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A phylum of colonial, more-or-less sessile animals which form branching, encrusting or gelatinous structures made up of microscopic zooids. Each zooid is encased in a cuticular or gelatinous covering (zooecium) secreted by the body wall, and extends a circular crown of tentacles (lophophore) into the water to catch food. When disturbed, the tentacles are retracted and the body is drawn down into the zooecium.
Bryozoans occur in inland waters at the edges of clear lakes, in swamps and the backwaters of streams. Colonies may or may not be fully immobile. Some species can creep slowly on the vegetation or on rocky or sandy substrates.
The phylum is divided into two classes, Entoprocta (Code IO999999) and Ectoprocta (Code IM999999) , according to whether the anus is situated inside or outside the ring of tentacles. Entoprocta are almost entirely marine, with a single, widespread freshwater genus, Urnatella , not yet recorded from Australia. Ectoprocta is divided into subclasses Gymnolaemata and Phylactolaemata . One family of the former and three of the latter are recorded. A second family of Gymnolaemata is described from New Zealand.
Identification to Bryozoa can be based on the mat-like or moss-like colonial growth pattern in conjunction with the structure of the zooids. Bryozoa are most likely to be mistaken for lower plants (Bryophytes, etc.) or for Cnidaria (hydroid colonies). Plants have an entirely different internal structure. Hydroids have stinging cells (nematocysts) in the tentacles and a blind gut, and freshwater hydroids have many fewer tentacles than freshwater bryozoans.
Identification to family level can be based on external morphology and the growth form of the colony.
Tentacular structure (lophophore) circular, anus inside the ring of tentacles. Single freshwater genus Urnatella.
Chains or upright bunches of zooids with new branches arising from the base of an existing zooid. There is one Australian species, the cosmopolitan, brackish-water species Victoriella pavida .
2 Paludicellidae (New Zealand)
Branch-like colonies in which each zooid arises as a distal bud on the zooid proximal to it. New branches begin as lateral buds, often paired, so that the branching pattern generally is cruciform. Monotypic family for NZ endemic Paludicella articulata .
Lophophore horseshoe-shaped or clearly elliptical:
The colony sparingly and dichotomously branched, zooids distinct and circular, Lophopore more or less elliptic with 20-30 tentacles.
Branches antler-like or massed, zooids distinct and bilaterally symmetric, lophopore horseshoe-shaped with 20-80 tentacles.
Characterised by a gelatinous outer body covering. Branching pattern radial, each lophopore containing upward of 100 tentacles.
Williams, W.D. (1980) Australian Freshwater Life: The Invertebrates of Australian Inland Waters. The Macmillan Company of Australia, Melbourne.