“Gonatus antarcticus LÖNNBERG, 1898
(Figs. 3A–B, 4A–J)
Gonatus species: STEENSTRUP, 1882, p. 150.
Gonatus antarcticus LÖNNBERG, 1898, p. 51-55, pl. v.
Gonatus antarcticus: CLARKE, 1980, p. 138-142, text-fig. 103.
Material examined: NSMT Mo-63957, Lat. 47º24'S, Long. 59°37'W, north of Forkland Islands in the South Atlantic Ocean, bottom trawl at about 928 m depth, “BANSHU-M ARU”, Japan Marine Fishery Resource Research Center (October 13, 1984). Deposited in National Science Museum, Tokyo.
Specimen deposited in the U.S. National Museum of Natural History, Smithsonian Institution, Lat. 40º18'S, Long. 35°07'W, South Atlantic Ocean (September 3, 1971).
Specimen deposited in Zoological Museum, Copenhagen, SAM A6514, locality unknown, date unknown. See measurements for size (Table 3).
Diagnosis: A gonatid with slender body (MW/DML= 18%), short arms (AL/DML =45%) and sagittate fins (FW/FL= 84%). Suckers in outer rows of Arms I, II, III are ⅔ smaller in size than those of Arm IV. Tentacular manus with a large central hook, a medium-sized distal hook and 3-4 small proximal hooks remarkably decreasing in size proximally.
Description: Mantle is slender, cylindrical in the anterior half, but gently tapering posteriorly to the blunt end of gladius cone from which a long gelatinous tail continues to the posterior end of the fin. Mantle wall is moderately thick and muscular but soft to touch. Ventral excavation is shallow (Fig. 3A).
Body is covered with a thin epidermis densely spotted with purplish chromatophores on ventral and aboral surfaces but epidermis is easily torn off by handling.
Fins are sagittate with roundish sides. Fin length is about half of the DML, FW/FL being about 84%. Posterior margins are slightly concave, but anterior margins are convex with small lobe to the fin base.
Head is squarish, slightly narrower than the mantle opening. Eyes are large, occupying almost entire lateral sides of the head with distinct sinus on the orbit. Neck is moderately constricted with two pairs of olfactory crests, one situated near the funnel groove and the other on dorso-lateral sides.
Funnel is moderate in size, reaching the posterior level of the eye lenses with smooth funnel groove. Funnel cartilages are lanceolate with rounded ends, about 9.5% of DML. Median groove is almost straight, widened anteriorly (Fig. 4J). Mantle locking cartilages are linear ridges, nearly of the same length as the corresponding funnel cartilages. Funnel organs are not observed.
Nuchal cartilage is rectangular with rounded ends, about 10% of DML in length, 3% of DML in width. Three straight grooves run along the longitudinal axis of the cartilage.
Arms are short, 40-45% of DML, stout proximally and tapering to the distal tips. Arm formula is IV, II=III, I, but the difference in length is not prominent. Arm IV has a thin lateral keel. Right Arm III of NSMT Mo-63957 shows regeneration of injured arm tip.
Arm armature is quadriserial. Median two rows of Arms I, II, III consist of hooks, arranged in a zigzag row. Marginal rows consist of small suckers arranged likewise. Hooks are covered with fleshy hood, connnected to the oral surface of the arm by short pedicel. Marginal suckers are situated at the distal end of long trabecula which supports a thin protective membrane along the margins of oral surface of the arms (Fig. 4I). Median two rows of Arm IV are not modified into hooks and this arm has quadriserial suckers throughout. The median and marginal suckers of Arm IV are nearly the same in size. Marginal suckers of Arms I, II and III are smaller, about ⅔ of the suckers of Arm IV. Both hooks and suckers decrease in size distally. Armatures in a proximal half length of the arms vary from 20 suckers plus 17 hooks in Arm I to 24 suckers plus 20 hooks each in Arms II and III. That of Arm IV is 44-46 suckers. Marginal suckers at the middle portion of Arms I, II and III have 6-9 pointed teeth on the distal margin of chitinous rings with smooth proximal margin (Fig. 4A-C). Chitinous rings of both marginal and median suckers of Arm IV have 7-8 pointed teeth (Fig. 4D-E).
Tentacles are long, stout and as long as DML, with medium-sized tentacular club. Tentacular stalk is nearly rectangular in cross section.
Tentacular club is about 15% of DML, having a large hook at the central portion of manus with a small hook, about ⅓ of the largest one, distal to it. Proximal to the large central hook, 3-4 much smaller hooks and/or suckers continue longitudinally, with a remarkable decrease in size proximally. Manus formula HHhhhh or HHhhhs or HHhhss. Dactylus has a well-defined dorso-aboral keel (Fig. 3B). Suckers on dactylus are about 150-160 in number, 4-5 rows densely beset, terminating in a circle at the tip. Suckers on dactylus have 4-5 rounded teeth on the distal margin of the chitinous ring (Fig. 4G). Suckers on dorso-marginal zone of manus are about 50-60 in number, continuing to the inner carpal group. Suckers on dorso-marginal zone have 6-7 blunt teeth (Fig. 4F). Ventro-marginal zone of manus consists of 14-15 trabeculae connected with a thin membrane, each of them bears 3-4 suckers, continuing to the ventral marginal suckers of tentacular stalk in a single row. Ventro-marginal suckers have 7 blunt teeth (Fig. 4H). Carpal group consists of 5-6 large, smooth-ringed suckers set alternately on a thick ridge with fleshy knobs. Proximal to the carpal group, a series of alternating small, smooth-ringed suckers and pads continues almost in entire length of oral-dorsal margin of the tentacular stalk. Between ventral and dorsal marginal suckers of tentacular stalk, about 120-140 small suckers are scattered near the base of stalk.
Table 3. Measurements of Gonatus antarcticus LÖNNBERG, 1898 in mm.
Characters
NSMT Mo-63957
Specimen in USNM
Specimen in Zool. Mus. Copen.
Sex
-
-
female
DML
230
235
218
Tail L
50
52
54
MW
40
42
44
FL
114
103
101
FW
95
84
89
FBL
100
-
-
HL
28
35
33
HW
32
28
35
ED
22
-
24
NCL
23
-
22
NCW
7
-
8.5
FCL
22
-
21
FCW
5.8
-
7.0
AL
right
I
90
103
74*
II
92
110
110
III
70**
113
105
IV
104
104
108
left
I
88
-
91
II
91
-
115
III
91
-
114
IV
102
-
110
1/2AAC
right
I
20s/1s+17h
22s/19h
-
II
22s/1s+19h
24s/2s+21h
-
III
18s/13h**
22s/2s+20h
-
IV
44s
50s
-
left
I
18s/1s+17h
-
21s/2s+20h
II
24s/1s+20h
-
22s/2s+20h
III
22s/1s+21h
-
21s/2s+21h
IV
46s
-
50s
TL
right
240
280
150
left
238
-
145
TCL
right
35
33
35
left
34
-
34.8
DSC
150-160
160-170
-
DMSC
50-60
70-80
-
VMSC
50-60
55-65
-
TCAF
HHhhhs
HHhhss
HHhhhh
DML, dorsal mantle length; Tail L, tail length; MW, mantle width; FL, fin length; FW, fin width; FBL, fin base length; HL, head length; HW, head width; ED, eye diameter; NCL, nuchal cartilage length; NCW, nuchal cartilage width; FCL, funnel cartilage length; FCW, funnel cartilage width; AL, arm length; l/2AAC, proximal half length of arm armatures count, expressed marginal suckers/midian suckers+hooks; TL, tentacle length; TCL, tentacular club length; DSC, dactylus sucker count; DMSC, dorso-marginal sucker count; VMSC, ventro-marginal sucker count; TCAF, Tentacular club armatures formula expressed in the number of hooks or suckers from distal to proximal with symbols H indicating the distal large hook, H, the central large hook, h, the proximal small hook and s, the proximal small sucker. * arm tip lacking; **regenerated arm.
Buccal membrane has 7 lappets, connected to the dorsal borders of Arms I and II, and to the ventral borders of Arms III and IV, being of DDVV-type. Outer lip is thin, darkly pigmented. Inner lip is thick, muscular with numerous small fleshy warts.
Beaks, radula, gladius and viseral organs were not observed because of scarcity of available specimens.
Discussion: Among the known Gonatus species, G. antarcticus is considered to be closely related to G. fabricii - G. steenstrupi complex in the North Atlantic and G. californiensis in the Northeast Pacific (KRISTENSEN, 1981; YOUNG, 1972). According to LÖNNBERG (1898), G. antarcticus has greatly reduced marginal suckers and compressed hooks on Arms I–III. The relative smallness of marginal suckers of Arms I–III in comparison with that of Arm IV was recognized in the present specimen. However, the expression of "greatly reduced" seemed to be somewhat exaggerated. In the recent systematic study of Atlantic Gonatus, KRISTENSEN (1981) pointed out that G. antarcticus has very strong tentacles with numerous (118-190) small suckers on the median portion of the tentacular stalk and rather small clubs with more numerous suckers (270) than in any other Gonatus species. These characters were confirmed in the present study. KUBODERA and OKUTANI (1981) calculated some bodily proportions of seven Gonatus species. From their table, it is clear that G. antarcticus has comparatively narrower fins than other Gonatus species. IMBER (1978) considered that G. californiensis is synonymous with G. antarcticus and suggested that the ranges of the two populations are almost certainly confluent via the eastern central Pacific. However, G. californiensis is clearly distinguishable from G. antarcticus by the characters mentioned above.
The present study revealed that the arrangement of hooks on the proximal portion of the central large hook of manus apparently separates G. antarcticus from others. G. antarcticus has 3-4 hooks proximal to the central large hook among which the most distal one is the largest and decreasing rapidly in size proximally. Such a serial decrease in size of the hooks distal to the central large hook has never been seen in other Gonatus species in the Northern Hemisphere. This character is equally observed in three specimens examined and considered to be one of the important specific characters of G. antarcticus.”
(Kubodera & Okutani, 1986: 135-140)
Gonatus antarcticus is a squid in the family Gonatidae. The species is known with certainty only from southern Atlantic waters but it may have a circum-Antarctic distribution.[3][4]
G. antarcticus occurs in waters of the Southern Ocean. Its range may be circumpolar with an Antarctic and Sub-Antarctic distribution.[5][4]
This squid is eaten by several predators in the Southern Ocean, like Albatrosses, Sperm whales, Seals and Penguins.
Based on stable isotopes analysis, this squid may be a top predator on its natural habitat.[5][6]
Gonatus antarcticus is a squid in the family Gonatidae. The species is known with certainty only from southern Atlantic waters but it may have a circum-Antarctic distribution.
