Unusual Burgess Shale Choia Sponge Assemblage

Description: This is an as unusual 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. Desmosponges skeletons are composed of sponging fibers and/or siliceous spicules. Sponges are known from the late Precambrian, with few localities contributing to the fossil record over time. The Burgess Shale Fauna is one such fossil lagerstatte. The specimen is a member of the type genus of the Family Choiidae, and has an unusual hat-like shape. It is thought to have lain on the bottom convex side up as seen in the restoration. This species is one of 2 known from the Burgess, while the genus is also known from the roughly contemporary deposits of Utah as well as the older Chengiang Biota (see my other offers for a Chengjiang example). This one displays no less than FIVE examples of the type. Even single examples are rare; for every 1000 specimens from the Burgess Shale, less than TEN are Choia. I have included a negative image to make the individuals easier to distinguish. Since the location has been declared a World Heritage site, only specimens from old collections such as this are available.