Tentacle morphology of the giant squid Architeuthis from the North Atlantic and Pacific oceans

The tentacles of Architeuthis are very variable in length, from 0.2 to eight times mantle length (ML), and they increase in length with growth in ML. The tentacular clubs also increase in length with growth but not as fast as the whole tentacle. The Architeuthis club is unique in having both a triangular carpus with irregularly arranged toothed suckers and a fixing apparatus consisting of a cluster of smooth-ringed suckers and knobs in approximately equal numbers. The smooth-ringed suckers and the knobs extend in pairs proximally along the tentacular stalk for some 12–70% of the tentacle length. The proximal 14–28% of the tentacular stalk is devoid of suckers and knobs. The total number of suckers on the Architeuthis tentacle is remarkably constant during growth for so large and variable an animal. The manus and dactylus suckers do not appear to increase in number with ML but the lengths of these two club regions do increase, indicating growth in sucker size. The toothed carpal suckers and the smooth-ringed suckers of the fixing apparatus increase in number with growth, while the number of smooth-ringed suckers on the tentacular stalk remains the same. The length of the sucker-bearing tentacular stalk increases markedly with total tentacle length and ML, indicating increasingly widely spaced pairs of suckers and knobs. The relatively constant number of tentacular club and stalk suckers suggests that these suckers are of more than usual importance for the squids throughout ontogeny, probably mainly in feeding. The extensive locking apparatus of the carpus, fixing apparatus and stalk suggests that the two tentacles are held together to catch targeted prey, as has been observed in other squids. Stomach contents recorded for Architeuthis thus far are both demersal and pelagic in origin and include fast-swimming fishes and squids. Preliminary comparison of tentacle data from North Atlantic and North and South Pacific specimens showed some differences in relative dimensions and number of suckers, though variation is wide in both oceans.