Family ARCHITEUTHIDAE

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Family ARCHITEUTHIDAE

Giant Squids

Compiler and date details

2012 - Updated by Julian Finn, Museum Victoria, Carlton, Victoria, Australia

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

Introduction

The giant squid family Architeuthidae Pfeffer, 1900 is monogeneric; 21 nominal species have been described. All species are poorly defined and some workers have suggested that all specimens can be assigned to as few as three species (Roper & Boss 1982; Nesis 1982; Roper & Jereb 2010).

The first record of this family from Australian waters was of a stranded specimen from eastern Victoria, assigned by Allan (1948) to Architeuthis kirki C.W. Robson. A larval Architeuthis was caught in a midwater trawl in the upper 20 m off the central New South Wales coast in October, 1981 and a living juvenile female in this same region in the upper 300 m in January, 1982 (Lu 1986).

Individuals of Architeuthis species reach mantle lengths (ML) in excess of 4.5 m and weights of more than one tonne (Clarke 1966) and are the largest living cephalopods. Buoyancy is provided by a relatively high concentration of ammonium ions in the muscles of the mantle, head and arms (Clarke et al. 1979). The oxygen carrying capacity of the haemocyanin in the blood of Architeuthis is very low compared to that of other active oceanic squids such as ommastrephids (0.3 compared with 1.6 to 1.9 mM O2). This, coupled with the pronounced temperature sensitivity of its oxygen affinity, may limit the distribution of adult specimens to low water temperatures. Their encounters with warm currents may result in suffocation and hence explain the high correlation of strandings with warm water inflow in some areas (Brix 1983).

Size at maturity in male Architeuthis appears to be variable and perhaps represents differences between species. Specimens from 179 mm to in excess of 1000 mm ML have been found with apparently viable spermatophores (Toll & Hess 1981). The size at which females first reach maturity is uncertain. Female Architeuthis lack spermathecae. A recently captured female with ML 2.4 m was found have mated. Spermatophores were found embedded in the skin on both ventral arms. On one arm, the remains of several spermatophores up to 80 mm in length radiated under the skin from a single small entry point, about 10 mm in diameter; they did not penetrate the arm musculature. It is unclear how the spermatophores are inserted; the male may inject the spermatophores with the large muscular penis or use his beak to make the entry wound through which they are injected (Norman & Lu 1997). Mature eggs in Architeuthis reach 1.2–1.8 mm in length (Roeleveld & Lipinski 1991). Boyle (1986) estimated the potential fecunidity of a female at over 10 million eggs.

Examination of the blood chemistry of Architeuthis together with the lack of strong musculature in the funnel and fins, suggest that these animals are relatively poor swimmers and passive, sluggish predators (Roper & Boss 1982; Brix 1983). Architeuthis has been recorded from the diets of sperm whales and mako sharks in Australian waters (Clarke 1980; Dunning et al. 1993) and elsewhere from lancetfish, swordfish, albacore tuna and sperm whales (Clarke 1966; Roper & Young 1972; Toll & Hess 1981). Fish and cephalopods (including ommastrephids and histioteuthids) have been found among the stomach contents of the few specimens of Architeuthis examined (Pérez-Gándaras & Guerra 1978; Toll & Hess 1981; Roper & Boss 1982).

Data on numerical abundance of Architeuthis remains in individual sperm whale stomachs suggest that they may be solitary animals (Clarke 1980). The vertical distribution of adults is unclear. Clarke (1980) and Roper & Boss (1982) suggest that they may live on or near the bottom in depths of 1000 m or more. The capture of a larva in near-surface waters off eastern Australia may be an indication of ontogenetic descent (Lu 1986). Jackson et al. (1991) reported that the growth rings on the statolith of Architeuthis are similar in appearance to daily growth rings found in other squids studied; a juvenile female of 42.2 cm ML had 153 rings.

The distribution of Architeuthis in Australian waters remains unclear although all available records are from south of 32°.

Diagnosis

The genus Architeuthis Steenstrup is characterised by a muscular mantle, short oval fins and simple, straight, funnel locking cartilage. The buccal connectives attach to the dorsal border of arms IV. The arms have biserial suckers with many small sharp teeth. The proximal end of the tentacular club has a distinct cluster of small suckers and knobs, and larger quadriserial suckers distally. Two longitudinal rows of alternating suckers and pads are present along the tentacular stalks. Photophores are absent. The presence of hectocotylus in mature males is uncertain, as reports are contradictory.