Bryozoa

BRYOZOA

Moss or lace animals

(Greek.bryon = moss + zoon = animal)
Many bryozoans are gathered in small tuffed colonies attached to objects in shallow seawater. All species are colonial with the individuals being extremly small.

A lateral view of a portion of a colony encrusting bryozoans.

A lateral view, of a portion of a colony, of encrusting bryozoans.

Some appear similar to hydroids or corals but their internal structure is more complex. Their form suggested the name moss animals.

An individual of a colonial bryozoan with a retracted lophophore.

An individual of a colonial bryozoan with a protruded lophophore (the arrows indicate the flow of water).

Characteristics:

1. Symmetry is bilateral. There occurs no segmentation. Triploblastic.

2. Colonial. The individuals are minutely small, each in its own housing (zooecium). Polymorphism in some.

3. Digestive canal complete(U-shaped). The mouth is surrounded by a retractile lophophore with ciliated tentacles. The anus opening outside the lophophores.

4. Coelom well developed into two parts. No circultory or respiratory organs present.

5. No nehpridia.

6. A nerve ganglia between mouth and anus.

7. The sexes are usually united and gonads are formed from peritoneum. The eggs are feritilized in the coelom or externally. The eggs are usually brooded in a modified zooecium (ooecium) among the tentacles, in the coelom or in a partition of reproductive individual. The larva is a trochopore. Colonies are formed by asexual budding.

A colony of bryozoans.