A taxonomic position of Palaeoa plysina krotov, 1888

An enigmatic organisms Palaeoaplysina were first described by P. I. Krotov at the 1888 year. Since then their taxonomic position repeatedly have been revised. At variously times Palaeoaplysina were refered to sponges, hydrozoans, green codiacean algae and red algae. Hydrants were founded in a microbial matter on a surface of skeletons show the Hydrozoan origin. The Palaeoaplysina composed an upper (consumer) part benthic communities of trophic pyramid. It had indicated mesotrophic surrounding waters.