Bryozoans are divided into three groups:
Freshwater bryozoans with no zooid polymorphism, no calcification; form
resistant overwintering structures known as statoblasts. No fossil
record except for a few statoblasts from Quaternary sediments.
Marine bryozoans with tubular zooids with calcified walls. Lophophore is
protruded by action of annular muscles. Includes
- Trepostomata: Colonies generally robust; dendroid, encrusting,
or massive. (Ordovician - Triassic)
- Cystoporata: Colonies robust or delicate. (Ordovician - Triassic)
- Cryptostomata: Colonies typically delicate; foliate or dendroid.
(Ordovician - Permian)
- Fenestrata: Colonies typically delicate; reticulate (net-like)
(Ordovician - Triassic)
- Tubuliporata, or Cyclostomata (Ordovician - Recent)
Mostly marine bryozoans with cylindrical or flattened zooids.
Lophophore is protruded by action of muscles pulling on frontal wall.
Includes the majority of living bryozoan species, traditionally classified
into two sub-groups:
- Ctenostomata: Uncalcified forms, including several that bore
into calcareous substrates. Opercula rare. Eggs brooded in body cavity.
(Ordovician - Recent; almost all fossils are traces of boring forms.)
- Cheilostomata: Calcified forms, usually
with opercula. Eggs usually brooded in
ovicells. (Jurassic - Recent; includes majority of living forms.)
McKinney, F.K. and Jackson, J.B.C. 1989. Bryozoan
Evolution. University of Chicago Press, Chicago.
Boardman, R.S., Cheetham, A.H., and Rowell, A.J. 1987. Fossil
Invertebrates. Blackwell Scientific Publications, Palo Alto, California.
Find more bryozoan links at the
page of the Zoological Record.