Large Unknown Desmosponge Fossil from Chengjiang China

Description: This is an unknown member of the Desmospongia, the most diverse of modern-day sponges. Greater than 90% of the extant 5,000 known species of sponges are desmosponges. Such a representation in the fossil record is not maintained where less than half the known genera are of this type, a consequence of the fact that the skeletons do not fossilize readily. Desmosponge skeletons are composed of spongin fibers and/or siliceous spicules. Sponges are known from the late Precambrian, with few localities contributing to the fossil record over time. The Chengjiang Biota is one such fossil lagerstatte. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid-like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day. This one has its affinities with Choiaella, and is placed within the Choiidae.