Mesospora elongata sp. nov. (Ralfsiales, Phaeophyceae), a new crustose brown algal species from the Indo-Pacific region

Crustose brown algae have relatively simple morphology and anatomy, and the limited characters were a major obstacle in delineating species of Mesospora (Ralfsiales, Phaeophyceae). The type species, Mesospora schmidtii, was described using material collected in Indonesia. A subsequent study, using material from Japan, was identified as M. schmidtii, but we questioned the identity. Therefore, we analyzed morphological characters as well as the plastid-encoded RuBisCO large subunit (rbcL) and mitochondrial-encoded cytochrome c oxidase subunit 1 (cox1) genes using new material obtained from the type locality (Indonesia) and new material obtained from Japan. The molecular phylogenetic analysis distinguished two clades, one representing material from the type location and the other representing an undescribed species from Japan. Therefore, we described Mesospora elongata sp. nov. to encompass the Japanese material. Morphologically, the two species were very similar (i.e. cryptic species); the only obvious difference was the number of cells. We also discussed Hapalospongidion but we concluded that Mesospora should be a distinct genus based on morphology; gene sequence data will be required for Hapalospongidion before the relationship of the two genera is more thoroughly resolved.