Glaucostegus younholeei, Habib & Islam, 2021

Habib, Kazi Ahsan & Islam, Md Jayedul, 2021, Description of a new species of giant guitarfish, Glaucostegus younholeei sp nov. (Rhinopristiformes: Glaucostegidae) from the northern Bay of Bengal Bangladesh, Zootaxa 4995 (1), pp. 129-146 : 132-135

Glaucostegus younholeei , sp. nov.

English common name: Bangladeshi guitarfish

Local common name: Pitambori

Zoobank No. urn:lsid:zoobank.org:act:B87849B0-4052-4439-8937-C3DE6DBD78A5

Holotype. R1911 CB-04, adult male 933 mm TL ( Fig. 2 ), Bangladesh, Cox’s Bazar ( Fig. 1 ); collected by K.A. Habib and M.J. Islam; 10 November 2019.

Paratypes. 12 specimens: 4 specimens collected with holotype: R1911 CB-01 (adult male 794 mm), R1911 CB- 02 (female 760 mm), R1911 CB-03 (adult male 831 mm), R1911 CB-05 (adult male 901 mm); collected by K.A. Habib and M.J. Islam; 10 November 2019; 08 specimens: R2001 CB-01 (female 853 mm), R2001 CB-02 (adult male 730 mm), R2001 CB-03 (female 828 mm), R2001 CB-04 (female 764 mm), R2001 CB-05 (adult male 893 mm), R2001 CB-07 (adult male 735 mm), R2001 CB-08 (adult male 868 mm), R2001 CB-09 (adult male 846 mm); collected by K.A. Habib and M.J. Islam; 09 January 2020 .

Diagnosis. Moderately large, brownish or greyish guitarfish with a narrowly wedge-shaped disc, moderately long, triangular and bluntly pointed snout, and broad oblique nostrils with the narrow anterior opening. Disc thickened centrally, length 1.30–1.45 in width; Snout acute, angle 31–40°, tip bluntly pointed and never protruding forward as a distinct lobe. Orbit relatively large in adults, diameter 8.19–11.62 in preorbital length, 2.25–2.69 in interorbital distance. Rostral ridges almost joined along their entire length; margin of cranium sharply demarcated before eyes. Spiracular folds very short and widely separated.

Nostrils about half of the mouth width, subequal (0.98–1.33) to internasal width; ~55–57 nasal lamellae; anteri- or nasal flaps slightly penetrating into internasal space, their interspace equal to 2.20–2.61 in length of the posterior nasal aperture. Skin rough, densely covered with small denticles, more coarsely granular on the dorsal surface than ventrally, enlarged between orbits and in a distinct band between nape and first dorsal fin. Pair of 2 large thorns on each shoulder and similar thorns in irregular, median row(s) along mid-line. Tail longer, length 1.15–1.48 in disc length; dorsal fins narrowly spaced, interspace 1.32–2.11 in base length of the first dorsal fin. Clasper length in adult male 4.37–5.70 in total length. Morphometric measurements are given in Table 1.

Description. Moderately large, brownish or greyish guitarfish with a narrowly wedge-shaped disc, with 730– 933 mm total length (matured). Disc broadly wedge-shaped, angular anteriorly, outer margins broadly rounded, narrowly rounded distally, its length 1.44 (1.30–1.45) in width. Pelvic fins elongate, short-based, its length 2.78 (2.07– 2.78) in width, 1.61 (1.44–1.98) in base length; anterior margin weakly concave anteriorly then becoming straight to weakly convex, apex broadly rounded, posterior margin almost straight. Tail moderately elongate, slen- der anteriorly, tapering weakly; tail length 1.39 (1.15–1.48) in disc length.

Head moderately elongate; snout moderately long, triangular and bluntly pointed ( Fig. 2 , 3 , 4 ), snout length 3.67 (3.54–4.38) in inter-spiracular length, 9.27 (8.19–11.62) in orbit diameter, 3.90 (3.54–4.47) in interorbital distance; preoral length 2.54 (2.29–2.98) in mouth width, 5.25 (4.53–6.68) in internarial distance. Interorbital space almost flat, eyes moderately large, not elevated or protruding. Orbit relatively large in adults, diameter 9.27 (8.19–11.6) in preorbital length, 1.10 (0.79–1.21) in spiracle length, 2.38 (2.25–2.69) in interorbital distance. Spiracles relatively very small and weakly developed. Nostril moderately large, oblique, nasal flaps well developed ( Fig. 4B & C ). Anterior aperture rectangular, width exceeding in its length; nostril 1.76 (1.72–2.03) in mouth width, nostril length 1.79 (1.79–5.60) in anterior aperture width, 2.39 (2.32–4.67) in anterior nasal-flap base length, 1.17 (0.98–1.33) in internarial distance. Anterior nasal flap moderately long, flap base length 1.65 (1.00–1.92) in width, flap width 2.21 (0.83–2.21) in anterior aperture width. Anterior nasal flaps slightly penetrating into internasal space, their interspace equal to 2.59 (2.20–2.61) in length of the posterior nasal aperture ( Fig. 5 ).

02, R1911CB-03, R1911CB-05, R2001CB-01, R2001CB-02, R2001CB-03, R2001CB-04, R2001CB-05, R2001CB-07,

R2001CB-08 and R2001CB-09 of Glaucostegus younholeei sp. nov.

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Caudal peduncle length (dorsal) 45.10 4.83 4.20-–5.54

Body width—pelvic insertion (tail) 103.00 11.04 9.32–10.75

Disc width—anterior orbit 143.30 15.36 13.88–17.15

Body width—first dorsal-fin origin 78.40 8.40 7.03–8.20

Body width—second dorsal-fin origin 46.00 4.93 3.80–4.83

Body depth—maximum (scap) 58.00 6.22 5.17–7.57

Body depth—pelvic-fin insertion 46.20 4.95 4.54–6.09

Body depth—first dorsal-fin origin 42.00 4.50 3.93–4.41

Body depth—second dorsal-fin origin 32.00 3.43 2.80–3.29

Tail length 530.00 56.81 51.32–57.26 Distance between posterior nasal flap 52.00 5.57 4.87–6.13

Tail length from anterior cloaca 559.00 59.91 54.21–59.79 Precloacal length 374.00 40.09 40.21–45.79

Cloaca 29.00 3.11 2.53–3.26

Clasper length 205.00 21.97 17.55–22.17* *Clasper length without female paratypes

Dermal fold lateral on tail, originating well behind the free rear tip of pelvic fin, reaching just behind the ventral caudal-fin origin, fold moderately well developed. Mouth width 1.76 (1.72–2.03) in nostril length, 6.23 (5.8–6.70) in precloacal length, positioned slightly forward of hind margin of orbit. Upper jaw weakly convex, upper lip arched slightly, lower lip pronounced, separated from oral groove by ridges of strongly crenelated skin.

Teeth small, blunt, crowns rhomboidal with weak, pointed posterior cusps; upper and lower jaw teeth similar in shape and size, tooth rows in upper jaw 84 (58–69) ( Fig. 4A ). Length of third-gill slit 2.00 (1.75–2.13) in nostril length, 4.94 (4.88–7.13) in distance between fifth-gill slits; distance between first-gill slits 1.36 (0.73–1.96) in distance between fifth-gill slits; distance between fifth-gill slits 2.90 (2.65–4.43) in internarial distance, 1.40 (1.30–1.82) in mouth width.

Dorsal fins rather short; apices narrowly rounded to angular; anterior margins weakly convex; posterior margins weakly concave; free rear tips almost forming a right angle; first dorsal fin slightly taller and more upright than second, length 1.17 (1.17–1.46) in height; second dorsal-fin length 1.15 (1.10–1.55) in height. First dorsal fin well behind of pelvic-fin insertion, interspace 2.16 (1.73–2.21) in inter-dorsal distance; inter-dorsal space moderate 1.03 (0.94–1.29) in second dorsal-fin height, 1.43 (1.32–2.11) in first dorsal-fin base, 1.04 (1.04–1.15) in tail width at origin of first dorsal fin ( Fig. 6 ). Caudal fin relatively small, deep and short. Clasper length in adult male 4.55 (4.37–5.70) in total length (TL) ( Fig. 7 ).

Skin rough, densely covered with small denticles; more coarsely granular on the dorsal surface than ventrally, enlarged between orbits and in a distinct band between nape and first dorsal fin. Pair of large thorns on each shoulder and a middorsal band of strong thorns on the back ( Fig. 8 ). Rostral ridges almost joined along their entire length; margin of cranium sharply demarcated before eyes ( Fig. 2 , 3 & 4 ). Snout acute, angle 31–40°; tip bluntly pointed and never protruding forward as distinct the lobe ( Fig. 4B & C ).

Coloration in freshly observed specimen. Brownish on dorsal surface of body; rostrum pale white, rostral ridge brown; snout tip brownish white; pale yellowish around margin of disc, pelvic fins, spiracles and along upper lateral skin fold; eyes golden, pupils dark-bluish black, orbital membrane similar to disc color; anterior half of first and second dorsal fin light brown in color; first and second dorsal fin base, posterior half of fins similar to body; caudal fin similar to body color. Ventral surface mostly white with yellowish; oronasal region white, snout opposite dappled brownish; broad dusky margins on both posterior disc and pelvic fins ( Fig. 2 ).

Coloration in preserved condition. Brownish gray on dorsal surface of body; rostral cartilage greyish white, rostral ridge gray; snout tip pale white; dark gray around margin of disc, pelvic fins, spiracles and along upper lateral skin fold; eyes golden, pupils black, orbital membrane similar to disc color; first and second dorsal fin anterior half brownish gray in color; first and second dorsal fin base, posterior half of fins similar to body; caudal fin similar to body color. Ventral surface mostly white with greyish; oronasal region pale white, snout opposite dark gray ( Fig 3 ).

Distribution. Glaucostegus younholeei sp. nov. is currently known only from the Bay of Bengal, Bangladesh. It may also occur in the adjacent sea areas like Andaman Sea, Arabian Sea, Malacca Strait and the Gulf of Thailand.

Etymology. We dedicate the new species name “younholeei” in the honour of Dr. Youn-Ho Lee, the PhD supervisor of the first author and Principal Research Scientist/Professor and Vice-President of Korea Institute of Ocean Science and Technology (KIOST), who significantly contributed to the knowledge of marine biodiversity, DNA barcoding and population genetics of marine organisms in the Western Pacific and north Bay of Bengal. The common name “Bangladeshi guitarfish” refers to its occurrence in the Bay of Bengal.

Remarks. The new species Glaucostegus younholeei differs from its similar species G. granulatus in relatively smaller size in adults (total length 730–933 mm verses at least 2290 mm); Snout relatively more pointed, angle 31–40° vs. 46–52°; relatively large orbit in adults, diameter 2.25–2.69 vs. 2–3.8 in interorbital space, 8.19–11.62 vs. 9.00–16.00 in preorbital length; distance between anterior nasal flap relatively larger 2.20–2.61 vs. 2.2–3.2 in length of posterior nasal aperture; relatively short inter-dorsal distance 1.32–2.11 vs. 1.3–1.6 in first dorsal fin base length.

The new species differs from G. halavi in having relatively small disc length 1.30–1.45 vs. 1.2–1.3 in width; snout tip bluntly pointed, angle 31–40° vs. ~65°; orbit small in adults, diameter 8.19–11.62 vs. 6.3–7.8 in preorbital length; nostrils relatively large about half of the mouth width vs. 2/3 of the mouth width; nasal lamellae ~55–57 vs. ~61.

Glaucostegus younholeei is distinguished from G. obtusus in having relatively small disc length 1.30–1.45 vs. ~ 1.2 in width; snout tip bluntly pointed, angle 31–40° vs. ~80°; orbit relatively small, diameter 8.19–11.62 vs. ~ 6.5 in preorbital length; tail relatively longer in length 1.15–1.48 vs. 1.4–1.6 in disc length; inter-dorsal distance 1.32–2.11 vs.> 2 in first dorsal fin base length.

Glaucostegus younholeei is also separate from G. petiti in having relatively small eye diameter 8.19–11.62 vs. 7.00 in preorbital length; nostril 1.72–2.03 vs. 1.5 in internasal width; nasal lamellae ~55–57 vs. ~50–52; moreover, it is endemic to Madagascar (Frick et al., 2018, 2021).

The new species is distinguished from G. thouin in having snout tip bluntly pointed (31–40°) and never protruding forward as distinct lobe vs. snout tip narrowly oval (~55°) and protruding well forward; nostril width about half of the mouth width vs. nostril almost same of the mouth width, nostril 0.98–1.33 vs. ~ 1.9 in internasal distance; distance between anterior nasal flap relatively smaller 2.20– 2.61 vs. ~ 1.5 in length of posterior nasal aperture; nasal lamellae ~55–57 vs. ~84; tail relatively larger in length 1.15–1.48 vs. ~ 2 in disc length; inter-dorsal distance 1.32–2.11 vs. 2–2.5 in first dorsal fin base length.

Glaucostegus younholeei is distinct from G. typus in having relatively large disc length 1.30–1.45 vs. 1.2–1.3 in disc width; snout tip bluntly pointed, angle 31–40° vs. 46–52°; orbit relatively small, diameter 8.19–11.62 vs. 6.1–7.8 in preorbital length, and 2.25–2.69 vs. 1.8–2.4 in interorbital space; nostril width about half of the mouth width vs. nostril almost same of the mouth width; nasal lamellae ~55–57 vs. ~94; tail relatively longer in length 1.15–1.39 vs. 1.3–1.5 in disc length, inter-dorsal distance 1.32–2.11 vs.> 2 in first dorsal fin base length.

Lastly, Glaucostegus younholeei also differs from G. cemiculus in having relatively small disc length 1.30–1.45 vs. 1.2–1.3 in disc width; snout tip bluntly pointed, angle 31–40° vs. 59–63°; orbit very small in adults, diameter 8.19–11.62 vs. 5–6 in preorbital length; relatively small orbit diameter 2.25–2.69 vs. 1.5–2 in interorbital space, nostril 0.98–1.33 vs. 1.40 in internasal width; nasal lamellae ~55–57 vs. ~81; tail length 1.15–1.48 vs. ~ 1.5 in disc length; moreover, G. cemiculus is restricted in Eastern Central Atlantic; Portugal to Angola, including Mediterranean Sea ( Last et al., 2016a).

Genetic description. The COI barcode sequences of G. younholeei obtained from thirteen specimens of the present study and another two sequences submitted to GenBank from Bangladesh revealed only two haplotypes. Genetic divergence between these two haplotypes was 0.02%. Phylogenetic analysis formed a well-resolved tree of relationships at the species level ( Fig. 9 ). In the ML tree, all of the sequences of G. younholeei clustered as a separate group from other congeneric species with the higher bootstrap value of over 90%. The closely related species G. granulatus diverged from the new species G. younholeei forming a deeper and fully separate clade in the phylogeny with 100% bootstrap support. Further, the species G. thouin made more distinct and deeper clade from G. granulatus with 95% bootstrap support ( Fig. 9 ). So, these two species G. granulatus and G. thouin are phylogenetically closer to the new species G. younholeei than other congeneric species, and the average genetic distances between them were found 3.1% and 3.9%, respectively. Genetic divergence of G. younholeei from its all of the congeneric species used in the phylogenetic analysis varied between 3% and 18.3%.

Figures

FIGURE 1. Map showing the collection site (▼) of BFDC fish landing center, Cox’s Bazar, Bangladesh and the Bay of Bengal.

FIGURE 2. Fresh specimen of Glaucostegus younholeei sp. nov.: A. Dorsal view of adult male holotype, 933 mm TL (R1911CB-04); B. Ventral view of adult male holotype, 933 mm TL (R1911CB-04); C. Dorsal view of female paratype, 853 mm TL (R2001CB-01); D. Ventral view of female paratype, 853 mm TL (R2001CB-01).

FIGURE 3. Preserved specimen of Glaucostegus younholeei sp. nov.: A. Dorsal view of adult male holotype, 933 mm TL (R1911CB-04); B. Ventral view of adult male holotype, 933 mm TL (R1911CB-04); C. Dorsal view of female paratype, 828 TL (R2001CB-03), D. Ventral view of female paratype, 828 mm TL (R2001CB-03).

FIGURE 4. Preserved holotypes of adult male Glaucostegus younholeei sp. nov. (R1911CB-04, 933 mm TL): A. Mouth showing the teeth; B. Dorsal view of head, snout, and nostril, C. Ventral view of head, snout, and nostril.

FIGURE 5. Preserved holotypes of adult male Glaucostegus younholeei sp. nov. (R1911CB-04, 933 mm TL): A. Views of oronasal region, B. Views of orbit and spiracle.

FIGURE 6. Lateral views of the unpaired fins of preserved Glaucostegus younholeei sp. nov., adult male holotype (R1911CB- 04): A. Tail folds, B. First dorsal fin, C. Second dorsal fin, D. caudal fin.

FIGURE 7. Showing the left and right clasper of adult male holotype of preserved Glaucostegus younholeei sp. nov. (R1911CB- 04; clasper length 205 mm).

FIGURE 8. A, B & C showing the thorns position of adult male holotype of preserved Glaucostegus younholeei sp. nov. (R1911CB-04).

FIGURE 9. Maximum-likelihood tree constructed for COI gene sequences of Glaucostegus younholeei sp. nov. and its genetically closely related congeneric species retrieved from GenBank. Values of bootstrap support of>80% are shown above branches. Scale bar indicates number of nucleotide substitutions per site.