Austrolebias monstrosus, Wilson J. E. M. Costa, 2006

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: 54-56

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Austrolebias monstrosus

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Austrolebias monstrosus  (Huber), new combination

(Fig. 22)

Cynolebias spinifer  ZBK  non C. spinifer  ZBK  Ahl; Ringuelet et al., 1967: 441 (misidentification of specimens from Ituzaingó and Hickmann, northern Argentina).

Cynolebias monstrosus  ZBK  Huber, 1995: 9 ( type locality: Provincia de Boqueron, near La Serena, upper Chaco basin , Paraguay, 21.94S 56.97W; holotype: MNHN 1994-1110GoogleMaps  ).

Material examined

Paraguay: Boquerón: UMMZ 216569, 1; Linea 10, 12.5 km W of Estancia Heisseque of Dr. Duran, ca. 100 km SW of Filadelfia ; C. Cuevas & L. Naylor, 13 Jun. 1981.  UMMZ 201175, 2; 419 km by road NW Villa Hayes ; P. Myers & G. K. Creighton, 29 Jul. 1977.  Argentina: Salta: ILPLA 995b, 1; San Martin ; Pierotti, 21- 26 Mar. 1950.  ILPLA 996, 12 (2 c&s); Hickmann; no data on collection.  Corrientes: ILPLA 993a, 6 (1 c&s); Ituzaingó; S. Pierotti & D. Budin, 16 Nov. 1950.  MCNI 1142b, 1; Ruta Provincial 52, General de San Martin ; G. Gonzo & M. Fabrezi, 13 Apr. 2005. 


Similar to A. elongatus  and A. prognathus  , and distinguished from all other species of the A. elongatus  group and most other cynolebiatines in possessing some transverse series of small scales on anal-fin base in male, contact organs on the outer surface of the pectoral fin and on caudal fin in male, long jaws (lower jaw 29.3-36.4 % head length in males), and numerous gill-rakers on the first branchial arch (5-6 + 14-16). Similar to A. elongatus  and other congeners by the presence of minute scales on the pectoral-fin and caudal-fin bases in older males. Differs from A. elongatus  in having gray bars on flanks in males and fewer dorsal-fin rays in males (16-18 vs. 18-20).


Morphometric data appear in Table 3. Males larger than females, largest male examined 115.8 mm SL, largest female 64.6 mm SL. Dorsal profile slightly concave on head, convex from snout to end of dorsal-fin base, approximately straight on caudal peduncle; no distinctive adipose ridge on frontal region. Ventral profile slightly 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 moderately slender to deep in older specimens, slightly compressed. Snout profile pointed, jaws elongated.

Tip of both dorsal and anal fins rounded. Anteromedian rays of anal fin of females not lengthened; distal portion of anal fin thickened in females. Caudal fin rounded. Pectoral fins elliptical, posterior margin on vertical between pelvic-fin base and urogenital papilla. Tips of pelvic fins reaching between base of 1st and 3rd anal-fin rays. Pelvic-fin bases separated by interspace. Urogenital papilla not attached to anal fin. Dorsal-fin origin on vertical between base of 5th and 6th anal-fin rays; dorsal-fin origin between neural spines of 15th and 18th vertebrae; anal-fin origin between pleural ribs of 12th and 15th vertebrae. Dorsal-fin rays 16-18 in males, 15-16 in females; anal-fin rays 21-23 in both sexes; caudal-fin rays 31-35; pectoral-fin rays 13; pelvic-fin rays 5-6.

Scales very small, cycloid, and irregularly arranged. Entire trunk scaled, except just above anal-fin base in females. Head scaled, except anterior third of frontal region and ventral surface. Small scales with prominent contact organs covering about half of caudal fin, one third of anal fin, and pectoral-fin base in males; sometimes few scales on dorsalfin base. Frontal scales small, restricted to posterior frontal portion, without a clear arrangement pattern; E-scales not overlapping medially. Longitudinal series of scales about 60-75; transverse series of scales about 20-30; series of scales around caudal peduncle about 30-40. One to five prominent contact organs on each scale of flank and opercle in males. Row of contact organs on inner surface of all pectoral-fin rays, outer surface of upper pectoral-fin rays, lateral surface of entire anal-fin rays, and distal portion of dorsal-fin rays and caudal-fin rays in males.

Cephalic neuromasts: supraorbital 36-37, parietal 4, anterior rostral 5, posterior rostral 3, infraorbital 6 + 36, preorbital 2, otic plus post-otic 25, supratemporal 2-3, median opercular 1, ventral opercular 3, preopercular plus mandibular 65, lateral mandibular 10. Basihyal subtriangular, width about 85 % of length; basihyal cartilage short, about 35 % of total basihyal length, without lateral projections. Six branchiostegal rays. One tooth on second pharyngobranchial. Gill-rakers on first branchial arch 5-6 + 15-16. Dermosphenotic ossification absent. Ventral process of posttemporal long. Total vertebrae 35-39.


Males: sides of body dark yellowish brown to dark gray, often with 13-15 pale gray bars. Urogenital papilla gray. Opercular and infraorbital regions dark brownish golden; approximately rectangular, elongate black infraorbital bar; dark gray supraorbital spot. Iris reddish brown, with dark brown bar through center of eye. Unpaired fins dark brown with dark yellow rays; pink iridescence on distal portion of dorsal fin. Pelvic fins dark gray. Pectoral fins hyaline.

Females: sides of body dark brown, sometimes with pale gray bars; no dark spot on anterocentral portion of flank and caudal peduncle. Opercular region pale golden. Iris reddish brown, with dark brown bar through center of eye. Dark gray infraorbital bar and faint gray supraorbital spot. Fins hyaline.


Río Paraguay-Paraná basin in Paraguay and northern Argentina (Fig. 18). According to Karina Osinaga (pers. com., 2004), this species also occurs in the Bolivian Chaco.