SYSTEMATIC BIOLOGY					KINGDOM ANIMALIA
HOME	SYLLABUS	WEEKLY ASSIGNMENTS	J. SYSTEMATIC BIOLOGY	TAXA OF LIFE
PHYLUM CHOANOFLAGELLATA

INTRODUCTION 

Choanoflagellata (ko-a-no fla-ge-LA-ta) is derived from a combination of Greek and Latin roots meaning funnel flagellates [funnel -choni (χωνί); and whip -flagellum).  The reference is to the funnel-like collar that surrounds the flagellum.

The choanoflagellates are free-living aquatic organisms (freshwater to marine) that range from unicellular to colonial species and resemble choanocytes, the flagellated collar cells of sponges (see A-D above).  The collar is made of microvilli that surround the single flagellum and serves as a filter for catching particles caught in the vortex created by the flagellum.  The individual cells or small colonies often are attached to a substrate by a stalk (B) or they can be free-floating (C).

SYNOPTIC DESCRIPTION OF THE CHOANOFLAGELLATA

SYSTEMATICS OF THE CHOANOFLAGELLATA

Until recently the choanoflagellates were considered to be part of the zooflagellates (Margulis and Schwartz 1988, 1998; and Buck 1990).   However, the choanoflagellates do not fit within that group very well, which prompted Sleigh et al. (1984) to raise the choanoflagellates to phylum-level status.  Taylor (1976), Lee (1980) and Sze (1986) tried to solve the same problem by associating the choanoflagellates with the chrysophytes.  However, details of the choanoflagellate cells are remarkably similar to those of the sponges.  Molecular data support that contention (Tudge 2000; Nielsen 1995).  Brusca and Brusca (2003) indicate that because the choanoflagellates seem to lack affinities elsewhere, they may be highly reduced sponges.  Molecular evidence also confirms their animal association (Wainright et al. 1993; Cavalier-Smith et al. 1996).  Adl et al. (2005) presented the choanoflagellates, a group that they called Choanomonada, as a rank equal to all of the Metazoa, Fungi, and nuclearid amoebae. Here, I consider them to occupy the animal subkingdom Choanozoa.  Please consult The Major Clades of the Animal Kingdom for some views on the relationships of the choanoflagellates with the other phyla of the animal kingdom.

The group has been divided according to the nature of the lorica that surrounds the cells.  Lee et al. (1985) separated the taxa into two families according to the types of loricas: cells naked or with a cellulosic theca and another group with a lorica constructed of silicaceous strips.  Cavalier-Smith and Chao (1997b) divided them into two groups according to the presence or absence of a lorica (theca).  The system presented here divides them into three groups and follows the divisions, but not the ranks, given by Adl et al. (2005).

HIERARCHICAL CLASSIFICATION OF THE CHOANOFLAGELLATA

This page is maintained by Jack R. Holt.  Last modified: 03/10/08