Family CYCLOTEUTHIDAE

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Introduction

The poorly known family Cycloteuthidae Naef, 1923 includes two apparently mesopelagic genera of medium to large species (less than 600 mm mantle length (ML)): the monotypic Cycloteuthis Joubin, and Discoteuthis Young & Roper. Three species are known from the tropical and subtropical waters worldwide; two species have been recorded from Australian waters.

This family was first described from Australian waters by Clarke (1980) who found specimens of Cycloteuthis akimushkini Filippova (now considered to be a junior synonym of C. sirventi Joubin) among the stomach contents of sperm whales caught off Albany, Western Australia. Subsequently, this genus, and beaks assigned tentatively to ?Discoteuthis, were also found in whales from the Tasman Sea (Clarke & MacLeod 1982). Lu & Phillips (1985) recorded Discoteuthis discus Young & Roper from off the south-eastern Australian coast.

The cycloteuthid mantle is not heavily muscular: a central layer of gelatinous connective tissue lies between thin inner and outer layers of strong circular muscle. The head is also covered with moderately thick, semi-gelatinous tissue (Clarke 1980). In contrast to those of the similarly shaped octopoteuthids, the fins in Discoteuthis are separate and insert directly onto the shell sac of the gladius. In Octopoteuthis, the fins are fused and continuous across the dorsal midline, passing over the shell sac. Corresponding differences in the structure of the gladius are also present; in Octopoteuthis, this is thin and fragile, while in Discoteuthis, the gladius is a very thick, rigid supporting structure (Young & Roper 1969).

Little is known about the biology of any species, save that cycloteuthids form part of the diet of sperm whales in the Australasian region (Clarke 1980; Clarke & MacLeod 1982) and elsewhere (Clarke 1983).

The few records of this family provide little conclusive information regarding their vertical distribution. All three species recognised by Young and Roper (1969) have been captured in the upper 200 m at night.

Diagnosis

Cycloteuthids are characterised by a subtriangular funnel locking cartilage, biserial toothed or smooth suckers on the arms and tetraserial suckers on the tentacular clubs. Buccal connectives attach to the ventral border of the ventral arms and light organs are present in adults, around the eyes, on the ventral mantle and at the arm bases in some species. Fins extend anteriorly for more than 70% of the mantle length in adults. In the genus Cycloteuthis, the mantle is elongate posteriorly, forming a distinct tail, and the ink sac bears a single light organ. In Discoteuthis, a tail is lacking, fins are very large and round and only mantle photophores are present. No mature cycloteuthid males have been described in the literature; the form or presence of hectocotylisation remains unknown.

General References

Clarke, M.R. 1980. Cephalopoda in the diet of sperm whales of the southern hemisphere and their bearing on sperm whale ecology. Discovery Reports 37: 1-324

Clarke, M.R. 1983. Cephalopod biomass — Estimation from predation. Memoirs of the National Museum of Victoria, Melbourne 44: 95-107

Clarke, M.R. & MacLeod, N. 1982. Cephalopod remains from the stomachs of sperm whales caught in the Tasman Sea. Memoirs of the National Museum of Victoria, Melbourne 43: 25-42

Lu, C.C. & Phillips, J.U. 1985. An annotated checklist of Cephalopoda from Australian waters. Occasional Papers of the Museum of Victoria 2: 21-36

Young, R.E. & Roper, C.F.E. 1969. A monograph of the Cephalopoda of the North Atlantic: the family Cycloteuthidae. Smithsonian Contributions to Zoology 5: 1-24

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