Some Old and New Genera of Octopus

抄録

Two old, one new and two current genus names are discussed. The old names are Schizoctopus Hoyle, 1886, for which a type species is here designated, and Tritaxeopus Owen, 1881, which is here associated with the ‘Octopus horridus group’ of species. The two current genus names concern two species of octopus with males hectocotylized on the third left arm: Scaeurgus unicirrhus (delle Chiaje in d’Orbigny, 1841) and Pteroctopus tetracirrhus (delle Chiaje, 1830). The type species of the genus names Scaeurgus and Pteroctopus have been identified as synonyms (rendering these genus names synonyms, also) but approval of an unchallenged redesignation of the type species of Scaeurgus provides an appropriate solution to this problem that would best maintain taxonomic stability.
A new genus name is proposed for the species Octopus januarii Hoyle, 1885, which was previously placed in Benthoctopus Grimpe, 1921. This follows the recent identification of the type species of three genera (Bathypolypus, Benthoctopus and Atlantoctopus, all described by Grimpe, 1921) as belonging to a single genus (excluding Octopus januarii), of which Bathypolypus is the senior synonym. It is here observed that the species closest in morphology to Hoyle’s ‘Octopus’ januarii appears to be ‘Octopus’ longispadiceus (Sasaki, 1917), although the former has no ink sac while the latter has. The common features of these two species include close similarities in the internal structure of the male pseudophallus. Comparisons are made with structural features of the pseudophallus in Enteroctopus dofleini (Wülker, 1910), ‘Octopus’ hongkongensis Hoyle, 1885, and ‘O.’ conispadiceus (Sasaki, 1917), and it is suggested that all five species may be related at the subfamily level.