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Phylum Bryozoa

 

Bryozoa are colonial animals living mostly in marine water but few kinds inhabit fresh water. They are very small, less than 1 mm in length and occur at all depths. Bryon = moss (they form moss like growths).

 

Anatomical features:

The bryozoan animal is called zooid. It has a bag like body form. At the upper end there are tentacles which are joined at their base to a fleshy ring called lophophore.

The ring of lophophore surrounds the mouth this mouth leads to a digestive U-shaped tube consisting of an Esophagus, a stomach and an intestine. The intestine ends with an anus, which lies beside the mouth but outside the ring of tentacles.

 

Q. What is the similarity between Bryozoa and Coelenterates?

Which one is more advanced?

 

Reproduction:

(bisexual) or each individual may have single type.

 

Skeleton :

The skeleton of bryozoa is external and made up of CaCo3, usually calcite, sometimes aragonite or both. The skeleton of one individual is called Zooecium and that of the colony is called Zoarium.

 

Mode of life:

 

Factors controlling the distribution of bryozoa:

Bryozoa are found at all depths from the shoreline down to the abyssal zone. Their distribution is controlled by the following factors:-

  1. Temperature: most bryozoa have narrow range of temperature

    2. tolerance.

  2. Wave action: since they can easily damaged.

  3. Substrate: they need a hard substrate upon which the larvae can

    4. settle. At greater depths the substrate is composed

    of soft fine mud which is not suitable for fixation

    of bryozoa.

  4. Salinity: bryozoa are rare at river mouths since salinity is low and

suspended fine sediments are much.

 

Geologic importance:

Bryozoa range from Ordovician to the present day. Some have short range and wide geographic distribution and so good index fossils for correlation.

They are important as reef-builders together with tabulate corals during the Paleozoic.