Paracrinoidea

Comarocystites punctatus

• North America
• Australia
• Europe (Scotland, Estonia)

The Paracrinoidea are an extinct class of echinoderms, which is fossil evidence mainly from the Mittelordovizium North America. The last safe forms of group come from the Oberordovizium of Scotland, finds unsafe assignment is also from the Lower Devonian of the United States.

Features

The Paracrinoiden were marine, sessile organisms such as crinoids were sitting on a structured handle.

The capsule-like body ( the theca ) of the Paracrinoiden is only one to a few centimeters in size. It is pear - shaped or lens- and often unbalanced. The Thekaoberfläche is arrayed or irregular flakes covered, which are provided on its inside with channels and / or pores. The mouth is situated on the surface of the theca, little off the center. The anus is located on the side of the theca.

From there run two Ambulacralrinnen which bifurcate in some forms and structure the theca in a front and a back side. The Ambulacralrinnen put in two ( at ungegabelten Ambulacralrinnen ), three ( with one-sided fork ) or four arms ( with bilateral bifurcation ) away. The arms are from among the fossil specimens of the theca or lie on, are hollow inside and with attachments ( pinnules ) provided. The homology of these pinnules with those of crinoids is controversial. Lying on the arms of the theca, so they are often bent S-shaped and provided with laterally extending notches, where probably the food was transported.

Way of life

The Paracrinoiden ate probably as suspension feeders and planktonic organisms filtered from the passing water.