Family ONYCHOTEUTHIDAE

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Family ONYCHOTEUTHIDAE

Compiler and date details

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

Introduction

Members of the family Onychoteuthidae Gray, 1849 are medium to very large oceanic squid (up to 2 m mantle length (ML)), with the mantle strong, muscular and torpedo-shaped. They are common in all oceans. Worldwide five genera with some 12 nominal species are known, some of which may represent complexes of closely similar species. Seven species from four genera have been recorded from Australia (Lu & Phillips 1985; Lu, unpublished data).

The first record of the family in Australian waters was Gould’s (1852) description of Onychoteuthis rutilis, from off Sydney, New South Wales. Allan (1945) assigned larval onychoteuthids from off New South Wales to this species. Additional species have been recorded from the Australasian Region by Rancurel (1970, 1976), Nesis (1979) and Rancurel & Okutani (1990). With the exception of Onykia, all currently recognised genera occur in Australian waters, including the waters around the Australian Antarctic Territory, but their distributions are poorly delineated (Lu & Phillips 1985).

Onychoteuthids are oceanic, but are occasionally encountered in continental slope waters where they are sometimes caught in demersal trawls. They feed on a broad range of fish, crustaceans including krill, other pelagic molluscs and squids, and are at least partly cannibalistic. Known predators include lancetfish and tunas, whales, dolphins, seals and albatrosses (Rancurel 1970, 1976; Clarke 1983).

Onychoteuthid reproductive organs are typically oegopsid, and show little variation within the family. Hectocotylisation has not been observed in any males, although Gilly et al. (1986) noticed that in Moroteuthis from off California, males have a prominent fleshy keel on the ventral arms only. Spermatophores are apparently introduced into the mantle of female Onychoteuthis and Moroteuthis from the elongated penis, through a longitudinal cut made midway between the head and fins of the female, using the beak or perhaps the tentacular hooks. Mature inseminated females of Onychoteuthis borealijaponica Okada, off Japan, display a bright orange colour over the viscera and mantle (Clarke 1980; Murata 1982).

Little is known about the longevity and growth of onychoteuthids. The biology is relatively well known for Onychoteuthis borealijaponica only. This species occurs in the temperate waters of the north-west Pacific, reaches in excess of 300 mm ML, and spawns from late autumn to winter in warmer subtropical waters to the south. Larvae have been found in the upper 150 m of the water column but not at the surface. Growth in adults was estimated at up to 20 mm per month and the life span at approximately one year. Females are generally larger than contemporary males (Okutani & Murata 1983). Off California, Moroteuthis is believed to spawn in submarine canyon areas on the upper continental slope (Gilly et al. 1986). From examination of material collected from sperm whale stomachs, Clarke (1980) concluded that Moroteuthis robsoni Adam spawns on the lower continental slope (2500 m) in the austral autumn off South Africa. Clarke suggested that the young grow to more than 500 mm ML over a period of approximately two years prior to a single spawning, followed by wasting of the body musculature, and death. According to Kubodera et al. (1998) the genus Chaunoteuthis represents spent individuals of other genera of this family, thus this is considered an invalid genus.

Onychoteuthids are schooling species. Juvenile Onychoteuthis are able to glide above the surface to escape predators; sometimes they are found on the decks of vessels, presumably accidently landing there when gliding. Off Japan, Onychoteuthis borealijaponica appears to make a north-south migration from feeding grounds to the warmer spawning grounds (Okutani & Murata 1983); whether such migrations are typical of temperate onychoteuthids is unconfirmed. Little information regarding the vertical distribution of any onychoteuthid species is available. Onykia species share with the much larger ommastrephid, Ommastrephes bartrami, and some epipelagic octopods, the deep blue, dorsal day coloration characteristic of neuston species in general (Roper & Young 1975). The presence of Onykia in the stomachs of lancetfish and yellowfin tuna further confirms its epipelagic distribution (Rancurel 1970, 1976; Fujita & Hattori 1976). Clarke and Lu (1974) recorded juvenile Onychoteuthis banksi from between 100 and 1250 m in the North Atlantic.

Diagnosis

The family is characterised by a simple straight funnel locking cartilage, biserial suckers on the arms and biserial hooks on the tentacular clubs, except in the genera Onykia and Kondakovia and the juvenile Moroteuthis, which have two rows of marginal suckers also present on the tentacular clubs. The buccal connectives attach to the ventral border of the ventral arms, and visceral light organs are present in the genus Onychoteuthis. Hectocotylisation is absent in males. The large muscular fins are generally rhomboidal and in some species of Moroteuthis Verrill and Ancistroteuthis Gray; fins and mantle attenuate posteriorly. Numerous distinctive pleats are present in the neck region in Onychoteuthis, and the skin of Moroteuthis and Kondakovia often contains subcutaneous papillae and ridges. In some of the larger species, lateral arms have swimming keels.