Diploporita

Diploporita is an extinct class of blastozoan that ranged from the Ordovician to the Devonian. These echinoderms are identified by a specialized respiratory structure, called diplopores. Diplopores are a double pore system that sit within a depression on a single thecal (body) plate; each plate can contain numerous diplopore pairs.

The diploporitans likely represent a polyphyletic group. The evidence for this claim lies within the highly morphologically diverse body plans of the diploporitans: there are major differences in the makeup of the attachment structure (e.g., stem or holdfast), in the makeup of the feeding grooves, and even major differences in the construction of the group-defining diplopore respiratory structures. The only phylogenetic analysis of Diploporita to date indicates that Diploporita is not a natural evolutionary group. Rather, Diploporita is an artificial grouping based on the presence of diplopores, that have re-evolved multiple times throughout the echinoderm evolutionary tree.