robert karl stonjek

EVOLUTION: ON PLACOZOA -- THE SIMPLEST KNOWN ANIMAL

The following points are made by D.J. Miller and E.E. Ball (Current Biology
2005 15:R26):

1) Often described as the simplest known animal, the unassuming marine
placozoan Trichoplax adhaerens is one of a handful of "lower" metazoans that
have so far defied being pigeonholed. The history of Trichoplax and its
relatives has the elements of a scientific mystery story [1]. In 1971, Karl
Grell [2] formally described a new Phylum, the Placozoa, to accommodate two
species that had been reported a hundred years earlier. These were
originally greeted with excitement as "living fossils" representing the
ancestral animal morphology. However, the suggestion that they were, in
fact, modified cnidarian larvae prompted a loss of interest for the next
fifty years. One of the species upon which Placozoa was founded, Treptoplax
reptans, has never been seen since its original description, and is assumed
not to exist; T. adhaerens, on the other hand, appears to be widely
distributed and relatively common in warm marine environments [1]. However,
other than field surveys [3], all that is known about it is based on
aquarium cultures.

2) ....

Full Text at Science Week
http://scienceweek.com/2005/sw050401-1.htm

Posted by
Robert Karl Stonjek