Amphidiscosida (sometimes spelled Amphidiscosa)''Treatise on Invertebrate Paleontology'' Part E, Revised. Porifera, Volume 3: Classes Demospongea, Hexactinellida, Heteractinida & Calcarea, xxxi + 872 p., 506 fig., 1 table, 2004, availabl
here
. is an order of hexactinellids (glass

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s). The Amphidiscosida are commonly regarded as the only living sponges in the subclass Amphidiscophora. As the name implies, the Amphidiscosida are characterized by a special type of microsclere (microscopic spicules): amphidiscs. Amphidiscs are rod-like spicules with an equal-sized umbel (a whorl of backswept hooks) at each end. The skeleton is primarily formed by megascleres (large spicules). In living species, most megascleres are pentactinal (five-rayed), though fossil species often have a more diverse set of megascleres. Amphidiscosids are often covered with prostalia (bristles), formed by single-rayed spicules. In a few species, basalia (long rooting bristles) in the lower part of the body are bundled together to suspend the body above the seabed as an anchoring structure.''Treatise on Invertebrate Paleontology'' Part E, Revised.

Porifera Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a Basal (phylogenetics) , basal clade and a sister taxon of the Eumetazoa , diploblasts. They are sessility (motility) , sessile ...

, Volume 2: Introduction to the Porifera, xxvii + 349 p., 135 fig., 10 tables, 2003, availabl
here
. The oldest fossilized amphidiscs are from the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

, but sponge fossils with spicules similar to Amphidiscosida have existed since the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

period. Three families still flourish in deep marine waters today.

Families

* Hyalonematidae Gray, 1857Gray, J. E. (1857). Synopsis of the families and genera of axiferous zoophytes or barked corals. ''Proceedings of the Zoological Society of London'', 25(1), 278–294. * Monorhaphididae Ijima, 1927Ijima, I. (1927). The Hexactinellida of the Siboga Expedition. In Weber, M. (Ed.), ''Siboga-Expeditie'' (1–383). Leiden: E. J. Brill. *† Pattersoniidae Miller, 1889 nowiki/>Middle Ordovician–Upper Ordovician">Middle_Ordovician.html" ;"title="nowiki/>Middle Ordovician">nowiki/>Middle Ordovician–Upper Ordovician] *†Pelicaspongiidae Rigby, 1970 [Lower Ordovician–Triassic] *Pheronematidae Gray, 1870Gray, J. E. (1870). Notes on anchoring sponges (in a letter to Mr. Moore). ''The Annals and Magazine of Natural History'', (34), 309–312. *† Stiodermatidae Finks, 1960 nowiki/>Lower Cambrian–Permian">Lower_Cambrian.html" ;"title="nowiki/>Lower Cambrian">nowiki/>Lower Cambrian–Permian]

References

Hexactinellida Sponge orders {{poriferan-stub