Thorogobius alvheimi, Sauberer & Iwamoto & Ahnelt, 2018

Sauberer, Michael, Iwamoto, Tomio & Ahnelt, Harald, 2018, Two new deep-water species of the genus Thorogobius (Teleostei: Gobiidae) from the upper continental slope of the Eastern Central Atlantic, Zootaxa 4429 (2), pp. 357-371 : 360-366

Thorogobius alvheimi sp. nov.

( Figures 1–3 , 7 ; Tables 1–3)

Holotype. CAS 222482 , female, standard length+caudal fin length 72.1+ 19.8 mm; Angola, off Luanda (8°24′S, 12°56′E) at depths of 166– 162 m, R/ V Dr. Fridtjof Nansen (DFN) stn. 3713, 15 April 2005.

Paratypes. (8 specimens). Angola: CAS 222338, 1 male 51.8+d mm SL+CL, 1 female 52.3+d mm SL+CL, sw. of Congo R. mouth (6°27′S, 11°55′E), 109– 108 m, DFN stn. 3783, 22 April 2005 ; CAS 244059 , 1 male 102.4+d mm SL+CL, same data as for holotype ; CAS 225193 , 1 female 52.2+d mm SL+CL, off Luanda (8°53.5′S, 13°02.21′E) 190– 187 m, DFN stn. 102, 11 March 2007 ; NMW 99079, 1 female 62.6+ 20.2 mm SL+CL, same data as for CAS 222338 . Ghana: CAS 243855 , 1 female 64.1+ 17.4 mm SL+CL, off Accra (5°16.44′N, 0°10.65′W), 91– 88 m, DFN stn. 13, 2 May 2010 ; CAS 243856 , 1 male 51.3+ 15.3 mm SL+CL, off Keta (5°49.26′N, 1°07.57′E), 84– 74 m, DFN stn.4, 1 May 2010 ; CAS 243857 , 1 female 58.6 + d mm SL+CL, se. off Keta , (5°53.89′N, 1°16.37′E), 208– 201 m, DFN stn. 2, 2 May 2010 .

Non-type specimens. (4 specimens). Excluded from type material because of damage and/or juvenile stage. CAS 244060, 4 specimens of undetermined sex (37.9–46.5 mm SL), same data as for holotype.

Diagnosis. Thorogobius alvheimi sp. nov. is distinguished from its congeners in the combination of following characters: Fins: first dorsal fin with six spiny rays, second and third distinctly elongated; pectoral fin ray count 20–21; pelvic disc complete and short with well-developed anterior membrane (frenum), with pointed lateral lobes. Scales: nape and predorsal area naked; no scales on the opercle; scales in longitudinal series 27–31. Pattern of free neuromasts: supratemporal rows tr and trp developed, extending transversally between pores H and K; longitudinal row g short, not passing row m posteriorly and distinctly distant from row h; infraorbital row 6 long, ventrally extending to lower margin of preopercle, its ventral section 6i originating anterior to its dorsal section 6s; posterior lateral row h reaching anteriorly above posterior third of opercle. Body proportions: body depth (16.6– 20.4% at anal-fin origin in SL), head width (42.9–53.8% in head length); upper jaw long (42.6–45.7% in head length); minimum height of caudal peduncle (34.8–50.2% in caudal peduncle length); eyes large (22.4–31.3% in head length); caudal fin short (27.1–32.3% in SL). Coloration: body uniformly pale fawn and brown; margin of scale pockets dark brown pigmented, yielding a reticulated pattern; pale spots on nape and predorsal area; caudal fin uniformly dusky greyish.

Description. Profile of head steep; dorsal outline of body straight. Tubular anterior nostril short without process from rim; branchiostegal membrane attached to side of isthmus.

Fins. D1 with 6 spiny rays (6*: 9); D2 with 1 spiny and 11 articulated rays (1+11*: 9); anal fin with 1 spiny and 10 articulated rays (1+10*: 9); pectoral fin with 20–21 articulated rays (20*: 7, 21: 2); dorsalmost rays of pectoral fin within fin membrane; pelvic disc with 1 spiny and 5 articulated rays on each side (1+5*: 9); caudal fin with 16– 17 segmented rays (16*: 1, 17: 8), 14 of them branched (14*: 9). Second to fourth spiny rays of D1 longest; second spiny ray of D1 extremely elongated, when depressed reaching to end of D2 base; depressed third dorsal spiny ray reaching approximately to first quarter of D2 base. Pelvic disc complete (oval-shaped) with well-developed anterior membrane (frenum) that extends about 75% of first (spinous) ray; lobes distinct, narrow and pointed.

Squamation. Scales in lateral series 27–31 (27: 2, 28: 1, 29*: 3, 30: 1, 31: 1); scales in transversal series 8–11 (8:2; 9: 1; 10*: 1, 11: 1). Entire trunk, breast and base of pectoral fin covered by large scales. Predorsal area, nape, cheek and opercle naked ( Fig. 3 ).

......continued on the next page

Dentition. Premaxillary teeth arranged in an outer row of distinctly larger canine teeth and 5–6 rows of small conical teeth; on dentary some teeth of anteriormost row enlarged and caniniform, followed by series of 5–6 intermediate rows of small conical teeth and innermost row of enlarged teeth.

Gill-rakers (holotype). Eight gill-rakers on ceratobranchial bone; one on epibranchial and one on pharyngobranchial.

Vertebrae. Total number 28; 11 precaudal and 17 caudal, including urostyle.

Body proportions. Presented in table 2.

Head lateral line system ( Fig. 3 ). Anterior and posterior oculoscapular canals complete with pores (from anterior to posterior) B, C (unpaired), D (unpaired), E, F, G, H and K, and L, respectively. Preopercular canal with pores (from dorsal to ventral) M, N and O; these pores larger than pores of other head canals. Rows and number of neuromasts (sensory papillae) given in table 1. Generally a high number of papillae present in most of the neuromast rows.

Coloration (preserved in ethanol). Body pale fawn and brown; head, including nape and predorsal area, darker than trunk; lips not distinctly darker than head; nape and predorsal area with pale spots in a reticulate pattern over dark ground laterally extending onto dorsal part of opercle; neuromasts (sensory papillae) dark brown; margin of scale pockets dark brown, yielding a reticulated pattern. Trunk uniformly pale fawn to brownish; no dark patches at the bases of dorsal fins; caudal, pectoral and pelvic fins uniformly dusky greyish ( Figs. 2 , 3 ).

Etymology. This species is named in honor of Oddgeir Alvheim of the Institute of Marine Research, Bergen, Norway, for his many photographic contributions to the FAO Species Identification Guides and for his assistance and advice to the second author during three surveys aboard the R/V Dr. Fridtjof Nansen.

Distribution and habitat. So far Thorogobius alvheimi sp. nov. is known only from the type localities off Angola and Ghana. It was dredged on the outer edge of the continental shelf from 208– 74m depth and occurs on soft bottom.

Remarks. Thorogobius alvheimi sp. nov. differs distinctly from other species of the genus in the following specific characters (also see table 3 for an additional character matrix).

Thorogobius alvheimi sp. nov. and Thorogobius angolensis differ in: (1) squamation of nape and predorsal area and dorsal part of opercle (naked vs. completely scaled) ( Fig. 7 ); (2) number of neuromasts in head neuromast rows (less numerous and shorter vs. numerous and longer), e.g. row i1 (10–12 vs. 19–25); coloration (preserved) of (3) trunk (uniformly pale fawn to brownish with no distinct markings vs. pale fawn to brownish with two brown blotches on flanks in lateral midline below rear of D1 and center of D2, respectively); of (4) nape and predorsal area (with pale spots in a reticulate pattern over dark ground extending onto dorsal part of opercle vs. no spots on nape, predorsal area or opercle); of (5) pectoral fin (no dark vertical band on dorsal half of pectoral fin base vs. dark band on base of pectoral fin); (6) caudal fin uniformly dusky greyish vs. 4–5 vertical dark bands.

Thorogobius alvheimi sp. nov. and Thorogobius ephippiatus differ in: (1) scales in lateral midline (27–31 vs. 33–42); (2) lobe of pectoral fin (scaled vs. naked); (3) neuromast rows tr and trp (present vs. absent); coloration (preserved) of (4) head, nape and predorsal area (pale spots in a reticulate pattern on nape and predorsal area only vs. brown spots on head, nape and predorsal area); of (5) trunk (uniformly pale fawn to brownish with no distinct markings vs. covered with dark brown blotches); (6) habitat preference (offshore between 74 and 208 m on soft bottoms vs. inshore in 6–60 m on sandy areas of rocky shores, also cave dwelling); (7) distribution (off Angola and Ghana vs. Norwegian Sea to Canary Islands).

Thorogobius alvheimi sp. nov. and Thorogobius laureatus sp. nov. differ in: (1) squamation of nape and predorsal area (naked vs. sides of nape and predorsal area scaled) ( Figs. 3 , 5 , 7 ); (2) pattern of the head neuromast lateral line system (distance between rows g and h as least as long as row g vs. distance between both rows halflength of row g or less; row 6i originates anterior to 6s vs. rows 6i and 6s opposite to each other); coloration (preserved) of (3) nape and predorsal area (with pale spots in a reticulate pattern over dark ground laterally extending on dorsal part of opercle vs. no spots on nape and predorsal area) ( Figs. 3 , 5 ); of (4) pectoral fin (no dark vertical band on dorsal half of pectoral fin base vs. dark band on base of pectoral fin) ( Figs. 2 , 4 , 6 ); of (5) caudal fin (uniformly dusky greyish vs. with 6–7 distinct dark vertical bands) ( Figs. 2 , 6 ).

Thorogobius alvheimi sp. nov. and Thorogobius macrolepis differ in: (1) number of pectoral fin rays (20–21 vs. 17–18); (2) number of neuromasts in head neuromast rows, e.g. r2 (11–20 vs. 4–8), c2 (16–24 vs. 8–13), 3 (12– 22 vs. 8–11), 4 (16–25 vs. 9–13), e1 (32–46 vs. 24–29), f (17–29 vs. 10–15), as1 (16–22 vs. 7–11), la2 (8 vs. 3–7); (3) lobe of pectoral fin (scaled vs. naked); (4) neuromast rows tr and trp (present vs. absent); coloration (preserved) of (5) head, nape and predorsal area (pale spots in reticulate pattern on nape and predorsal area only vs. brown spots on head, nape and predorsal area); of (6) trunk (uniformly pale fawn to brownish with no distinct markings vs. covered with pale spots and blotches); (7) habitat preference (offshore between 74 and 208 m on soft bottom vs. inshore in 6–60 m on sandy areas of rocky shores, also cave dwelling); (8) distribution (off Angola and Ghana vs. from the Mediterranean).

Thorogobius alvheimi sp. nov. and Thorogobius rofeni differ in: (1) neuromast rows tr and trp (present vs. absent); (2) number of neuromasts in head neuromast rows, e.g. r2 (11–20 vs. 5–8), h (18–35 vs. 12–17), as1 (16– 23 vs. 10–13), la2 (8 vs. 4–5); (3) upper jaw longer (42.6–45.7% vs. 33.0–37.2% in head length); (4) coloration (preserved) of (5) nape and predorsal area (with pale spots in a reticulate pattern over dark ground laterally extending on dorsal part of opercle vs. no spots on nape and predorsal area); of (6) caudal fin (uniformly dusky greyish vs. with distinct dark vertical bands).

Figures

FIGURE 1. Map of West Africa, showing sampling sites of Thorogobius angolensis (squares), Thorogobius alvheimi sp. nov. (circles), Thorogobius laureatus sp. nov. (triangles) and Thorogobius rofeni (diamonds).

FIGURE 2. Thorogobius alvheimi sp. nov. Holotype, CAS 222482, female, 72.1 mm SL; Angola. 15 April 2005. A dorsal view, B lateral view. Scale bar = 1 cm.

FIGURE 3. Thorogobius alvheimi sp. nov. Holotype. Detailed view of cephalic neuromast rows and spots on nape and predorsal area. Neuromast rows: s1, n, o, r1, r2, 1, 2, 3, 4, 5s, 5i, 6s, 6i, b, d, z, ot, oi, os, e2, i2, g, m, x1, x2, tr, trp, q, h, y. A dorsal view, B lateral view. Scale bar = 1 cm.

FIGURE 4. Thorogobius laureatus sp. nov. Holotype, CAS 243854, male, 65.1 mm SL; Angola. 22 April 2005. A dorsal view, B lateral view. Scale bar = 1 cm.

FIGURE 5. Thorogobius laureatus sp. nov. Holotype. Detailed view of cephalic neuromast rows and lateral bands of scales on nape and predorsal area. Neuromast rows: s1, n, o, r1, r2, 1, 2, 3, 4, 5s, 5i, 6s, 6i, b, d, z, ot, oi, os, e2, i2, g, m, x1, x2, tr, trp, q, h. A dorsal view, B lateral view. Scale bar = 1 cm.

FIGURE 6. Thorogobius laureatus sp. nov. Paratype, NMW 99080, male, 59.1 mm SL; São Tomé and Príncipe. 18 May 2010. Scale bar = 1 cm.

FIGURE 7. Sketch of the three different squamation patterns (dashed areas) in the predorsal area of the genus Thorogobius. Dorsal view of the head and anteriormost part of the body. A predorsal area without squamation (Thorogobius alvheimi sp. nov., Thorogobius ephippiatus, Thorogobius macrolepis, Thorogobius rofeni), B predorsal area with scaled lateral strips (Thorogobius laureatus sp. nov.), C predorsal area with complete squamation (Thorogobius angolensis).