Abdopus

Abstract: The tropical Indo-West Pacific region contains a distinctive group of small to moderate-sized octopuses referred to in the past as the Octopus horridus species-group. Member species are found primarily on intertidal reef flats. 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 acting as a decoy to predators and aiding escape. Lost arms regenerate within 2–3 months. Attributes of this group of octopuses are described and the subgenus Abdopus, subgen. nov. is here coined to define this group. Historically, many members of this subgenus have been incorrectly identified as Octopus 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.) are described. A number of additional, as yet undescribed, species occur throughout the Indo-West Pacific region. Certain earlier works have linked other octopus genera and species with members of this subgenus on the grounds of long arms and arm autotomy. Significant differences occur in the morphologies of these taxa and the nature of the arm autotomy processes. It is proposed that these groups have evolved independently and that arm autotomy has arisen more than once amongst the octopuses. The restriction of the subgenus Abdopus to the tropical Indo-West Pacific region suggests relatively recent origins and radiation.

Abstract: The ability to autotomise and regenerate body parts as a means of escaping predation or renewing damaged tissues has evolved in several animal groups. Some octopuses belonging to the genus Abdopus are known for a high frequency of arm loss and their capacity to regenerate arms. I investigated the mating behaviour and the incidence of arm loss in a shallow-water Abdopus sp. in the wild. Mating occurred at night and at low tide. The male octopus tracked and copulated by repeatedly stretching the hectocotylised arm into the female’s mantle cavity during mating bouts, mostly while the mated female actively moved to forage at the same time. Relatively smaller males adopted sneaking tactics in which they stayed around a mating pair and sometimes gained opportunistic copulations with the female. A significant positive relationship between the body weights of the male and female in each mating pair was detected. Moreover, the proportion of sneaker males that had lost at least one arm prior to mating and t...

Abstract: Female octopuses are thought to copulate with multiple males and store sperm for months prior to spawning, a generalization that has led to hypotheses of strong sperm competition throughout the family. Their diversity, and the difficulty in observing many octopus species in the wild, force indirect tests of this generalization. Male reproductive effort, already high in these generally semelparous animals, is predicted to increase further with sperm competition. Hypothesized functional constraints on the spermatophores that males build to transfer sperm could mean that selection impacts spermatophore number more than morphology. To test whether the number of spermatophores could indicate differences in octopodid biology, the greatest number of spermatophores carried by one individual, and longest spermatophore and mantle lengths were compiled for 74 species. Differences in number were predicted to be independent of differences in specimen availability, related species were predicted to have simila...

Abstract: Difficulties in elucidating the evolutionary history of the octopods have arisen from problems in identifying informative morphological characters. Recent classifications have divided the largest group, the incirrate octopods, into five groups. These include the pelagic superfamily Argonautoidea and three gelatinous pelagic families (Vitreledonellidae, Bolitaenidae, Amphitretidae). All benthic incirrate octopods have been accommodated in the family Octopodidae, itself divided into four subfamilies, Octopodinae, Eledoninae, Bathypolypodinae and Graneledoninae, which are defined by the presence or absence of an ink sac, and uniserial or biserial sucker arrangements on the arms. We used relaxed clock models in a Bayesian framework and maximum likelihood methods to analyse three nuclear and four mitochondrial genes of representatives from each of the previous subfamilies. Strong evidence indicates that the family Octopodidae is paraphyletic and contains the gelatinous pelagic families. The subfamilies of Octopodidae recognised in earlier works do not reflect evolutionary history. The following clades were supported in all analyses: (1) Eledone/Aphrodoctopus, (2) Callistoctopus/Grimpella/Macroctopus/Scaeurgus, (3) Abdopus/Ameloctopus/Amphioctopus/Cistopus/Hapalochlaena/Octopus, (4) Enteroctopus/Muusoctopus/Vulcanoctopus, (5) Vitreledonella/Japetella, (6) Southern Ocean endemic and deep-sea taxa with uniserial suckers. These clades form the basis for a suite of taxa assigned family taxonomic rank: Amphitretidae, Bathypolypodidae, Eledonidae, Enteroctopodidae, Megaleledonidae and Octopodidae sensu nov. They are placed within the superfamily Octopodoidea.