Parazoa are an ancestral subkingdom of animals, literally translated as "beside the animals".
Description [ edit ]
Parazoans differ from their
choanoflagellate ancestors in that they are not microscopic and have differentiated cells. However, they are an outgroup of the animal phylogenetic tree being that they do not have tissues or organs. The only surviving parazoans are the sponges, which belong to the phylum Porifera, and the Trichoplax in the phylum Placozoa.
Parazoa display no body symmetry (are asymmetrical); all other animal groups display some sort of symmetry. There are currently 5000 species, 150 of which are freshwater. Larvae are
planktonic and adults are sessile.
Cladistics [ edit ]
The Parazoa-Eumetazoa split has been estimated at 940 million years ago.
The parazoa group is now considered
paraphyletic. It is not included in most modern [2 ] cladistic analyses. When referenced, it is sometimes considered an equivalent to Porifera. [3 ]
Some authors include
Placozoa, a phylum that consists of only one species, [4 ] , in the division, but they are also sometimes placed in the subkingdom Trichoplax adhaerens Agnotozoa.
References [ edit ]
External links [ edit ]