Family OCYTHOIDAE

Museums

Museum list

Regional Maps

Family OCYTHOIDAE

Compiler and date details

C.C. Lu, National Chung Hsing University, Taichung, Taiwan

Introduction

The pelagic octopus of this monotypic family exhibits extreme sexual dimorphism in size. Females attain large size, up to 350 mm in mantle length (ML); the males are dwarf, probably not exceeding 30 mm ML (Roper & Sweeney 1976), and often live in the test of pelagic salps. The body of these animals is round or oval with long arms. The ventral mantle surface of the adult females bears a reticulate sculpture of ridges and tubercles. In males the hectocotylisation affects the entire third right arm; it develops in a pouch and is detachable.

Ocythoe tuberculata was described by Rafinesque in 1814 from a specimen captured in the Mediterranean Sea. Gray (1849) established the family Ocythoidae to accommodate Ocythoe and Argonauta. Jatta (1896) transferred the genus Ocythoe to the family Argonautidae, which arrangement was then followed by many workers. Robson (1932) re-instated the name Ocythoidae. Roper & Sweeney (1976) reviewed the literature on the species and described the first specimen captured from Australian waters. Lu & Phillips (1985) extended the distributional ranges of the species in Australia to include the open waters off southern Australia. All mature males from Australian waters are smaller than 20 mm ML (Lu 2001).

During mating the hectocotylus, containing the spermatophores, is detached and remains in the mantle cavity of the female. Ocythoe tuberculata produces a large number of eggs: a large female from South Australia is reported to contain 104 000 eggs (Roper & Sweeney 1976). The species is reported to be viviparous, with developing embryos of various stages found in the expanded oviducts (Jatta 1896; Naef 1923).

Ocythoe tuberculata has been observed living in the chamber of the salps, Salpa tilesii and Tethys vagina (Jatta 1896; Hardwich 1970). The animal may move in and out of the test.

Ocythoe tuberculata lives in the epipelagic zone from the surface to about 200 m. It has been found in the diets of lancetfishes Alepisaurux borealis and A. ferox, tunas Thunnus alalunga, T. thunnus and Germon germon, and Risso's dolphin, Grampus griseus (Joubin 1900; Bouxin & Legendre 1936; Berry 1955; Rees & Maul 1956; Rancurel 1970; Iverson 1971; Pinkas 1971).

Ocythoe tuberculata is known to occur in the subtropical and temperate waters of the Pacific and Atlantic Oceans. No specimen has been reported from the tropical waters between 20°N and 20°S and the Indian Ocean (Roper & Sweeney 1976). In Australian waters, the species has been recorded in the diets of hammerhead sharks off New South Wales (Dunning et al. 1993) and has been captured from the open waters of New South Wales to southern Tasmania and the Great Australian Bight, Western Australia (Lu 2001).

Diagnosis

The body is firm, thick, and muscular. The ventral mantle surface in females bears tubercles and ridges in a reticulate pattern. The mantle locking apparatus is well developed and complex. A single ventral pair of water pores is present on the head. The web connecting all arms is very shallow to nearly absent. Arm suckers are biserial. Pronounced sexual dimorphism occurs: males are dwarf, often residing in the pallial chamber of pelagic salps. The entire right arm III is hectocotylised and develops within a stalked pouch; it is detachable in the mature male. Females are large at maturity. The shell vestige is absent.