Redescription of Amphioctopus ovulum (Sasaki, 1917) (Cephalopoda : Octopodidae) and comparative morphological analyses among three species of violet-ringed octopods

Abstract

Amphioctopus ovulum (Sasaki, 1917) is a small to moderate-sized octopus, which can be identified by the iridescent violet ring present in the dark ocellus on the web between the bases of arms II and III. Comprehensive taxonomic review is required to fully characterise this species because the syntypes are missing and the description is insufficiently complete for modern octopod taxonomy. In this study, the species A. ovulum is redescribed with morphological and morphometric characters of 18 specimens collected from the coastal waters of China. The distribution of A. ovulum extends from the Gulf of Thailand, through Cambodia, Vietnam, Philippines, through the South China Sea and the East China Sea to Japan. The swollen terminal organ diverticulum and long spermatophores make it possible to distinguish A. ovulum clearly from A. rex and A. neglectus, species with similar morphological characters of violet rings. Moreover, three species of violet-ringed octopods were clearly differentiated by sequences of the partial mitochondrial genes COI and COIII. Three monophyletic clades resolved in phylogenetic trees. Amphioctopus rex and A. neglectus clustered into a sister taxon, and clustered with the remaining Amphioctopus species.