Earliest ontogeny of the Silurian orthotetide brachiopod Coolinia and its significance for interpreting strophomenate phylogeny

Well-preserved juvenile specimens of the orthotetide brachiopod Coolinia pecten (Linnaeus, 1758) from the Silurian of Gotland, Sweden, demonstrate evidence of a planktotrophic larval habit. Larval shell morphology indicates the absence of a pedicle sheath: this character is otherwise typical of derived billingsellides, strophomenides and productides, which form the conventional strophomenide clade. The presence of a rudimentary colleplax structure in the larval shell of Colinia suggests instead a phylogenetic link to chiliate brachiopods and the enigmatic genus Salanygolina. This relationship suggests an early divergence of rhynchonellate and strophomenate brachiopods.