Hemidiscellidae

Hemidiscellidae is an extinct family of sponges in the class Hexactinellida (glass sponges) and the subclass Amphidiscophora.^[1] Hemidiscellidae (sometimes known as Microhemidisciidae)^[2] is the only family in the order Hemidiscosa.^[1]

Hemidiscellidae Temporal range: Gzhelian (latest Pennsylvanian) – Cretaceous PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Porifera
Class:	Hexactinellida
Order:	†Hemidiscosa Schrammen, 1924
Family:	†Hemidiscellidae Kling & Reif, 1969
Genera
†Hemidiscella Reid, 1958 †Microhemidiscia Kling & Reif, 1969
Synonyms
Microhemidisciidae Finks & Rigby, 2004

Hemidiscosans are differentiated by the form of their microscleres. Their microscleres, more precisely known as hemidiscs, have the form of a rod with a large umbel (hooked whorl) at one end and a much smaller umbel on the other end. This form of microsclere is intermediate between paraclavules (basic rods present in many sponges) and amphidiscs (rods with umbels of equal size, found in the order Amphidiscosida).^[2]

References

1. Mouro, L. D.; Fernandes, A. C. S.; Rogerio, D. W.; Fonseca, V. M. (2014). "First articulated sponge from the Paleozoic of Brazil, and a new organization of the order Hemidiscosa". Journal of Paleontology. 88 (1): 171–178. doi:10.1666/12-108. ISSN 0022-3360.
2. Treatise on Invertebrate Paleontology Part E, Revised. Porifera, Volume 3: Classes Demospongea, Hexactinellida, Heteractinida & Calcarea, xxxi + 872 p., 506 fig., 1 table, 2004, available here. ISBN 0-8137-3131-3.