Article: Morphology and phylogenetic significance of the corners and midlines of the conulariid test

The hypothesis that conulariids were closely related to scyphozoan cnidarians is based in large part on interpretations of the morphology of the corners and midlines of the conulariid test. Corners and/or midlines of some or all species of at least ten of the twenty-one currently recognized conulariid genera are internally thickened. Internal midline structures of some or all species of six genera are paired or adaxially bifid. Midlines of one species, Eoconularia amoena Sinclair, exhibit features suggesting the presence of a single carina that bifurcates adaperturally. Species of five genera exhibit internal structures both at the corners and the midlines. In almost all of these taxa, internal structures at the corners are broader and/or higher than associated midline structures. Internal corner and/or midline structures of some members of two genera are seriated. Conulariid corners and midlines show a number of similarities to soft-part and thecal structures located, respectively, at the scyphozoan perradii and interradii. Nearly all of these similarities are uniquely shared by conulariids and scyphozoans, and corroborate Kiderlen's (1937) hypothesis that conulariid midlines were sites of a gastric septum, homologous to the gastric septa of scyphozoans.