Cystoidea

Cystoids are an extinct class of Echinodermata that lived attached to a stem in the sea floor and is distinguished from other echinoderms by open triangular pores. Superficially they look like the Crinoids but they had bodies of ovoid shape and not formed like a glass. The mouth was positioned in the upper pole of the body, with the opposite end attached to the substrate, often by a stem, although there were also species without stems. The anus stayed on one side of the body. Five or sometimes three areas of the ambulacral system existed along the outside of the body, radiating outwardly from the mouth. A number of tentacles were either around the mouth or projecting out into a row from the area of ​​the ambulacral system, depending on the species.

Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 1008-1009. ISBN 0-03-056747-5. 

Clarkson, E.N.K. (1998). Invertebrate Paleontology and Evolution. Oxford, UK: Blackwell Science. p. 262. ISBN 0-632-05238-4. 

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