Created 19/02/2019
05 Mar
2019
Placozoa: Some good reasons why they are collected in Roscoff and also travel in space

The phylum Placozoa was discovered in 1883 by F.E. Schulze and so far consists of only one officially recognized species, Trichoplax adhaerens.

Bernd Schierwater

The phylum Placozoa was discovered in 1883 by F.E. Schulze and so far consists of only one officially recognized species, Trichoplax adhaerens. Placozoans are irregular disc-shaped benthic animals of a few millimeters in diameter which crawl on hard substrates by ciliary movement or by expansions and contractions of their body. With only six somatic cell types identified to-date, placozoans exhibit the most simple morphology of
a free-living metazoan. Their simplistic bauplan and small genome (less than 100 Mb) has fueled the view that placozoans represent the closest extant surrogate of the last common metazoan ancestor, though molecular evidence for this traditional view is ambiguous. In sharp contrast to the high degree of genetic variability between different lineages, almost no variation on the basic placozoan bauplan has been observed, even at the ultrastructural level. It seems plausible that the most simple design of placozoans does not allow major anatomical deviations. This is in marked contrast to all other non-bilaterian animals (cnidarians, sponges and ctenophores), which exhibit a high morphological diversity. Understanding placozoan biology is further complicated by their enigmatic life cycle...