Oryzias orthognathus Kottelat 1990
Creators: name: Parenti, Lynne R.
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Beloniformes
Adrianichthyidae
Oryzias
Oryzias orthognathus

description: ORYZIAS ORTHOGNATHUS KOTTELAT, 1990A   
SHARPJAWED BUNTINGI  
FIGURES 29B, 51  
 Oryzias orthognathus Kottelat, 1990a: 54–56, fig. 3, tables 1 and 2 [type locality: Indonesia: Sulawesi Tengah, Lake Poso, eastern shore between Tentena and Peura].- Kottelat et al., 1993: 90 [listed; characters].- Seegers, 1997: 15, 22 [listed, photograph].   
 Differential diagnosis: Oryzias orthognathus is unique among ricefishes in having a lower jaw at an abrupt angle (nearly 90°) to the body axis; premaxilla correspondingly flat and extremely broad, with caniniform teeth in two irregular rows, outer teeth large and inner teeth fine, and no teeth on the medial portion of the premaxilla. Oryzias orthognathus differs from O. nigrimas, the other large (both reach over 50 mm SL), pelagic Oryzias in Lake Poso, by having 45–57, as opposed to 34–37, scales in a lateral series, seven, as opposed to six, pelvic-fin rays, and by lacking the distinctive sexual dichromatism of O. nigrimas.   
 Description: Elongate, maximum size of specimens examined 50.1 mm. Body slender, elongate, laterally compressed; body depth 17–22. No pronounced abdominal concavity between pelvic fins and anal fin. Mouth terminal, lower jaw at an abrupt angle (nearly 90°) to the body axis, and longer than upper jaw. Dorsal and ventral body profile nearly straight from head to dorsal- and anal-fin origins. Dorsal surface of head slightly convex between orbits. Head length 22–26; snout length 7–8; eye moderate, 8–9, orbits do not project beyond dorsal surface of head. Basal portion of dorsal and anal fin do not project significantly beyond primary body profile. Scales relatively small, cycloid and somewhat deciduous; 45–57 in a lateral series. Elongate, filamentous dorsal- and analfin rays in males; anal-fin rays without bony contact organs. Medialmost pelvic-fin ray connected to body via a membrane. Caudal fin slightly lunate, dorsal and ventral segmented caudal-fin rays longer than middle rays. Male with a short, slightly conical, tubular urogenital papilla; female with bilobed urogenital papilla.   
Premaxilla flat and extremely broad with distinct ascending process; caniniform teeth in two irregular rows, those in the outer row large and those in the inner row fine; no teeth on the medial portion of the premaxilla. No preethmoid cartilage; ossified portions of mesethmoid disc-shaped; anterior border of ethmoid cartilage irregular and may be indented anteriorly. No flanges on the ventral surface of the palatine and the quadrate. Dorsal ramus of hyomandibula not distinctly bifid, single cartilage articulates with sphenotic and pterotic. Lacrimal sensory canal carried in open bony groove. First pleural rib on parapophysis of third vertebra; first epipleural bone attaches to parapophysis of first vertebra dorsal to, and not in horizontal line with, posterior epipleural bones; lateral process of pelvic bone attaches to fourth or fifth pleural rib. Caudal skeleton with two epural bones; one ventral accessory bone. Procurrent caudalfin rays hooked at their base. Fifth ceratobranchial toothplates subtriangular, with pavement dentition anteriorly, followed by eight to nine discrete rows of unicuspid teeth, including a small, incomplete posterior row in the counterstained specimen of a female. Basihyal bone triangular, basihyal cartilage extremely elongate and rectangular. Epibranchial elements fully ossified; epibranchial 2 notably smaller than the other epibranchial elements.  
Dorsal-fin rays 8–11. Anal-fin rays 21–25. Pelvic-fin rays 7. Pectoral-fin rays 11–12. Principal caudal-fin rays i,4/5,i. Procurrent fin-rays, dorsal 5, ventral 6. Vertebrae 33 (13 + 20). Branchiostegal rays 5.  
 Cytogenetic data: Unknown.   
 Colour in life: Females golden brown on dorsal and lateral surfaces, whitish on belly. Males silvery grey on dorsal and lateral surfaces. Fins hyaline, except for caudal fin which has a yellow-orange dorsal and ventral margin, and one or two longitudinal purple lines on median rays (following Kottelat, 1990a: 56).   
 Colour in alcohol: Ground straw-coloured, belly pale whitish yellow. Dorsal surface of head and dorsal and lateral surface of body with dense dark brown to black chromatophores. A diffuse row of melanophores from the dorsal surface of the head to the dorsal-fin origin, an irregular, midlateral black line from the head to base of the caudal fin. Females with diffuse line of dark chromatophores dorsal from just posterior to anal-fin origin, along body just dorsal to anal-fin base to middle of caudal peduncle. Fins hyaline.   
 Distribution and habitat: A pelagic species endemic to Lake Poso, Sulawesi Tengah, Indonesia.   
 Remarks: The holotype, ZSM/LIPI 3 (50.0 mm), collected with the paratypes, below, was not examined by me. Data were augmented by those in Kottelat (1990a) and Uwa (1991b). Other common names for this species are pointed head medaka or pointed head ricefish (Seegers, 1997: 22).   
 Material examined: Thirty specimens (16.8–50.1 mm SL).   
Paratypes. INDONESIA. Sulawesi Tengah: Lake Poso, east shore between Tentena and Peura (field no. 88–26), M. Kottelat, 24–25.vi.1988, CMK 6362 (ex. CMK 6236) (female, 43.0 mm), counterstained, ZSM/ LIPI 4, 8 (17.2–50.1 mm).  
Non-type specimens. INDONESIA. Sulawesi Tengah: Lake Poso at Peura, eastern shore approx. 10 km S of Tentena, USNM 350562, 16 (16.8–46.5 mm, a male, 43.5 mm, and a female, 46.5 mm, of which have been cleared and counterstained), L. R. Parenti, K. D. Louie, P. Beta & boatmen, 13.viii.1995; Lake Poso, west bank of Poso R. where it empties into lake at Pamona Caves, USNM 350561, 5 (29.0– 43.6 mm), L. R. Parenti, K. D. Louie, P. Beta & boatmen, 13.viii.1995.
description: Published as part of Parenti, Lynne R., 2008, A phylogenetic analysis and taxonomic revision of ricefishes, Oryzias and relatives (Beloniformes, Adrianichthyidae), pp. 494-610 in Zoological Journal of the Linnean Society 154 (3) on pages 579-580, DOI: 10.1111/j.1096-3642.2008.00417.x, http://zenodo.org/record/5446868