Choanoflagellida

(invertebrate zoology) An order of single-celled or colonial, colorless flagellates in the class Zoomastigophorea; distinguished by a thin protoplasmic collar at the anterior end.

An order of the class Zoomastigophorea, superclass Mastigophora, subphylum Sarcomastigophora, in the phylum Protozoa. They are principally small, single-celled or colonial, structurally simple, colorless flagellates distinguished by having the anterior end surrounded by a thin protoplasmic collar, within which is an ingestive area for particulate matter, for example, bacteria. A single flagellum arises from the center of this collar (see illustration). They are widespread in fresh and salt water and are common in inshore waters. See also Protozoa; Sarcomastigophora; Zoomastigophorea.

A linear colony of the choanoflagellate, Desmarella moniliformis.