Australia: The Land Where Time Began

A biography of the Australian continent 

Cambrian Explosion - Chancellorida

The Chancelloriids are a clade from the Cambrian that is now extinct that are believed to have had a feeding system that was sponge-like, that were sessile, bag-shaped or vase-shaped forms with bodies that were hollow and had no organs. Their body wall exteriors were covered with hollow, aragonitic sclerites from which spine-like rays radiated and that were attached to stalks on the surface of the body (Randell et al., 2005). It is believed these sclerites were probably for protection from predators. It is common to find Chancelloriid sclerites in small shelly faunas, and they are often found in archaeocyathan reefs. It has been interpreted that they branched from organisms of sponge grade (Butterfield & Nicholas, 1996), possibly being part of a radiation of sessile benthic forms that used flagella to pump minute plankton for feeding (Sperling, Peterson & Pisana, 2009). Early bilaterians such as Halkieria are known to have had hollow sclerites with basal foramina, however (see Lophotrochozoa below) and such sclerites have been interpreted as a synapomorphy of a distinctive clade, Coeloscleritophora (Porter, 2008). A phylogenetic link between Chancelloriids and bilaterians is suggested by similarities of the skeletal microstructures of the 2 clades (Porter, 2008). It has been argued that both Chancelloriids and bilaterians share these characters, and it is possible they may even be eumetazoan plesiomorphies, therefore the Coeloscleritophorans might represent the lineage that links the early nonbilaterians to bilaterians, though alternatively the characters may have been convergent.

Sources & Further reading

1. Erwin, Douglas H., & Valentine, James W., 2013, The Cambrian Explosion: The Construction of Animal Biodiversity, Roberts & Co., Greenwood Village, Colorado