Comprehensive Description
(
Anglèis
)
fornì da Smithsonian Contributions to Zoology
Creagrutus molinus
DIAGNOSIS.—The elongate form of the head and body and, in particular, the unusual premaxillary dentition with only two of the three principal components of the premaxillary dentition generalized for the species of Creagrutus, the primary tooth row without a pronounced gap between the first and second teeth, and the posteromedial triangular cluster of three teeth, combined with the absence of the third component, the separate tooth lateral to the fourth tooth in the primary premaxillary tooth row distinguishes Creagrutus molinus from all other species in the clade consisting of Creagrutus and Piabina. In addition, the combination of the contact of the first and second teeth of the primary premaxillary series, 3 teeth on the maxilla, 6 teeth in the primary tooth row of the premaxilla, 41 lateral line scales without a lamellar process over each pore, 11 predorsal median scales, 4 scale rows between the dorsal-fin origin and the lateral line, 38 vertebrae, 12 branched anal-fin rays, 2 post-anal median scales to the anal-fin origin, 11 gill rakers on the lower limb of the first gill arch, the distance from the snout to the pectoral-fin insertion (24.7% of SL), the distance from the dorsal-fin origin to the anal-fin origin (26.0% of SL), the distance from dorsal-fin origin to the pectoral-fin insertion (27.8% of SL), the snout length (31.0% of SL), the postorbital head length (39.3% of HL), the well-developed third infraorbital ventrally contacting the horizontal limb of the preopercle, the lack of a series of dark midlateral spots on the body, the rotund, albeit indistinct, humeral mark, the absence of chevron-shaped marks on the body, and the absence of a discrete patch of dark pigmentation on the middle portion of the anterior dorsal-fin rays distinguishes Creagrutus molinus within the clade composed of Creagrutus and Piabina.
Characters Morphometrics
Standard length 55.8
1. Snout to anal-fin origin 63.4
2. Snout to pelvic-fin insertion 44.8
3. Snout to pectoral-fin insertion 24.7
4. Snout to dorsal-fin origin 45.3
5. Dorsal-fin origin to hypural joint 53.8
6. Dorsal-fin origin to anal-fin origin 26.0
7. Dorsal-fin origin to pelvic-fin insertion 21.5
8. Dorsal-fin origin to pectoral-fin insertion 27.8
9. Caudal peduncle depth 11.3
10. Pectoral-fin length 18.6
11. Pelvic-fin length 13.1
12. Dorsal-fin length 19.7
13. Anal-fin length 18.6
14. Head length 25.1
15. Postorbital head length 39.3
16. Snout length 31.0
17. Bony orbital diameter 33.6
18. Interorbital width 30.7
Meristics
Lateral line scales 41
Scale rows between dorsal-fin origin and lateral line 4
Scale rows between anal-fin origin and lateral line 3
Predorsal median scales 11
Branched dorsal-fin rays 8
Branched anal-fin rays 12
Branched pelvic-fin rays 6
Pectoral-fin rays 12
Vertebrae 38
DESCRIPTION.—Morphometric and meristic data for Creagrutus molinus in Table 37. Head and body elongate, much more so than in the majority of its congeners. Greatest body depth at dorsal-fin origin. Dorsal profile of head distinctly convex from margin of upper lip approximately to vertical through posterior nostril, nearly straight from that point to rear of supraoccipital spine. Predorsal profile of body slightly convex. Postdorsal profile of body nearly straight. Ventral profile of head and body gently convex from margin of upper lip to anal-fin origin. Obtuse angle at anteroventral corner of dentary obvious in most congeners not apparent in this species.
Head obtusely pointed in lateral and dorsal views. Upper jaw longer than, and overhanging, lower jaw. Anterior portion of snout fleshy, with numerous papillae over median region, upper lip, lateral surface of maxilla, and on plicae and folds extending between outer and medial premaxillary teeth. Lower lip thick and fleshy anteriorly, with numerous papillae along dorsal surface.
Infraorbital series moderately well developed. Ventral margin of third infraorbital contacting horizontal limb of preopercle. Posterior margins of third through fifth infraorbitals falling short of vertical limb of preopercle.
Premaxillary dentition of the holotype (the only known specimen) proportionally relatively massive on one side of head; premaxillary dentition in process of replacement on other side of head. Premaxilla with only two of three major components typically present in other Creagrutus species. Primary row of premaxillary dentition consisting of 6 distally rounded teeth, with brown-tipped central raised point, without pronounced gap between first and second tooth of series; 6 partially developed teeth in the process of replacement also apparent in main tooth row on right side. Single tooth, typically lateral to primary row of premaxillary teeth in Creagrutus species, absent, and no space apparent on premaxilla onto which tooth would have attached. No indication of single replacement tooth on side of premaxilla in which teeth are in process of replacement. Triangular cluster of median teeth formed by 3 massive rounded teeth with central raised point. Three worn maxillary teeth present. Dentary with 3 massive teeth anteriorly. Total number of dentary teeth indeterminable without forcing open lower jaw and potentially damaging the unique specimen.
Dorsal-fin rays ii,8. Dorsal fin located slightly anterior of vertical through pelvic-fin insertion. Profile of distal margin of dorsal fin straight. Anal-fin rays ii,12. Profile of distal margin of anal fin distinctly concave. Mature male holotype with paired hooks present on all but distal segments of first branched pelvic-fin rays and some, but not most, of distal segments of second branched ray. Hooks limited to main shaft and posterior branches of these rays. Pectoral-fin rays i, 11. Tip of pectoral fin extending posteriorly slightly more than three-fourths of distance to pelvic-fin insertion. Pelvic-fin rays i,6,i. Tip of pelvic fin extending posteriorly approximately three-fourths of distance to anal-fin origin. Mature males with hooks present on all branched anal-fin rays and on medial unbranched rays. Hooks distributed both on basal portion of ray and each segment, other than distalmost segment; limited to posterior margin of main shaft and posterior branch of branched rays except for medialmost ray having hooks on both branches.
Gill rakers 7 + 11.
COLORATION IN ALCOHOL.—Overall ground coloration yellowish, overlain midlaterally and on portions of head by guanine in single known specimen. Dorsal surface of head with field of small, dark chromatophores most concentrated over fontanelle. Chromatophore field denser over snout and upper lip. Region anterior to nares without dense concentration of chromatophores typical of many Creagrutus species. Region ventral of nares and along ventral margin of anterior portion of adipose eyelid with posteroventrally inclined band of small, dark chromatophores. Scattered, dark chromatophores over fourth and fifth infraorbitals and dorsal portion of opercle.
Body with scattered, dark chromatophores over dorsolateral and dorsal surface, more concentrated dorsally, with chromatophores denser along posterior region of scales in this region and forming dark, reticulate pattern. Humeral mark relatively faint, formed of small chromatophores arranged in irregularly rotund blotch; mark mostly located dorsal of lateral line. Faint midlateral stripe on posterior portion of caudal peduncle and on base of middle caudal-fin rays. Dorsal- and anal-fin rays outlined by scattered, small, dark chromatophores. Caudal-fin rays mostly delimited by small, dark, chromatophores, other than for basal portions of rays lying dorsal and ventral of middle rays of fin. Pectoral and pelvic fins mostly hyaline.
ETYMOLOGY.—The specific name, molinus, from the Latin for grinder, refers to the large teeth in the upper and lower jaws of this species.
DISTRIBUTION.—Creagrutus molinus is known only from the type locality in the upper Rio Araguaia basin (Figure 67, triangle).
COMPARISONS.—The distinctive premaxillary dentition characterized by large teeth limited to two of the three components typical for the species of Creagrutus, with a lack of the single tooth of form similar to that of primary series lateral to the primary tooth series, is unique to C. molinus in the genus. Within the greater Rio Tocantins drainage system, including the Rio Araguaia, C. molinus is distinguished from the other Creagrutus species of the basin by having 4 scales above the lateral line to the dorsal-fin origin (contrary to 5 in C. atrisignum and C. britskii), 12 branched anal-fin rays (contrary to 9 or 10 in C. figueiredoi and C. menezesi), 5 teeth in the primary premaxillary tooth row and 38 vertebrae (contrary to 6 teeth in the primary premaxillary tooth row and 35 or 36 vertebrae in C. mucipu), 9 to 11 gill rakers on the lower limb of the first arch and 41 lateral line scales (versus 13 or 14 rakers and 37 to 39 scales in C. saxatilis), and various proportional morphometric values (numbers 7, 8, 11 in C. seductus, compare Tables 37 and 53).
MATERIAL EXAMINED.—1 specimen (1, 55.8).
HOLOTYPE.—BRAZIL. Mato Grosso: Rio Araguaia basin, riacho (small stream) tributary to Ribeirão Lajeadinho, Município de Alto Araguaia (approximately 17°19′S, 53°12′W); collected by L.P.S. Portugal and F. Langeani, MZUSP 41461, 1 (55.8).
- sitassion bibliogràfica
- Vari, Richard P. 2001. "Phylogenetic study of the neotropical fish genera Creagrutus Günther and Piabina Reinhardt (Teleostei:Ostariophysi:Characiformes), with a revision of the cis-Andean species." Smithsonian Contributions to Zoology. 1-239. https://doi.org/10.5479/si.00810282.613
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