Amphidiscosida Explained

Amphidiscosida (sometimes spelled Amphidiscosa)^{[1] [2]} is an order of hexactinellids (glass sponges). The Amphidiscosida are commonly regarded as the only living sponges in the subclass Amphidiscophora.^{[3] [4]}

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.^[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.

Families

• Hyalonematidae Gray, 1857^[6]
• Monorhaphididae Ijima, 1927^[7]
• †Pattersoniidae Miller, 1889 [<nowiki/>[[Middle Ordovician]]–Upper Ordovician]
• †Pelicaspongiidae Rigby, 1970 [<nowiki/>[[Lower Ordovician]]–Triassic]
• Pheronematidae Gray, 1870^[8]
• †Stiodermatidae Finks, 1960 [<nowiki/>[[Lower Cambrian]]–Permian]

Notes and References

1. 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. .
2. Li . Lixia . Reitner . Joachim . Gong . Fangyi . Yan . Guanzhou . Wu . Rongchang . 2023-01-02 . 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 . Historical Biology . 35 . 1 . 116–126 . 10.1080/08912963.2021.2024180 . 0891-2963.
3. Web site: Hexactinellida: Fossil Record . UCMP Berkeley.
4. Reid . R.E.H. . 1961 . Notes on Hexactinellid sponges—III. Seven Hexactinosa . Annals and Magazine of Natural History . 4 . 48 . 739–747 . 10.1080/00222936108651201 . 0374-5481.
5. Treatise on Invertebrate Paleontology Part E, Revised. Porifera, Volume 2: Introduction to the Porifera, xxvii + 349 p., 135 fig., 10 tables, 2003, available here. .
6. Gray, 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.
7. Ijima, I. (1927). The Hexactinellida of the Siboga Expedition. In Weber, M. (Ed.), Siboga-Expeditie (1–383). Leiden: E. J. Brill.
8. Gray, J. E. (1870). Notes on anchoring sponges (in a letter to Mr. Moore). The Annals and Magazine of Natural History, [4]6(34), 309–312.