cirrus

A structure formed from a cluster or tuft of fused cilia, constituting one of the sensory or locomotor organs of certain ciliate protozoa. [L. a curl]

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cir·rus 'sir-əs n, pl cir·ri 'si(ə)r-.ī a slender usu. flexible animal appendage: as

a) a fused group of cilia functioning like a limb on some protozoans

b) the male copulatory organ of some worms

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cir·rus (sərґəs) pl. cirґri [L. “curl”] 1. any of various slender, usually flexible, appendages, such as one of the organelles used for locomotion by certain peritrichous ciliate protozoa; an eversible penis seen in flatworms; a fingerlike projection of a polychete parapodium; a branch of the thoracic leg of a barnacle; a lateral appendage on the stalk or aboral base of a crinoid; or one of the short projections around the mouth of a cephalochordate that together form a sieve to prevent large particles from entering the mouth. 2. a coarse hair on an animal, longer than most body hair but less coarse than a tactile hair or a vibrissa.