Family AMPHITRETIDAE

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Family AMPHITRETIDAE

Compiler and date details

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

Introduction

The pelagic octopod of this monotypic family has a gelatinous body enveloped in a thick layer of gelatinous tissue. The eyes are tubular and directed dorsally. The arms are long, bear a single row of suckers, and are connected by a deep web. The mantle aperture is reduced to two small openings lateral to the funnel. The funnel is fused to the mantle.

The Aphitretidae was erected by Hoyle (1886) for a specimen captured in the central Pacific Ocean off Kermedec Island. Thore (1949) reported and described other specimens captured in the Pacific Ocean and Indian Ocean during the Dana Expedition.

The first Australian specimen, captured off Maria Island, Tasmania, was reported by Allan (1945). With further data, Lu & Phillips (1985) extended the distributional range to include the Coral Sea and south-western Tasmania.

Almost nothing is known about the biology of the only member of the family, Amphitretus pelagicus. Thore (1949) reported the mature ovarian eggs to be about 5 x 2 mm and that young of about 7 mm total have the same characteristics as adults. The specimen reported by Allan (1945) had ML 4 mm and total length of 12 mm. Amphitretus pelagicus was found in the gut of Alepisaurus ferox captured in the South West Pacific (Rancurel 1970).

Amphitretus pelagicus is cosmopolitan, found in the tropical and temperate waters of all oceans. There is some evidence that the species undergoes ontogenetic descent, the juveniles smaller than 30 mm total length living in surface waters of less than 150 m and adults and subadults living in the mesopelagic to bathypelagic zones from 150 m to 2000 m (Hochberg et al. 1991).

Diagnosis

The body issac-like and enveloped in a thick layer of gelatinous tissue. The arms are long and are connected by a deep web. The suckers are in a single row. The mantle aperture is reduced to two small openings lateral to the funnel; the funnel is fused to the mantle. The third right arm is hectocotylised, with the ligula long and narrow and calamus short. The eyes are tubular and directed dorsally. There is no shell vestige.