Abstract
Based on new studies of the types and of putative conspecific specimens from various localities in the Indian and Pacific oceans, Porolithon craspedium and Porolithon gardineri were reaffirmed as distinct species. Examining solely morpho-anatomical data, the types of P. castellum and P. marshallense were found to match the present-day diagnosis of P. craspedium and P. gardineri respectively. It is possible therefore that P. castellum and P. marshallense may respectively be conspecific with P. craspedium and P. gardineri. However, due to a lack of DNA sequencing of the type and/or ‘topotype’ specimens, formal synonymies cannot be proposed and we hope that this study can instead be used to facilitate future research. In contrast to other species from the genus, mature P. craspedium is massive and mountain-like, bearing broad individual to fused vertical columns, while P. gardineri is fruticose with narrow terete, loosely dichotomously branched, predominantly unfused protuberances. Species of Porolithon are ecologically very important and are now well established as principal cementers and primary reef frame-builders of coral reefs across the globe. Additionally, P. colliculosum and P. orbicularis where shown to conform instead to the current characterisation of Spongites and have here been duly transferred to that genus.