Gymnelus pseudosquamatus, Chernova & Møller, 2021

Chernova, N. V. & Møller, P. R., 2021, A new species of Gymnelus (Perciformes, Zoarcidae) from Greenland, similar to G. viridis, Proceedings of the Zoological Institute of the Russian Academy of Sciences 325 (1), pp. 34-48 : 42-46

Gymnelus pseudosquamatus sp. nov. – Deceptive Fish Doctor

( Figs 2B, D , 4 , 6–8 )

Gymnelus viridis (non Fabricius, 1780): Anderson 1982: 29 (part, fig. 16). – Chernova 1998: 163 (part: ZMUC P761126).

Holotype. ZMUC P764452 , male 142 mm TL, 138 mm SL, South-West Greenland, 64°38'N, 55°06'W, R/V “Paamiut”, st 14, 23 July 1998, 326 m depth; coll. P.R. MØller.

Paratypes, 57 specimens 54–172 mm TL from 12 stations. ZMUC P764453 (1), M 137 mm, caught with holotype . – ZMUC P765160 (1), M 120 mm, 72°05'N, 57°34'W, R/V “ Paamiut ”, st 3, 17 August 1997, 267 m depth ; coll. P.R. MØller. – ZMUC P765177 – P765185 (9), 121–156 mm, 66°01'N, 56°11'W, R/V “ Paamiut ”, st 22, 25 July 1998, 245 m depth; coll. P.R. MØller. – ZMUC P766368 (1), M 160 mm, Davis Strait, 68°22'N, 58°19'W, R/V “ Paamiut ”, 06 August 2003, 429– 457 m depth; coll. P.R. MØller. – ZMUC P766369 (1), M 114 mm, 67°26'N, 56°14'W, R/V “ Paamiut ”, st 34, 12 July 2003, 221 m depth ; coll. P.R. MØller. – ZMUC P2396102 – P2396110 (9), 2396113–122 (10), 2396124–129 (6), 108– 153 mm, “GrØnlands FiskeriundersØgelser”, PA 0200 37. – ZMH 8432 (6), MM (5) 114.5–146 mm and F 114 mm, 60°14.10'N, 47°39.20'W, R/V “ Walter Herwig ”, st 698/94, 25 October 1994, 240– 242 m depth; coll. M. Stehmann. – ZMH 8436 (2), FF 109 and 116 mm, 61°00.20'N, 49°29.80'W, R/V “Walter Herwig”, st 709/94, 27 October 1994, 142 m depth; coll. M. Stehmann. – ZMH 8437 (4), MM (2) 120 and 134 mm, FF (2) 111 and 113 mm, 61°21.80'N, 50°05.50'W, R/V “ Walter Herwig ”, st 711/94, 27 October 1994, 127– 151 m depth; coll. M. Stehmann. – ZMH 8438 (15), MM (6) 106–146 mm, FF (5) 97–120 mm and 4 juv 70–99 mm, 61°36.70'N, 50°17.10'W, R/V “Walter Herwig”, st 714/94, 28 October 1994, 130– 142 m; coll. M. Stehmann. – ZMH 8484 (5), M 145 mm and FF (4) 105–145 mm, 66°39.80'N, 54°57.40'W, R/V “ Walter Herwig ”, st 777/1994, 8 November 1994, 89–90 m depth, coll. M. Stehmann. – ZMH 25459 (4), MM (2) 172 and 164 mm, 2 juv 105 and 86 mm, 59°51.9'N, 43°10.5'W, R/V “ Walter Herwig ”, st 832/1993, 3 October 1993, 165– 168 m depth; coll. M. Stehmann. – ZIN 56451 (3), MM 102–132 mm, 61°02'N, 49°29'W, R/V “Walter Herwig III”, st 1062, 03 November 2001, 118– 152 m depth; coll. N.V. Chernova. – ZIN 56452 (1), M 98 mm, 63°01.39'N, 52°13.93'W, R/V “ Walter Herwig III”, cruise 233, st 1091, 06 November 2001, 239– 253 m depth; coll. N.V. Chernova. – ZIN 56504 (4, from ZMH 8438 ): M 159 mm, F 126 mm, 2 juv 54 and 85 mm, 61°36.70'N, 50°17.10'W, R/V “Walter Herwig”, st 714/1994, 28.10.1994, 130– 142 m depth; coll. M. Stehmann.

Additional materials: 9 specimens from 6 stations, 94–164 mm TL. ZMUC P765172 (1), F 158 mm, 66°31'N, 54°40'W, R/V “ Paamiut ”, st 4, 21 August 1998, 167 m depth; coll. P.R. MØller. – ZMUC P764454 (1), 108 mm, Baffin Bay, 72°03'N, 57°55'W, R/V “Paamiut”, st 36, 23 August 1998, 231 m depth ; coll. P.R. MØller. – ZMUC P765156 - P765158 (1, 1, 1), MM 124-164 mm, 60°56'N, 48°52'W, R/V “Paamiut”, st 27, 12 September 1998, 221 m depth; coll. P.R. MØller. – ZMUC P765159 (1), M 111 mm, 64°23'N, 54°20'W, R/V “ Paamiut ”, st 12, 23 July 1998, 218 m depth ; coll. P.R. MØller. – ZMUC P766753 – P766754 (2), MM 94 and 96 mm, 61°34'N, 50°13'W, R/V “ Paamiut ”, st 30, 27 July 2009, 171 m depth ; coll. P.R. MØller. – ZMUC P2396752 (1), M 111 mm, 70.88°N, 44[54]. 26°W [= 70°52'48"N, 54°15'36"W], “Kap Farvel”, Sigsby trawl, 29 September 1985, 95–180 m depth, Project 06419, AG 90034. – ZIN 56453 (1), F 99 mm, 62°41.15'N, 51°40.05'W, R/V “ Walter Herwig III”, cruise 233, st 1086, 06 November 2001, 227– 239 m depth; coll. N.V. Chernova.

Etymology. The species name “pseudosquamatus ” (Latin squāmātus = scaly) is given due to the presence of small light specks in the color, which can easily be mistaken for scales.

Diagnosis. Species of Gymnelus with supratemporal pores 2 (1+0+1). Dorsal fin begins above middle of pectoral fin; predorsal length 18.8–23.6 (on average 20.8)% TL. Trunk compressed in cross section. Dorsal-fin rays evenly lengthened (no group of short rays in front); fin membrane thin anteriorly. Eye not less than snout length; gill slit does not exceed eye diameter. Head on average 16.0% TL. Pectoral fin slightly longer than half of head length (on average 51.3% HL); pectoral fin base averages 36.6% of fin length. Vertebrae 94–101 (on average 97.6), D 90–98 (92.9), A 76–82 (78.8). Color with 8–16 wide dark-brown mottled bands; skin with small light speckles giving illusion of false tiny scales ( Fig. 7B ). Length up to 172 mm TL.

Description

The holotype is an adult male 142 mm TL ( Fig. 7A, D, E ). The maximum body depth is 10.5 times in TL and exceeds one-half of the head (56% HL). The trunk is compressed; at the base of the pectoral-fin, the depth-to-width ratio is 1.4 and 1.6 at the origin of the anal fin. The dorsal fin begins above the middle of the pectoral fin; predorsal length is 1.3 times of the head length. The anterior D -fin rays gradually and evenly lengthen and are covered with a thin fin membrane (rays are visible through it). The height of the D and A fins is less than 1/3 of the body depth. The pectoral fin has a narrow base (equal to 37% of the fin length), located obliquely under the opercular lobe.

The head is 5.9 times in TL, its width is equal to the head depth (both 50.0% HL). The eye is 4.3 in HL and is not less than the snout length. The nostrils are shorter than the pupil diameter. The mouth is terminal. The teeth are large and stout, of uneven size; they form 2–3 rows at the jaw symphysis, but are uniserial behind. There are 27 (17/4/6) teeth on the upper jaw, 19 (16/3) on the lower jaw, 7 on the vomer and 7 on the palatines. Respiratory membranes on the upper and lower jaws are wide; the one on the upper jaw almost reaches the teeth on the vomer. The gill slit is as long as the eye diameter and reaches down to the level of one-half of the P -fin base. The opercular flap is rounded; on the body under it there is a thin skin fold, closing tightly the gill opening. The sensory system has an interrupted supratemporal commissure; there are 2 supratemporal pores (1+0+1). Other pores: there are 2 nasal, 6 infraorbital, 8 preoperculo-mandibular, and 4 temporal (1+3) pores. The lateral line is mid-lateral and is indistinct at the posterior half of the tail. There is a row of rear neuromasts under the base of the anterior part of the dorsal fin.

Color in alcohol includes 12 broad dark-brown patterned bands separated by lighter intervals. The skin is mottled with tiny light specks, creating the illusion of small scales. This character is unique among all Gymnelus species. The belly, the underside of the head, and the pectoral fins are pale. The mouth and peritoneum are not pigmented. The anal fin is blackish as in the males of other Gymnelus species.

Variability. Paratypes are similar to the holotype in basic characters and measurements, including proportions ( Tables 1, 2). Body depth is uniform along the entire length (on average, 49% HL at the occiput, 50% above the P -fin and 49% above the A -fin beginning). The trunk is compressed; the depth-to-width ratio is 1.3 above the P -fin base and 1.6 above the A - fin origin. The dorsal fin begins above the middle of the pectoral fin; anterior rays lengthen gradually; the fin membrane is transparent, emarginating at the tips of the rays. SL = 0.965 TL.

The eye is about equal to the snout or slightly larger. The gill slit is not longer than the eye, reaching usually to the level of the upper third of the P -fin base. The cheek muscles in mature males are better developed than in females ( Figs 7E and G ), but insignificantly compared to other Gymnelus . The supratemporal commissura is interrupted (n=25), there are always 2 supratemporal pores (1+0+1); others pores: there are 2 nasal, 6 infraorbital (7 in one specimen), 4 temporal (1+3), and 8 preoperculo-mandibular pores.

Radiographs. D 90 – 98, A 76 – 82. D +1/2 C 95 – 101, A +1/2 C 81 – 87. Vertebrae 94 – 101: abdominal 17 – 20 and caudal 75 – 82. Vertebrae without ribs 2 – 3. Dorsal rays in precaudal part 15 – 17. First D -fin ray inserted between processes of 4/5 to 6/7 vertebrae; rayless pterygiophores in front 1 to 3 (rarely absent). Anterior dorsal-fin rays increase uniformly in length ( Fig. 2B, D ). Anal-fin rays before first haemal spine 2 – 4 (usually 3). Caudal fin with 9 – 13 rays, including 7 – 9 (usually 8) primary rays on hypurals, 1 – 2 upper and 1 – 2 lower secondary rays.

The specimen collected at the maximum depth of 429 – 457 m (male 160 mm TL, ZMUC P766368) does not differ from fishes caught in shallower waters (100 – 300 m) in main characters and proportions. The difference is in the main color, which is almost completely gray, including the head underside, lips and belly; but the upper part of the body is densely speckled with fine pale spots (false scales).

Allometry. In young individuals, the eyes are larger than in the adults and are usually bulging and protruding laterally. Compared to mature individuals, the upper jaw of young males (<137 mm TL) is shorter and does not extend behind the eye. The gill slit reaches the middle of the P -fin base (to the 5 – 6th rays).

Sexual dimorphism . Like other Gymnelus , males have slightly larger and broader head than females ( Fig. 7E, G ), with a longer upper jaw. In adult males the cheek muscles are enlarged ( Fig. 7D, F ). Like in other Gymnelus , the anal fin in females is pale and in males is blackish along the edge (even if they are immature). The ocelli on the dorsal fin ( Fig. 7B ) are more common in males.

Color. The number of dark brown stripes varies from 8 to 16, they become indistinct towards the end of the tail, especially in larger individuals. Scalelike speckles are always present on the nape, the upper side of the body and the dorsal fin. In males, the bands are rather uniform, in some specimens indistinct. In females (92–111 mm TL and more), the bands are usually bright and contrasting, chocolate brown with mesh spots; leopard patterns are present in some individuals. In larger females (158 mm TL) the banding is less distinct, the upper side of the head and body becomes more uniformly brown, but the nape and back are also dotted with small specks. The underside of the head and lips are pale. The ocelli (one to six, sometimes touching each other) may be present on the dorsal fin, usually in front, rarely in the middle, or even behind. The peritoneum, mouth and gill cavities are pale. The smallest fishes have a juvenile coloration consisting of 18 narrow vertical stripes on the body ( Fig. 8 ).

Size. Among congeners, G. pseudosquamatus is a medium-sized species. Males reach a total length of 172 mm, females 158 mm.

Distribution. The specimens have been caught at the outer shelf of the South-West Greenland ( Fig. 4 ). The southernmost record is at Kap Farvel (59°46'N, 43°55'W); the most northern and western are in the Baffin Bay (at 72°05'N, 57°34'W and 68°22'N, 58°19'W). The species occurs at a depth of 85 to 457 m; 76% of recordings were made below 100 m.

Biology. Females with a length of 125 mm TL, caught in August (ZMUC P765171) and in November (ZMH 8438), have maturing eggs in the ovaries with a diameter of about 4 and 3 mm. Spawning probably occurs in autumn, as the female 144 mm TL caught in November (ZMH 8438), had an egg size of 5 mm. It is obvious that it takes more than a year for an egg to develop.

Comparisons. Differences between the new species and G. viridis are shown above. Gymnelus pseudosquamatus differs from the second Greenland species, G. retrodorsalis , in the more anterior position of the dorsal fin (starting above the pectoral fin vs. almost above the beginning of the anal fin).

In the Eastern North Atlantic and adjacent Arctic, there are three other Gymnelus , which belong to the “two-pore” group: G. esipovi , G. knipowitschi and G. taeniatus . The new species differs from G. knipowitschi and G. taeniatus in the number of vertebrae (94–101 vs. 86–94), rays of the dorsal fin (90–98 vs. 86–92), in the position of the first dorsal-fin ray ( Fig. 5A, C ) and other characters ( Chernova 1999a). Gymnelus pseudosquamatus differs from G. esipovi in the lesser reduction of the anterior dorsal fin elements (the number of free dorsal-fin pterygiophores is 0–3 vs. 3–5 ( Fig. 5B ); the first dorsal-fin ray is inserted between the vertebrae from ¾ to 6/7 vs. 5/6 – 8/9; the predorsal length is 18.8–23.6% TL vs. 24.8–30.8%); also in color, maximum size ( G. esipovi does not exceed 132 mm TL) and other characters ( Chernova 1999b).

Figures

Fig. 2. Radiographs of Gymnelus: A, C – G. viridis, male 196 mm TL (ZIN 1945, one of the Reinhardt’s specimens); B, D – G. pseudosquamatus, male 108 mm TL (ZMUC P2396127, paratype). Arrows indicate four anterior shortened rays of the dorsal fin.

Fig. 4. Distribution of Gymnelus viridis (triangular marks) and G. pseudosquamatus, holotype (solid circle) and other materials (empty circles).

Fig. 6. Gymnelus pseudosquamatus: A – male 155 mm TL and B – female 122 mm TL (paratypes ZMH 8438).

Fig. 7. Gymnelus pseudosquamatus: A, D and E – male 142 mm TL (holotype ZMUC P 764452); C, F and G – female 126 mm TL (paratype ZMUC 765177); B – tiny pale speckles on the skin, giving the illusion of scales (paratype ZMH 25459, 164 mm TL).

Fig. 8. Gymnelus pseudosquamatus, banded color of juveniles, 105 and 86 mm TL (ZMH 25459).

Fig. 5. Radiographs of Gymnelus: A – G. knipowitschi, holotype; B – G. esipovi, holotype, C – G. taeniatus, holotype. Arrows indicate the first free pterygiophore and the first ray of the dorsal fin.