Bryozoa

Bryozoa
A freshwater bryozoan
Scientific classification
Kingdom:	Animalia
Superphylum:	Lophotrochozoa
Phylum:	Bryozoa
Classes
Stenolaemata; Gymnolaemata; Phylactolaemata

Bryozoans, also known as the Polyzoa, Ectoprocta or moss animals, are a phylum of small aquatic animals living in colonies. The colonies usually have a skeleton of calcium carbonate. Bryozoans have a long fossil history, starting in the Ordovician. In their life-style they resemble the polyps which form coral. They generally like warm, tropical waters but live all over the world. There are about 5,000 living species, and 15,000 fossil species are known.^[1]

The colonies are formed by tiny (~0.2mm) members called zooids.^[2] They secrete tubes, usually of lime (CaCO₃), sometimes of chitin, an organic compound. The zooids in a colony are all clones, produced by asexual reproduction. Despite this, most species produce different morphs: zooids with different functions.^[3]

All bryozoa have a lophophore. This is a ring of ten tentacles surrounding the mouth, each tentacle covered with cilia. When feeding, the zooid extends the lophophore outwards; when resting it is withdrawn into the mouth to protect it from predators.

1. ↑ Clarkson E.N.K. 1998. Invertebrate palaeontology and evolution. 4th ed, Blackwell, Oxford. Chapter 6 Bryozoans, p143.
2. ↑ The word 'zooid' is pronounced zö-oid, not like 'zoo'.
3. ↑ Just as in many animals, cells with the same basic genetics can form different tissues which have different functions. This is done by epigenetics, where genes are switched on and off differently in different tissues.