Paracrinoidea

Paracrinoidea
	Comarocystites punctatus
Temporal occurrence
	Middle Ordovician to Lower Devonian?
	468 to? Million years
Locations
	North America; Australia; Europe ( Scotland , Estonia );
Systematics
	Tissue animals (Eumetazoa)
	Bilateria
	Neumünder (Deuterostomia)
	Echinoderms (Echinodermata)
	Paracrinoidea
Scientific name
	Paracrinoidea
	Regnéll , 1945

The Paracrinoidea are an extinct class of echinoderms , which has been found fossilized mainly from the Central North Novice of North America. The last certain forms of the group come from the Upper Ordovician of Scotland, there are also finds of uncertain allocation from the Lower Devonian USA. The taxon was introduced in 1945 by the Swedish geologist Gerhard Regnéll .

features

The paracrinoids were marine, sessile organisms that sat like sea lilies on an articulated stem.

The capsule-like body (theca) of the paracrinoids is only one to a few centimeters in size. It is pear-shaped to lenticular and often asymmetrical. The counter surface is covered by regularly arranged or irregular platelets which are provided with channels and / or pores on their inside. The mouth lies on the surface of the theka, slightly off the center. The anus lies on the side of the theka.

From there, two ambulacral channels run , which fork in some shapes and divide the theca into a front and a back. The ambulacral gutters continue in two (for non-bifurcated ambulacral gutters), three (for one-sided bifurcation) or four arms (for double-sided bifurcation). The arms of the fossil specimens protrude or lie on the theka, are hollow on the inside and have appendages (pinnulae). The homology of these pinnulae with those of the sea lilies is controversial. If the arms of the theka lie on, they are often bent into an S-shape and provided with laterally running notches, in which the food was probably transported.

Way of life

The paracrinoids probably fed on as suspension eaters and filtered planktonic organisms from the water flowing by.

literature

Bernhard Ziegler: Introduction to Paleobiology, Part 3, Special Paleontology, Worms, Arthropods, Lophophorates, Echinoderms . Schweizerbartsche Verlagbuchhandlung, Stuttgart 1998 ISBN 3-510-65179-0

Individual evidence

↑ G. REGNELL: Non-crinoid Pelmatozoa from the Paleozoic of Sweden. In: Meddelanden från Lunds Geologisk-Mineralogiska Institution , Vol. 108, pp. 1–255, 1945.

Web links

Commons : Paracrinoidea - collection of images, videos and audio files

The Paleobiology Database: Paracrinoidea

[Regnéll,_1945-1] G. REGNELL: Non-crinoid Pelmatozoa from the Paleozoic of Sweden. In: Meddelanden från Lunds Geologisk-Mineralogiska Institution , Vol. 108, pp. 1–255, 1945.