ECOLOGY OF THE OCEANIC SQUID ONYCHOTEUTHIS BANKSI AND THE RELATIONSHIP BETWEEN THE GENERA ONYCHOTEUTHIS AND CHAUNOTEUTHIS (CEPHALOPODA, ONYCHOTEUTHIDAE)

Ontogenetic changes in the body morphology, morphometrics, age, growth , maturation, fecundity, feeding spectrum and parasites were studied i n 218 specimens of the oceanic nektonic squid Onychoteuthis banksi and in two specimens of the rare planktonic squid Chaunoteuthis mollis (O nychoteuthidae) caught in the tropical waters between 1977 and 1990. S imilarities between the two species in major taxonomic features and in several morphometrical indices suggest that C. mollis is in fact a ma ture female of O. banksi with degenerated mantle and fin muscles and l ost tentacles. Thus, C. mollis will be considered as a lesser synonym of O. banksi. Statolith microstructure analysis reveals that O. banksi is a slow-growing squid with low maturation rates, spending the first 240-260 d of Life in the epipelagic zone. The main features of the re productive strategy include earlier maturation of the males, small egg s (0.2-0.5 mm in diameter by the end of protoplasmic growth), synchron ous development of oocytes and high potential fecundity (51,000-205,00 0 eggs). Onychoteuthis banksi is an opportunistic predator, shifting t o a fish and squid diet much earlier and at smaller sizes (20-40 mm ML ) than ommastrephid squid. The feeding activity of small and medium O. banksi (20-80 mm ML) is a little higher and that of large O. banksi ( 80-148 mm ML) is lower than in ommastrephids of the same size. The hel minth fauna of O. banksi is impoverished and consists of 'food parasit es': larval Didymozoidea and Scolex spp. The level of infection is low , only reaching similar to 52 specimens per host in large squid. The n ature of the life cycle of O. banksi and possible evolutionary trends in the development of the 'Chaunoteuthis' stage for maturation and spa wning of females in the deep water are discussed.