Spectrolebias gracilis, Costa, Wilson J. E. M. & Amorim, Pedro F., 2018

Costa, Wilson J. E. M. & Amorim, Pedro F., 2018, A new miniature cryptic species of the seasonal killifish genus Spectrolebias from the Tocantins River basin, central Brazil (Cyprinodontiformes, Aplocheilidae), Zoosystematics and Evolution 94 (2), pp. 359-368 : 359

Spectrolebias gracilis sp. n. Figs 4, 5; Table 2

Holotype.

UFRJ 6440, male, 19.2 SL; Brazil: Tocantins state: Alvorada do Tocantins municipality: temporary lagoons close to the Canabrava River, a tributary of the Santa Teresa River, middle Tocantins River basin, road TO-373, 12°29 ’46” S, 49°00 ’51” W, altitude about 290 m asl; W. J. E. M. Costa et al., 16 Apr. 2006.

Paratypes.

UFRJ 6441, 5 males, 18.9-20.8 mm SL, 3 females, 16.1-17.8 mm SL; UFRJ 6442, 3 males, 18.7-19.1 mm, 1 female, 16.8 mm SL (C&S); collected with holotype. UFRJ 9300, 2 males, 19.6-19.7 mm SL, 2 females, 18.4-18.5 mm SL; type locality area, 12°29 ’45” S, 49°00 ’28” W, altitude about 290 m; W. J. E. M. Costa et al., 26 Feb. 2013. - UFRJ 9593, 2 males, 19.9-20.0 mm SL, 2 females, 16.2-16.8 mm SL; UFRJ 9299, 4 males, 18.5-20.5 mm SL, 1 female, 19.2 mm SL; Goiatins municipality, temporary pool in the floodplains of the right bank of the Tocantins River, near Palmeirante, 07°53 ’02” S, 47°55 ’45” W, altitude about 170 m asl; W. J. E. M. Costa et al., 28 Feb. 2013. - UFRJ 10802, 9 males, 15.8-17.6 mm SL, 22 females, 13.0-17.4 mm SL; UFRJ 10803, 3 males, 16.3-20.7 mm SL, 3 females, 13.9-15.3 mm SL (C&S); CICCAA 00692, 5 males, 16.2-17.2 mm SL, 5 females, 14.6-16.0 mm SL; same locality; A.C. de Luca, 2012.

Diagnosis.

Spectrolebias gracilis is member of a clade endemic to the Araguaia-Tocantins River System, also including S. costae , S. semiocellatus Costa & Nielsen, 1997 and S. inaequipinnatus Costa & Brasil, 2008, and morphologically diagnosed by: dorsal and anal fins in males with iridescent dots restricted to the basal portion of fins (vs. scattered over the whole fin), caudal fin in males hyaline (vs. variably coloured, usually dark red or grey), caudal-fin base with two pairs of neuromasts (vs. one). Spectrolebias gracilis is similar to S. costae and distinguished from S. semiocellatus and S. inaequipinnatus by having dorsal fin rounded in males (vs. pointed), dark brown to black pigmentation on the flank in males (vs. light brownish grey), and a subdistal bright blue stripe on the dorsal and anal fins in males (vs. subdistal bright blue absent). Spectrolebias gracilis differs from S. costae by the iridescent light blue colour pattern in males, comprising the presence of 10-12 small blue spots irregularly arranged on opercle, surrounded by diffuse blue iridescence (Fig. 4; vs. 6-8 small blue spots, usually arranged in three vertical series, contrasting with dark brown colour ground, Fig. 3) and one or two series of dots irregularly arranged on the basal portion of the dorsal fin (Fig. 4; vs. blue dots arranged in single longitudinal row close to fin base, Fig. 3).

Description.

Morphometric data is given in Table 2. Largest male examined 20.8 mm SL; largest female examined 18.5 mm SL. Body relatively deep, compressed. Greatest body depth in vertical through pelvic-fin insertion. Dorsal profile convex between snout and posterior end of dorsal fin, nearly straight and horizontal on caudal peduncle; ventral profile convex between lower jaw and pectoral-fin base, approximately straight and moderately steep between pelvic-fin base and posterior end of anal fin, nearly straight and horizontal on caudal peduncle. Urogenital papilla short and cylindrical in males, globular in females. Head moderately wide, sub-triangular in lateral view. Jaws short, teeth numerous, conical, irregularly arranged; outer teeth hypertrophied, inner teeth small and numerous. Vomerine teeth 13. Gill-rakers on first branchial arch 2 + 7, gill-rakers short, straight, without denticles. Head narrow, sub-triangular in lateral view. Snout short, blunt. Jaws short, premaxilla and dentary teeth conical, small, numerous, irregularly arranged, except for external series with longer fang-like teeth. Vomerine teeth absent. Dermosphenotic absent. Gill-rakers on first branchial arch 2 + 8-9. Six branchiostegal rays. Total vertebrae 26-27.

Dorsal and anal fins rounded, broader and fan-shaped in males, without filamentous rays. Caudal fin subtruncate, dorsal and ventral margins nearly straight, posterior margin gently convex. Pectoral fin elliptical, posterior margin reaching vertical between base of fifth and sixth anal-fin rays in males, reaching urogenital papilla in females; in males, minute contact organs on two uppermost pectoral-fin rays. Pelvic-fin small, tip reaching between second and third anus anal-fin ray in males, between first and second anal-fin ray in females; pelvic-fin bases medially in close proximity. Dorsal-fin origin in vertical between base of 3rd and 5th anal-fin rays in males, between base of 4th and 6th anal-fin rays in females. Dorsal-fin origin between neural spines of vertebrae 7 and 8 in males, between neural spines of vertebrae 9 and 10 in females; anal-fin origin between pleural ribs of vertebrae 6 and 7 in males, between pleural ribs of vertebrae 7 and 8 in females. Hypurals ankylosed, forming single hypural plate. Ventral process of posttemporal absent. Dorsal-fin rays 21-23 in males, 15-18 in females; anal-fin rays 23-25 in males, 19-21 in females; caudal-fin rays 21-23; pectoral-fin rays 12-13; pelvic-fin rays 5-6.

Scales small, cycloid. Body and head entirely scaled, except anterior ventral surface of head. Body squamation extending over anterior 20% of caudal-fin base; no scales on dorsal, anal and pectoral-fin bases. Longitudinal series of scales 24-25; transverse series of scales 9-10; scale rows around caudal peduncle 12. No contact organs on scales. Total vertebrae 26-27. Frontal squamation E-patterned; E-scales overlapping medially; anterior-most frontal G-scale.

Latero-sensory canals absent. Cephalic neuromasts: supraorbital 11-13, parietal 3-4, anterior rostral 1, posterior rostral 1, infraorbital 1 + 16-20, preorbital 3, otic 2, post-otic 2, supratemporal 1, pre-opercular 11-14, median opercular 1, ventral opercular 1, mandibular 6-7, lateral mandibular 3-5, paramandibular 1. One or two neuromasts per scale of trunk lateral line. Two pairs of neuromasts on caudal-fin base.

Colouration in life.

Males (Fig. 4). Body dark purplish brown to black; posterior-most extremity of caudal peduncle light pinkish brown; minute bright blue dots irregularly scattered over flank, more concentrated on its anterior portion. Head brown to black, with 10-12 small bright blue spots irregularly arranged on opercle, surrounded by diffuse blue iridescence; two bright blue bars on suborbital region. Iris dark brown, with two bright blue bars. Dorsal and anal fins dark reddish grey to black, with sub-distal bright blue line; light blue dots irregularly scattered over basal portion of both fins. Caudal fin hyaline, with light blue dots irregularly scattered over its basal portion; posterior margin bluish white. Pectoral fin hyaline with bright blue dots on basal portion. Pelvic fin dark grey to black, with subdistal bright blue stripe.

Females (Fig. 5). Body pale brown, with irregularly arranged, vertically elongated dark brown blotches, more concentrated on its anterior portion. Opercular region and venter with greenish golden iridescence. Two black bars on suborbital region. Iris dark brown, with two brownish yellow bars. Dorsal and anal fins hyaline, with small dark brown spots. Caudal and paired fins hyaline.

Etymology.

From the Latin gracilis , meaning thin, referring to the thin body of the small-sized new species.

Distribution and habitat.

Spectrolebias gracilis is known from temporary pools of two localities of the middle Tocantins River basin, central Brazil (Fig. 6). In both localities pools were shallow, about 80 cm in deeper places, and densely occupied by aquatic vegetation.