Abstract

The monotypic Burgess Shale sponge genus Takakkawia Walcott, 1920, has been previously assigned to the Protomonaxonida, despite showing several unique features. A reassessment of the genus, including restudy of previously described material and the addition of new material that includes partially disarticulated specimens, has allowed a greatly modified understanding of its structure. The sponge possessed four primary columns (each divided into two) of highly modified spicules, with an outer organic layer extended into a unique, complex flange that shows a fine microstructure. The flanges within one column overlap to give the impression of radial fins, and each column is surmounted by an enlarged marginal spicule of similar morphology. Multi-rayed spicules are present both within the primary column architecture and as marginalia lining the osculum. The architecture most closely resembles Metaxyspongia Wu et al., 2005, which is placed into the Takakkawiidae. This restudy supports an interpretation of the family as a very early-branching sponge lineage, diverging within the early stem group of Silicea or prior to the separation of Calcarea and Silicea.

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