Amphidiscosida

{{Short description|Order of sponges}}

{{Automatic taxobox

| fossil_range = {{Fossil range|Cambrian|Recent}}

| image = Pheronema carpenteri - Naturmuseum Senckenberg - DSC02149.JPG

| image_alt = "Pheronema carpenteri" on exhibit in Naturmuseum Senckenberg

| image_caption = Specimen of Pheronema carpenteri on exhibit in Naturmuseum Senckenberg

| parent_authority = Schulze, 1886

| taxon = Amphidiscosida

| authority = Schrammen, 1924Schrammen, A. (1924). Die Kieselspongien der oberen Kreide von Nordwestdeutschland. Volume 3. Berlin: Gebrüder Borntraeger.

| subdivision_ranks = Families

| subdivision =

}}

File:Hexactinellida diversity.png (family Hyalonematidae, B) and an amphidisc microsclere (A, right) in a collage of hexactinellids.]]

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, available [https://journals.ku.edu/InvertebratePaleo/issue/view/455 here]. {{ISBN|0-8137-3131-3}}.{{Cite journal |last=Li |first=Lixia |last2=Reitner |first2=Joachim |last3=Gong |first3=Fangyi |last4=Yan |first4=Guanzhou |last5=Wu |first5=Rongchang |date=2023-01-02 |title=A new stiodermatid (Hexactinellida, Porifera) from the latest Ordovician of Anhui, South China and its significance for searching the missing link between the Cambrian and late Palaeozoic stiodermatid lineage |url=https://doi.org/10.1080/08912963.2021.2024180 |journal=Historical Biology |volume=35 |issue=1 |pages=116–126 |doi=10.1080/08912963.2021.2024180 |issn=0891-2963|url-access=subscription }} is an order of hexactinellids (glass sponges). The Amphidiscosida are commonly regarded as the only living sponges in the subclass Amphidiscophora.{{cite web |title=Hexactinellida: Fossil Record |url=http://www.ucmp.berkeley.edu/porifera/hexactinellidafr.html |website=UCMP Berkeley}}{{Cite journal |last=Reid |first=R.E.H. |date=1961 |title=Notes on Hexactinellid sponges—III. Seven Hexactinosa |url=http://dx.doi.org/10.1080/00222936108651201 |journal=Annals and Magazine of Natural History |volume=4 |issue=48 |pages=739–747 |doi=10.1080/00222936108651201 |issn=0374-5481|url-access=subscription }}

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, Volume 2: Introduction to the Porifera, xxvii + 349 p., 135 fig., 10 tables, 2003, available [https://journals.ku.edu/InvertebratePaleo/issue/view/454 here]. {{ISBN|0-8137-3130-5}}.

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