Vorticella

Vorticella 

a genus of protozoans of the subclass Peritricha. More than 100 species are widely distributed in salt and fresh waters. Unlike other Peritricha, vorticellae are sessile, attaching themselves to a substrate by means of a nonbranching contractile stalk. The bell-shaped body lacks cilia. On the wide anterior end (adoral zone) is a double row of cilia that usually coalesce into membranelles involuted to the left (in contrast to protozoans of the subclass Spirotricha, whose membranelles curl to the right). The circumoral spiral leads to an oral opening. Vorticellae feed on small organic particles suspended in the water (for example, bacteria and detritus). In asexual reproduction, free-swimming zoospores equipped with a crown of cilia are formed as a result of division. They subsequently acquire a stalk and attach themselves to a substrate. The sexual process is a form of anisogamous conjugation, that is, the fusion of immotile macroconjugants and motile microconjugants. Some vorticellae are ectoparasites of fish.

IU. I. POLIANSKII