Wilson J. E. M. Costa, 2006, The South American annual killifish genus Austrolebias (Teleostei: Cyprinodontiformes: Rivulidae): phylogenetic relationships, descriptive morphology and taxonomic revision., Zootaxa 1213, pp. 1-162: 113-117
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Austrolebias arachan ZBK Loureiro, Azpelicueta & García, 2004: 23 ( type locality: pond close to Ruta 7 and arroyo Chuy [ rio Tacuari drainage], laguna Merin basin [laguna dos Patos system] , Departamento de Cerro Largo, Uruguay [approximately 32°15’S 54°00’]; holotype: ZVC-P 4336GoogleMaps ).
Uruguay: Cerro Largo, río Tacuarí drainage: UFRJ 6143, 10; UFRJ 6144, 8 (c&s); CTL 1495, 139; temporary pool near arroyo Chuy , 32°14.56’S 54º3.83’W; P. Laurino et al., 29 Aug. 2004.GoogleMaps UFRJ 6142, 5; CTL 210 b, 13; temporary pool in Parque Rivera, Melo , 32°22.46”S 54º11.32”W; P. Laurino et al., 18 Aug. 2002.GoogleMaps CTL 411, 1; idem ; no data on collectors and date.GoogleMaps Cerro Largo, río Negro drainage: UFRJ 6145, 4; CTL 1490a, 10; Ruta 26, km 372 , 32°17.29’S 54º48.27’W; P. Laurino et al., 29 Aug. 2004.GoogleMaps CTL 200a, 1; idem ; P. Laurino et al., 17 Aug. 2002.GoogleMaps UFRJ 6146, 6; UFRJ 6147, 6 (c&s); CTL 1493a, 12; temporary pool near rio Negro, Paso de Mazangano, Ruta 44 , 32°6.68’S 54º39.96’W; P. Laurino et al., 29 Aug. 2004.GoogleMaps Tacuarembó, río Negro drainage: CTL 186a, 2; Ruta 26, km 331 , 32°5.45’S 55º8.90’W; P. Laurino et al., 17 Aug. 2002.GoogleMaps
Distinguished from all other species of the A. bellottii group by the following combination of features: no prominent contact organ on anal fin in males, urogenital papilla not attached to anal fin, dorsal-fin origin slightly anterior to anal-fin origin in males, flanks dark brown to black, with narrow bright bars in males, anal-fin rays 21-25 in males, 18-22 in females, longitudinal series scales 26-29, frontal squamation E or F- patterned, and vertebrae 28-30.
Morphometric data appear in Table 8. Males larger than females, largest male examined 45.8 mm SL, largest female 26.9 mm SL. Dorsal profile convex from snout to end of dorsal-fin base, approximately straight on caudal peduncle; sometimes weak adipose ridge on posterior portion of frontal region of head in males, making dorsal profile of head slightly concave. Ventral profile convex from lower jaw to end of anal-fin base, nearly straight on caudal peduncle. Greatest body depth at level of pelvic-fin base. Body deep and compressed. Snout blunt and jaws short.
Tip of both dorsal and anal fins rounded. Anteromedian rays of anal fin of females lengthened, anal fin shape nearly triangular; distal portion of anal fin thickened in females. Caudal fin rounded. Pectoral fins elliptical, posterior margin on vertical between base of 2nd and 5th anal-fin rays in males, between anus and urogenital papilla in females. Tip of each pelvic fin reaching between base of 2nd and 3rd anal-fin ray in males, between urogenital papilla and base of 2nd anal-fin ray in females. Pelvic-fin bases medially united, sometimes medial pelvic-fin membranes about 25 % coalesced. Urogenital papilla not attached to anal fin, sometimes thin membrane connecting papilla base to 1st anal-fin base. Dorsal-fin origin slightly anterior to anal-fin origin in males, anal-fin origin on vertical between base of 1st and 3rd dorsal-fin rays; dorsal-fin origin slightly anterior or posterior to anal-fin origin in females; dorsal-fin origin between neural spines of 7th and 9th vertebrae in males, between neural spines of 10th and 12th vertebrae in females. Analfin origin between pleural ribs of 7th and 9th vertebrae in males, between pleural ribs of 9th and 11th vertebrae in females. Dorsal-fin rays 21-26 in males, 16-20 in females; anal-fin rays 21-25 in males, 18-22 in females; caudal-fin rays 22-25; pectoral-fin rays 12-13; pelvic-fin rays 5-6.
Scales large and cycloid. Trunk and head entirely scaled, except ventral surface of head. No scales on dorsal and anal-fin bases, and three rows of scales on caudal-fin base. Frontal squamation often E-patterned, sometimes F -patterned; E-scales overlapping medially; scales arranged in transverse pattern. Longitudinal series of scales 27-29, scales regularly arranged to slightly irregularly in larger male specimens; transverse series of scales 12-15; scale rows around caudal peduncle 18-20. Four to five minute contact organs, sometimes middle slightly more, on each scale of ventral portion of flank in males, sometimes inconspicuous. Row of minute contact organs on uppermost pectoral-fin ray in males, sometimes on second and third rays; sometimes minute contact organs on distal portion of anteriormost anal-fin rays in males. No contact organ on dorsal and caudal fins.
Cephalic neuromasts: supraorbital 17-22, parietal 3, anterior rostral 1, posterior rostral 1, infraorbital 2-3 + 21-29, preorbital 2, otic 2-4, post-otic 3-5, supratemporal 1, median opercular 1, ventral opercular 1-2, preopercular plus mandibular 25-31, lateral mandibular 4-7.
Basihyal nearly triangular, width about 65 % of length; basihyal cartilage long, about 55 % of total basihyal length, with pronounced lateral projection. Six branchiostegal rays. Three or four teeth on second pharyngobranchial. Gill-rakers on first branchial arch 3 + 11-12. Dermosphenotic ossification absent. Ventral process of posttemporal long or short. Total vertebrae 28-30.
Males: sides of body dark brown to black, with 6-11 narrow yellowish white bars, anterior bars wider, posterior bars often represented by white spots; sometimes faint similar bars through dark zones. Urogenital papilla gray. Sides of head dark brown; opercular and infraorbital regions bright greenish blue; approximately rectangular dark gray infraorbital bar; subtriangular dark gray supraorbital bar, not extending to neuromast parietal series. Iris dark yellow, with dark brown bar through center of eye. Unpaired fins dark gray, with small yellowish to bluish white spots on basal portion, spots vertically elongated on dorsal-fin base; distal half of dorsal fin and dorsal portion of caudal fin with pink iridescence; distal half of anal and caudal fins with blue iridescence. Pelvic fins dark bluish gray. Pectoral fins grayish hyaline, with black ventral margin.
Females: sides of body light yellowish brown, with vertical rows of elongate gray spots, sometimes forming gray bars; venter pale golden; rarely a black spot on anterocentral portion of flanks; no black spot on posterior portion of caudal peduncle. Opercular region pale greenish yellow. Iris light yellow, with gray bar through center of eye. Infraorbital and supraorbital bars gray. Unpaired fins hyaline, with pale gray spots on basal portion; paired fins hyaline.
Río Tacuarí drainage, laguna dos Patos system, and río Negro drainage, río Uruguay basin, northeastern Uruguay (Fig. 18).