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In biology, a cirrus , plural ''cirri'', , (from the Latin ''cirrus'' meaning a ''curl-like tuft or fringe'') is a long, thin structure in an animal similar to a
In biology, a cirrus , plural ''cirri'', , (from the Latin ''cirrus'' meaning a ''curl-like tuft or fringe'') is a long, thin structure in an animal similar to a tentacle
In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...
but generally lacking the tentacle's strength, flexibility, thickness, and sensitivity.
In the sheep liver fluke, for example, the ''cirrus'' is the worm's muscular penis and when not in use is retained within a ''cirrus sac'' or ''pouch'' near the animal's head. The same structure exists in the various ''Taenia'' species of tapeworm. In the clam worms, however, the cirrus is the tentacular process or growth on each of the feet (''parpodia''), either the ''dorsal cirrus'' or the ''ventral cirrus'', and has nothing to do with reproduction.
Among the bristleworms, a cirrus is a tentacular growth near the head or notopodium containing sense organs and may be either dorsal, ventral, or lamellar. Among the ribbonworms, the ''caudal cirrus'' is a small thread-like growth at the posterior end of the worm. Among feather stars or barnacle
A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...
s, a cirrus is a long slender gripping or feeding appendage.
In sea lilies
Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which ar ...
, the cirri are the thin strands that line the animal's stalk. Among the tube blennies, a cirrus is a long growth extending from above the eye (a ''supraorbital cirrus'') or extending below the neck-region (a ''nuchal cirrus''). In a nautilus, each of the animal's tentacles is composed of a thin flexible cirrus and the corresponding hardened and protective cirrus sheath into which the cirri may be withdrawn.
References
{{Zoology Animal anatomy Annelid anatomy