FAO Species Identification Guide for Fishery Purposes Western

784 Cephalopods
Onychoteuthidae ONYCHOTEUTHIDAE
Hooked squids
by M.C. Dunning
Diagnostic characters: Medium-sized to large oceanic squids,
with a strong, muscular torpedo-shaped mantle and large
muscular rhomboidal fins attenuated posteriorly in some species.
Funnel locking cartilage simple, straight. Buccal connectives
attached to ventral border of ventral arms. Arms with
biserial and sometimes smooth suckers; tentacular clubs with
biserial medial hooks and 2 rows of marginal suckers in the
immature stages. Club-fixing apparatus consisting of smoothringed
suckers and corresponding knobs present at the base of the
tentacular clubs. Hectocotylisation not evident in males. Numerous
distinctive pleats or folds are present in the neck region in Onychoteuthis
and Ancistoteuthis (see Fig. 2a), and the skin of Moroteuthis
often contains subcutaneous papillae and ridges. Lateral
arms have swimming keels in some of the larger species. Visceral
light organs are present in the genus Onychoteuthis.
Habitat, biology, and fisheries: Onychoteuthids occur in tropical
to polar waters in all oceans. They are oceanic squid, occasionally
encountered in continental slope waters where they may be caught
in demersal trawls. They feed on a broad range of fish, crustaceans
including krill, squid, and other pelagic molluscs, and are at least
partially cannibalistic. Known predators include lancetfish, tunas,
whales, dolphins, seals, and albatrosses. Onychoteuthids form
schools. Juvenile Onychoteuthis are able to leap above the surface
to escape predators, as do ommastrephids, and sometimes are
found on the decks of vessels. Immature Moroteuthis species
share with other epipelagic cephalopods the deep blue dorsal day
coloration characteristic of the neuston generally. Onychoteuthids
are not fished commercially in the Western Central Pacific, although
sometimes Moroteuthis are caught incidentally in demersal
trawls in continental slope waters (300 to 600 m) off northern
Australia and in the South China Sea.
Remarks: Recent taxonomic studies have indicated that at least
some tropical oceanic onychoteuthids previously assigned to the
genus Onykia may be juveniles of various species of Moroteuthis.
Similar families occurring in the area
Ommastrephidae: also with an arrow-shaped fin, but can be
distinguished by the following characters: funnel-mantle locking
apparatus ⊥-shaped; sucker rings toothed; no hooks on tentacular
clubs; buccal connectives attached to dorsal border (rather
than to ventral border) of ventral arms.
4 rows of
suckers,
no hooks
tentacular club
Ommastrephidae
dorsal view
2 rows of
hooks
tentacular club
Onychoteuthidae