Bryozoa - Taxonomy and Evolution

Taxonomy and Evolution

The phylum was originally called "Polyzoa", but this name was soon replaced by Ehrenberg's term "Bryozoa". The name "Bryozoa" was originally applied only to the animals also known as "Ectoprocta", in which the anus lies outside the "crown" of tentacles (based on the Ancient Greek prefix ἐκτο meaning "outside" and word πρωκτος meaning "anus"). After the discovery of the Entoprocta, in which the anus lies within a "crown" of tentacles (based on the Ancient Greek prefix ἐντο meaning "inside" and word πρωκτος meaning "anus"), the name "Bryozoa" was used at phylum level to include the two classes Ectoprocta and Entoprocta. However, in 1869 Hinrich Nitsche regarded the two groups as quite distinct for a variety of reasons, and coined the name "Ectoprocta" for Ehrenberg's "Bryozoa". Despite their apparently similar methods of feeding, they differed markedly anatomically; in addition to the different positions of the anus, ectoprocts have hollow tentacles and a coelom, while entoprocts have solid tentacles and no coelom. Hence the two groups are now widely regarded as separate phyla, and the name "Bryozoa" is now synonymous with "Ectoprocta". This has remained the majority view ever since, although most publications have preferred the name "Bryozoa" rather than "Ectoprocta". Nevertheless some notable scientists have continued to regard the "Ectoprocta" and Entoprocta as close relatives and group them under "Bryozoa".

The ambiguity about the scope of the name "Bryozoa" led to proposals in the 1960s and 1970s that it should be avoided and the unambiguous term "Ectoprocta" should be used. However, the change would have made it harder to find older works about in which the phylum was called "Bryozoa", and the desire to avoid ambiguity, if applied consistently to all classifications, would have necessitated renaming of several other phyla and many lower-level groups. In practice, zoological naming of split or merged groups of animals is complex and not completely consistent. Works since 2000 have used various names to resolve the ambiguity, including: "Bryozoa", "Ectoprocta", "Bryozoa (Ectoprocta)", and "Ectoprocta (Bryozoa)". Some have used more than one approach in the same work.

The common name "moss animals" is based on the Greek βρυόν (moss) and ζῷα (animals), and refers to the mossy appearance of encrusting species.