Chaetetes sp.

Initially classified as corals (suborder Tabulata) due to their tabulate skeleton, Chaetetes has undergone numerous reclassifications, reflecting significant challenges in its phylogenetic placement. Early studies associated it with bryozoans, corals, algae, and even hydrozoans. Modern consensus now identifies Chaetetes as a hypercalcified demosponge within the phylum Porifera.

Chaetetes’ skeleton comprises contiguous tubules with shared walls, a trabecular microstructure, and tabulae (horizontal partitions) - features once thought exclusive to corals. Fossil specimens show a lack of spicules, typical for some modern sponges, complicating its classification further.

Chaetetes is closely related to modern hypercalcified demosponges, such as Merlia normani, Acanthochaetetes wellsi and Ceratoporella nicholsoni, found in cryptic reef environments. These species share structural traits like calcareous skeletons, filled tubules, and tabulae, supporting their link to ancient Chaetetes.