Amphidiscosida


Amphidiscosida is an order of hexactinellids. 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 : amphidiscs. Amphidiscs are rod-like spicules with an equal-sized umbel at each end. The skeleton is primarily formed by megascleres. In living species, most megascleres are pentactinal, though fossil species often have a more diverse set of megascleres. Amphidiscosids are often covered with prostalia, formed by single-rayed spicules. In a few species, basalia in the lower part of the body are bundled together to suspend the body above the seabed as an anchoring structure.
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