin of whales, some in the flesh of sharks. They are distributed over the whole world; the species, however, are not numerous anywhere; those species which adhere to fixed bodies are in general much more limited in their geographic range than those which attach themselves to floating objects or to vertebrate animals. They are generally divided into two orders. pedunculated and sessile, those of the former order being supported on a flexible stalk, which is wanting in the latter. Barnacles are pedun culated C., and balani are sessile.
The resemblance of C. to mollusks consists chiefly in their external appearance. In the more important parts of their organization, however, the C. resemble crustaceans rather than mollusks. The gills, when these exist, occupy the same relative position as in crustaceans; but the aeration of the blood is supposed to be also effected in the eirrhi, as the limbs or organs have been generally called, of which there are six pair on each side, and which may be described as long tapering arms, each composed of many joints and ci2kted or fringed with stiff hairs. The eirrki nearest the mouth are shortest, and all of them together form a sort of net for the capture of minute animals, being inces santly thrown out by the cirrhopod from a lateral opening of its sac, and drawn in again in such a manlier as to convey any prey which they may have caught to the mouth.
Almost all the C. are hermaphrodite; but in a few genera the sexes are distinct, and these exhibit an anomaly of a very remarkable kind, the males Tieing not only very small in comparison with,the females, and more short-lived, but, in their mature state, parasitic on the females, or attached to them as they are to other objects; whilst in some the still more remarkable aileataly appears of what have been called complemental males, attached in this way to hermaphrodites. The eggs of C. are hatched before being finally set free from the body of the parent. The young possess the power of locomotion, swimming freely in the water, and are furnished with eyes, which disappear after they have per manently fixed themselves, by instinctive choice, in situations adapted to their kind. They have also shells, quite different from those of their mature state. The shelly cov erings of the C. are all formed according to a certain type, but with many variations, and they differ extremely in the number of pieces or valves of which they consist, some, as the common barnacles, having only five valves, and others having additional small pieces arranged in whorls, and exceeding 100 in number. In most of the C., the shelly cover ing is very complete; in some, it is almost rudimentary.
The most important discoveries concerning the structure and metamorphoses of the C., determining their place in the animal kingdom, were made by Mr. J. V. Thompson. For the most extended examination of species, and for an admirable monograph, pub lished by the Ray society, the scientific world is indebted to Mr. Darwin.