Gelatinous red algae of the Arabian Sea, including <i>Platoma heteromorphum</i> sp. nov. (Gigartinales, Rhodophyta)

This study reports on the gelatinous red algae of the Arabian Sea (Masirah Island, Oman and Socotra Island, Yemen) belonging to the families Dumontiaceae, Nemastomataceae and Schizymeniaceae. Dudresnaya capricornica, Gibsmithia larkumii, Predaea laciniosa, P. weldii and Titanophora pikeana are new records for the region. The morphological and reproductive features of these species are presented, with emphasis on post-fertilization events. Platoma heteromorphum Schils sp. nov. is described from an upwelling region along the eastern coast of Masirah Island. Based on similarities in morphology and post-fertilization events, this species is closely related to P. ardreanum, P. cyclocolpum (the generitype) and P. izunosimense. The connecting filament initiation in P. heteromorphum is comparable to Titanophora, but the post-fertilization processes observed in P. heteromorphum and T. pikeana clearly demarcate both genera within the Schizymeniaceae. A first impression of the gelatinous red algae in the Arabian Sea suggests a high biogeographical affinity with Australia, but additional records from the Indian Ocean indicate that their distribution may be more widespread than is currently accepted