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. ROELEVELD: TENTACLE MORPHOLOGY OF ARCHITEUTHIS 727
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S 728 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002
Figure 2. Manus sucker arrangement, left club, ventral side uppermost, Architeuthis, NZ-16, F ?II 2000. A - A, border between manus and dactylus; B - B, border between manus and carpus; note that two carpal suckers lie over this line, though their stalks are seated proximal to it; M1 - M14, manus rows 1 - 14; three suckers of manus row 4 are missing; the horizontal line indicates the extent of the manus. the fixing apparatus and tentacular stalk. The proximal 11–28% of the tentacular stalk is devoid of suckers and knobs. As a point of reference, the division between fixing appara- tus and tentacular stalk is defined as the point proximal to which no more than two suck- ers occur in an oblique line across the oral surface (as in Förch, 1998). Club length is also measured from this point. Tentacle length, including both club and stalk, is highly variable (minimum, mean and maximum of 143-387-493% ML in this sample; Table 2). Nevertheless, there is a trend to proportional increase of tentacle length with growth in ML from 56–2020 mm, n = 23 (Fig. 4). Club length increases with ML (38-54-80% ML, 12-14-18% TL, Fig. 5) but the variation and rate of increase are considerably less than that of the whole tentacle (club plus stalk, Fig. 4), indicating that the stalk is the fastest growing part of the tentacle. The length of the sucker-bearing part of the stalk (12-62-73% TL) increases markedly with tentacle length and ML (Fig. 6), indicating increasingly widely-spaced suckers (and knobs), since the number of suckers remains about the same (see below), whereas the length increase of the shorter, proximal part of the stalk, devoid of suckers and knobs, (11-18- 28% TL) is much less marked. On the club itself, the lengths of the manus and dactylus increase with growth, indicat- ing increase in sucker size, since the number of suckers remains the same (see below). In this sample the largest manus suckers are 1–33 mm in diameter (range and mean 1.4-1.7- 2.2% ML, Fig. 7) and diameter increases somewhat with growth in ML. The manus (5-8- 12% TL) grows faster than the dactylus (3-4-8% TL) and fixing apparatus plus carpus combined (2-4-6% TL; Figs. 8,9). The latter two regions were combined because the triangular shape of the carpal region is difficult to measure meaningfully.
Figure 3. Carpus and fixing apparatus sucker and knob arrangement, left club, ventral side uppermost, Architeuthis, NZ-16, F ?II 2000. C - C, border between fixing apparatus and tentacular stalk, also proximal boundary of club; the horizontal lines indicate the extent of the carpus and fixing apparatus. ROELEVELD: TENTACLE MORPHOLOGY OF ARCHITEUTHIS 729
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S 730 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002
Figure 4. The relationships between tentacle length and mantle length for Architeuthis from the North Atlantic and Pacific Oceans. The sucker counts for the different regions of the tentacular club and stalk are remark- ably consistent for so variable an animal (Figs. 10–12, Table 3). In 17 specimens ranging from 970–2020 mm ML the total number of tentacular suckers is 268–310 (mean 284, SD 13). The dactylus bears 112-127-156 suckers in quadriserial rows and the manus 48- 54-60 suckers. The manus and dactylus suckers do not appear to increase in number with ML (Fig. 11). The sucker counts are more variable in the wrist region (carpus plus fixing apparatus; Fig. 12); 15-24-44 toothed carpal suckers that increase in number with growth
Figure 5. The relationships between club length and mantle length for Architeuthis from the North Atlantic and Pacific Oceans. ROELEVELD: TENTACLE MORPHOLOGY OF ARCHITEUTHIS 731
Figure 6. The relationships between lengths of bare stalk and sucker-bearing stalk with tentacle length for Architeuthis from the North Atlantic and North and South Pacific Oceans. in ML. There is a clear difference in the number of smooth-ringed suckers on the fixing apparatus between the specimens from Atlantic (40-57-74) and Pacific (34-45-53) re- gions; within each geographical region this sucker count increases with ML (Fig. 12). The number of smooth-ringed stalk suckers (15-27-34) remains more or less the same (Fig. 11). A comparison of club morphometrics shows that the Pacific specimens have a rela- tively longer manus (Fig. 8), shorter carpus plus fixing apparatus (Fig. 9), fewer suckers
Figure 7. The relationships between maximum sucker diameter (SD-T) and lengths of mantle and club for Architeuthis from the North Atlantic and Pacific Oceans. 732 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002
Figure 8. The relationships between lengths of manus and dactylus with club length for Architeuthis from the North Atlantic and Pacific Oceans. in the fixing apparatus (Fig. 12), and possibly also larger manus suckers (Fig. 7). Re- gional differences in manus length vs club length, in sucker diameter relative to club length and in number of suckers in the fixing apparatus are not echoed in dactylus length, sucker diameter relative to ML, nor in number of carpal suckers.
Figure 9. The relationships between length of fixing apparatus plus carpus with club length for Architeuthis from the North Atlantic and Pacific Oceans. ROELEVELD: TENTACLE MORPHOLOGY OF ARCHITEUTHIS 733
Figure 10. The relationships between number of suckers on the club plus stalk with mantle length for Architeuthis from the North Atlantic and Pacific Oceans.
DISCUSSION
The quadriserial sucker arrangement of the manus and dactylus probably represents the plesiomorphic state for squids and is much like that of loliginids and ommastrephids. The triangular carpus with irregularly arranged suckers is unique to Architeuthis. Similar carpal sucker arrangements in more than four rows are found in the families Brachioteuthidae (Chun, 1910, pl. 31) and Neoteuthidae (Roper et al., 1969) but the suckers occur in much larger numbers and smaller sizes in those families. A proximal fixing apparatus forming a cluster of smooth-ringed suckers alternating with knobs is also found in Enoploteuthidae, Onychoteuthidae and some Cranchiidae (Roper et al., 1969). Suck- ers extending for a considerable distance along the tentacular stalk also occur in other families, e.g., in some gonatids (Young, 1972), thysanoteuthids (Roeleveld and Pheiffer, 1986) and cranchiids (Voss, 1980). The configuration in Architeuthidae of irregularly- arranged, toothed, carpal suckers and a fixing apparatus, starting as a cluster of smooth- ringed suckers and knobs, that then extends proximally along most of the tentacular stalk, is found in no other family of squids. The relatively constant number of tentacular club and stalk suckers in Architeuthis suggests that these suckers are of more than usual importance in squids, probably mainly during feeding. This is to be expected for control of tentacles that may attain 15 m in length (Kirk, 1888). The extensive locking apparatus of the carpus and stalk suggests that the two tentacles may be held together to catch targeted prey, in the manner recorded for other squids (Sthenoteuthis pteropus, Baker, 1957; Gonatus onyx, Hunt and Seibel, 2000). Species and genera recorded from Architeuthis stomachs thus far (Pérez-Gándaras and Guerra, 1978; Förch, 1998; Lordan et al., 1998) are both benthopelagic and demersal (the Norway lobster, Nephrops; the horned octopus, Eledone cirrhosa; macrourid fishes, Caelorinchus, possibly Kuronezumia (tentatively identified fish scales) and Lepidorhynchus; and possibly the orange roughy, Hoplostethus) and pelagic, including 734 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 2, 2002
Figure 11. The relationships between number of suckers on the manus, dactylus and stalk with mantle length for Architeuthis from the North Atlantic (NA) and Pacific (P) Oceans.
fast-swimming fishes and squids (a euphausiid; onychoteuthid, histioteuthid and ommastrephid squids; the horse mackerel, Trachurus, and the blue whiting, Micromesistius). It is difficult to distinguish between primary prey, taken by the giant squid itself, and secondary prey, probably from the stomachs of its prey items. Other items from the Architeuthis stomachs (the mussel, Modiolus, the pearlside fish, Maurolicus, ascidians, most of the nematodes and cestodes, and copepods) were probably secondary prey (Lordan et al., 1998; Nesis, pers. com.). Several other genera (including Trachurus,
Figure 12. The relationships between number of suckers on the fixing apparatus and carpus with mantle length for Architeuthis from the North Atlantic (NA) and Pacific (P) Oceans. ROELEVELD: TENTACLE MORPHOLOGY OF ARCHITEUTHIS 735
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Nephrops, Eledone and perhaps also Micromesistius) may have been caught and eaten incidentally in the trawls and were not primary prey of Architeuthis (Nesis, pers. com.). On the other hand, it could be argued that Architeuthis was feeding naturally on these species and consequently predator and prey were caught together in the trawls. The much-debated question, whether Architeuthis is an efficient swimmer or a slug- gish ambush predator, depends on the basis for comparison. Architeuthis seems lumber- ing in comparison with fast-swimming, streamlined ommastrephids. But it is probably no slower than other ammoniacal squids such as cranchiids, chiroteuthids or histioteuthids. Comparison of tentacle data from North Atlantic and Pacific specimens shows that while variation in lengths and sucker counts is wide in both regions and data for both seem to follow the same trends, there are regional differences in several of these charac- ters. Pacific specimens have a relatively longer manus, shorter carpus plus fixing appara- tus, fewer suckers in the fixing apparatus and possibly larger manus suckers. These dif- ferences are arguably the first indication of geographic variation. More data, to cover the wide variation and a greater geographic distribution, are necessary to determine if the differences are sufficiently great to justify recognition of more than one species or sub- species of Architeuthis worldwide. The small male described by Toll and Hess (1981) was clearly unique, being characterised by maturity at a very small size (ML 167 mm; Förch, 1998). It probably represents a distinct species and perhaps even a separate genus.
ACKNOWLEDGMENTS
I would like to thank K. Nesis (P.P. Shirshov Institute of Oceanology, Moscow), S. O’Shea (National Institute of Water and Atmospheric Research Ltd, Wellington, New Zealand) and C. Roper (National Museum of Natural History, Washington D.C.) for kindly bringing Architeuthis tentacles to Cape Town for the CIAC ’97 symposium and workshops. Thanks also to J. Knudsen, H. Petersen, E. Willasen, J.-A. Sneli and all the other friends and colleagues who helped with arrangements and actual examinations of giant squids in Copenhagen, Bergen, Trondheim and Cape Town; and to L. Compagno for assistance with Statistica© and information about fish prey species. This study was funded in part by the Foundation for Research Development and the South African Museum, Iziko Museums of Cape Town. The final version has benefitted considerably from the comments of K. N. Nesis and an anonymous referee.
LITERATURE CITED
Baker, A. d. C. 1957. Underwater photographs in the study of oceanic squid. Deep-Sea Res. 4 (2): 126–129. Brinkmann, A. 1916. Kjaempeblaekspruten (Architeuthis dux Stp.) i Bergens Museum. Naturen 1916: 175–182. Chun, C. 1910. Die Cephalopoden. 1. Teil: Oegopsida. Wiss. Ergebn. dt. Tiefsee-Exped. “Valdivia” 18: 1–401. Förch, E. C. 1998. The marine fauna of New Zealand: Cephalopoda: Oegopsida: Architeuthidae (giant squid). NIWA Biodiv. Mem. 110: 1–113. Grieg, J. A. 1933. Cephalopods from the west coast of Norway. Bergens Mus. Arb. 1933: 1–25. Hunt, J. C. and B. A. Seibel. 2000. Life History of Gonatus onyx (Cephalopoda: Teuthoidea): ontogenetic changes in habitat, behavior and physiology. Mar. Biol. 136: 543–552. Kirk, T. W. 1888. Brief description of a new species of large decapod (Architeuthis longimanus). Trans. Proc. N.Z. Inst. 20: 34–39. ROELEVELD: TENTACLE MORPHOLOGY OF ARCHITEUTHIS 737
Lordan, C., M. A. Collins and C. Perales-Raya. 1998. Observations on morphology, age and diet of three Architeuthis caught off the west coast of Ireland in 1995. J. Mar. Biol. Ass. U.K. 78: 903– 917. Nesis, K. N. 1987. Cephalopods of the world. T.F.H. Publications Inc., New Jersey. 351 p. ______, A. M. Amelekhina, A. R. Boltachev and G. A. Shevtsov. 1985. [Occurrence of giant squids of the genus Architeuthis in the North Pacific and South Atlantic.] Zool. Zh. 64: 518– 528. [in Russian with English abstract]. Pérez-Gándaras, G. and Á. Guerra. 1978. Nueva cita de Architeuthis (Cephalopoda:Teuthoidea): Descripcion y alimentacion. Investigacion Pesq. 42(2): 401–414. Roeleveld, M. A. C. 1982. Interpretation of tentacular club structure in Sthenoteuthis oualaniensis (Lesson, 1830) and Ommastrephes bartramii (Lesueur, 1821) (Cephalopoda, Ommastrephidae). Ann. S. Afr. Mus. 89: 249–264. ______. 2000. Giant squid beaks: implications for systematics. J. Mar. Biol. Ass. U.K. 80: 185–187. ______and M. R. Lipiƒski. 1991. The giant squid Architeuthis in southern African waters. J. Zool., Lond. 224(3): 431–477. ______and F. Pheiffer. 1987. The diamond squid. Sagittarius 2: 20–22. Roper, C. F. E., R. E. Young and G. L. Voss. 1969. An illustrated key to the families of the order Teuthoidea (Cephalopoda). Smithson. Contrib. Zool. 13: 1–32. Toll, R. B. and S. C. Hess. 1981. A small, mature male Architeuthis (Cephalopoda: Oegopsida) with remarks on maturation in the family. Proc. Biol. Soc. Wash. 94(3): 753–760. Tsuchiya, K. and K. Mori. 1998. A note on an early juvenile specimen of Architeuthis sp. collected from the south off central Honshu, Japan (Cephalopoda: Architeuthidae). Venus, Jap. J. Malacol. 57(3): 225–230. Voss, N. A. 1980. A generic revision of the Cranchiidae (Cephalopoda: Oegopsida). Bull. Mar. Sci. 30: 365–412. Young, R. E. 1972. The systematics and areal distribution of pelagic cephalopods from the seas off southern California. Smithson. Contrib. Zool. 97: 1–159.
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