Revision of the Octopus horridus species-group, including erection of a new subgenus and description of two member species from the Great Barrier Reef, Australia

The tropical Indo-West Pacific region contains a distinctive group of small to moderate-sized octopuses referred to in the past as the Octopus horridu s species-group. Member species are found primarily on intertidal reef flat s. They possess small bodies, long arms and complex skin sculpture and body patterns enabling excellent camouflage. When attacked, these octopuses are capable of autotomising their arms at the base: the writhing severed arm a cting as a decoy to predators and aiding escape. Lost arms regenerate withi n 2-3 months. Attributes of this group of octopuses are described and the s ubgenus Abdopus, subgen. nov. is here coined to define this group. Historic ally, many members of this subgenus have been incorrectly identified as Oct opus horridus, a distinct large-egg species known only from the Red Sea and the northwest Indian Ocean. Seven species are here recognised as belonging in Abdopus, subgen. nov. Two member species from Great Barrier Reef waters (Octopus aculeatus d'Orbigny, 1834 and Octopus capricornicus, sp. nov.) ar e described. A number of additional, as yet undescribed, species occur thro ughout the Indo-West Pacific region. Certain earlier works have linked othe r octopus genera and species with members of this subgenus on the grounds o f long arms and arm autotomy. Significant differences occur in the morpholo gies of these taxa and the nature of the arm autotomy processes. It is prop osed that these groups have evolved independently and that arm autotomy has arisen more than once amongst the octopuses. The restriction of the subgen us Abdopus to the tropical Indo-West Pacific region suggests relatively rec ent origins and radiation.