Amphidiscosida

Amphidiscosida (sometimes spelled Amphidiscosa)^[2][3] is an order of hexactinellids (glass sponges). The Amphidiscosida are commonly regarded as the only living sponges in the subclass Amphidiscophora.^[4][5]

Amphidiscosida Temporal range: Cambrian–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Specimen of Pheronema carpenteri on exhibit in Naturmuseum Senckenberg
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Porifera
Class:	Hexactinellida
Subclass:	Amphidiscophora Schulze, 1886
Order:	Amphidiscosida Schrammen, 1924[1]

Hyalonema (family Hyalonematidae, B) and an amphidisc microsclere (A, right) in a collage of hexactinellids.

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.^[2] 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.^[2][6]

The oldest fossilized amphidiscs are from the Carboniferous, but sponge fossils with spicules similar to Amphidiscosida have existed since the Cambrian period.^[2][3] Three families still flourish in deep marine waters today.

Families

• Hyalonematidae Gray, 1857^[7]
• Monorhaphididae Ijima, 1927^[8]
• †Pattersoniidae Miller, 1889 [Middle Ordovician–Upper Ordovician]^[2]
• †Pelicaspongiidae Rigby, 1970 [Lower Ordovician–Triassic]^[2]
• Pheronematidae Gray, 1870^[9]
• †Stiodermatidae Finks, 1960 [Lower Cambrian–Permian]^[2][3]