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Tentacle Morphology of the Giant Squid <I BULLETIN OF MARINE SCIENCE, 71(2): 725–737, 2002 TENTACLE MORPHOLOGY OF THE GIANT SQUID ARCHITEUTHIS FROM THE NORTH ATLANTIC AND PACIFIC OCEANS Martina A. C. Roeleveld ABSTRACT 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 approxi- mately equal numbers. The smooth-ringed suckers and the knobs extend in pairs proxi- mally 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 suck- ers 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 appa- ratus 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 in- creases 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 num- ber of suckers, though variation is wide in both oceans. Architeuthis is one of the most morphologically variable squids (Förch, 1998; Roeleveld, 2000) and measured tentacle lengths range from 23% to 832% mantle length (ML) (Tsuchiya and Mori, 1998; Kirk, 1888). It is therefore surprising to find that the relative dimensions of the tentacles, and the number of tentacular suckers, show some correlation among themselves and with ML. Club morphology has been found to be of systematic significance in other squid families such as the Loliginidae and Ommastrephidae (Nesis, 1987; Roeleveld, 1982). This study compares tentacle data from North Atlantic and North and South Pacific Architeuthis for the first time. The accumulation of sufficient data to plot meaningful graphs is also rather rare for Architeuthis. This study arose from the need to reconstruct Architeuthis tentacles for a model on exhibition at the South African Museum. All 15 Architeuthis specimens in the South African Museum lack tentacles and the tentacular morphology of South African Architeuthis remains unknown. 725 726 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002 MATERIAL AND METHODS Listed in Table 1 are locality, repository and specimen data for the Architeuthis tentacles studied. The specimen reference numbers were allocated sequentially when the specimens were first exam- ined and facilitate identification of individual specimens that may have the same catalogue number, or none. ABBREVIATIONS AND DEFINITIONS: Club suckers — total number of suckers on the manus + dactylus + carpus + fixing apparatus FXA — fixing apparatus of alternating knobs and smooth-ringed suckers in transverse rows of more than two suckers or knobs Maturity stages — after Roeleveld and Lipiƒski, 1991: stage I — immature; stage II — matur- ing; stage III — mature ML — mantle length (mm) Sucker diameter — size of largest sucker on the manus (mm) Tentacle suckers — total number of suckers on the club + stalk TL — tentacle length (mm) RESULTS The Architeuthis tentacle consists of a club and a stalk. Most of the tentacular stalk bears alternating suckers and knobs, more or less in pairs, but a short proximal part of the stalk is bare. The club consists of four distinct regions, the (distal-most) dactylus, manus, carpus and (proximal) fixing apparatus. Suckers on the dactylus are arranged in oblique quadriserial rows and decrease in size from ventral to dorsal (Fig. 1). The manus suckers are also obliquely quadriserial but the two middle suckers of each row are larger than the lateral suckers (Fig. 2). Proximal to the manus a triangular region has irregularly ar- ranged suckers, and quadriserial rows do not occur (Fig. 3). The suckers of the dactylus, manus and carpus have toothed inner rings, in contrast to the smooth inner rings of the suckers of the fixing apparatus. The fixing apparatus con- sists of a distinct cluster of alternating suckers and knobs in approximately equal num- bers with no clear arrangement in rows (Fig. 3). Distally on the fixing apparatus about six suckers occur across the oral surface of the club; alternating suckers and knobs, remain- ing about the same size, become progressively fewer in number transversely and more widely spaced proximally, and extend along the tentacular stalk for 12–73% of the ten- tacle length. The knobs alternate fairly regularly with the smooth-ringed suckers on both Figure 1. Dactylus sucker arrangement, left club, ventral side uppermost, Architeuthis, NA-20, M III 1180, no locality data, Science Museum, Trondheim. D1 - D30, dactylus rows 1 - 30. M14, manus row 14. 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