Creagrutus britskii Vari & Harold 2001

Creagrutus britskii

DIAGNOSIS.—The combination of the possession of premaxillary dentition arranged in the three components generalized for most of the species of Creagrutus and Piabina without a distinctly larger gap between the first and second teeth of the primary series, 2 or 3 teeth on the maxilla, typically 6 teeth in the primary series on the premaxilla, 4 or 5 teeth on each dentary, 36 to 39 lateral line scales without a lamellar process over each pore, 9 to 11 predorsal median scales, 5 scales rows between the dorsal-fin origin and the lateral line, 9 to 11 branched anal-fin rays, 36 or 37 vertebrae, the 6 or 7 gill rakers on the upper and 10 to 12 gill rakers on the lower limb of the first gill arch, the distance from the dorsal-fin origin to the pelvic-fin insertion (25.4%–32.6% of SL), the postorbital head length (38.1%–45.6% of HL), the snout length (28.3%–33.3% of HL), the interorbital width (30.3%–34.1% of HL), the depth of the caudal peduncle (11.4%–13.9% of SL), the well-developed third infraorbital with the ventral margin of its anterior portion contacting the preopercle in larger specimens, the moderately vertically elongate humeral mark not in the form a ventrally tapering vertical bar and lacking a distinct extension ventrally or a secondary patch of pigmentation dorsal to the primary mark, the lack of a series of dark spots along the midlateral surface of the body, and the lack of a discrete patch of dark pigmentation on the middle portion of the anterior dorsal-fin rays distinguish C. britskii from the other species in the clade composed of Creagrutus and Piabina.

DESCRIPTION.—Morphometric and meristic data for Creagrutus britskii in Table 11. Head relatively robust. Body proportionally moderately more elongate in smaller individuals, progressively more robust anteriorly with increasing body size. Greatest body depth at, or barely anterior to, dorsal-fin origin in individuals up to approximately 45 mm SL, shifted anteriorly in most larger specimens, particularly those with distended abdomens. Dorsal profile of head distinctly convex from margin of upper lip to vertical through posterior nostril, straight from that point to tip of supraoccipital spine in all specimens larger than 20 mm SL. Interorbital region gently convex. Predorsal profile of body continuing that of posterior portion of head and nearly straight to dorsal-fin origin in specimens up to approximately 35 mm SL, becoming progressively more convex in larger individuals. Predorsal region of body in preserved specimens transversely flattened anteriorly in all specimens larger than 20 mm SL, transversely flattened region extending nearly to dorsal-fin origin in smaller specimens, limited to anterior one-half of predorsal region in larger specimens that, in turn, have medial middorsal ridge along posterior one-third of predorsal region. Ventral profile of head gently convex overall anteriorly, with barely apparent obtuse angle at anteroventral corner of dentary, nearly straight from that region to isthmus. Ventral profile of body nearly straight up to approximately 35 mm SL, increasingly convex in larger individuals.

Characters A B

Morphometrics

Standard length 52.5 27.3–47.5

1. Snout to anal-fin origin 67.9 59.6–68.1

2. Snout to pelvic-fin insertion 47.2 43.3–52.3

3. Snout to pectoral-fin insertion 26.3 22.9–27.2

4. Snout to dorsal-fin origin 51.4 45.1–52.0

5. Dorsal-fin origin to hypural joint 52.6 52.1–58.0

6. Dorsal-fin origin to anal-fin origin 35.5 28.2–36.0

7. Dorsal-fin origin to pelvic-fin insertion 30.9 25.4–32.6

8. Dorsal-fin origin to pectoral-fin insertion 35.0 30.1–35.8

9. Caudal peduncle depth 13.3 11.4–13.9

10. Pectoral-fin length 22.4 17.1–22.4

11. Pelvic-fin length 18.7 13.7–17.9

12. Dorsal-fin length 24.8 20.5–24.8

13. Anal-fin length 18.7 17.0–20.2

14. Head length 27.5 23.7–27.5

15. Postorbital head length 45.2 38.1–45.6

16. Snout length 31.3 28.3–33.3

17. Bony orbital diameter 35.4 30.1–38.2

18. Interorbital width 32.6 30.3–34.1

Meristics

Lateral line scales 38 36–39

Scale rows between dorsal-fin origin and lateral line 5 5

Scale rows between anal-fin origin and lateral line 3 3–4

Predorsal median scales 11 9–11

Branched dorsal-fin rays 8 8

Branched anal-fin rays 9 9–11

Branched pelvic-fin rays 6 6

Pectoral-fin rays 13 11–13

Vertebrae 36 36–37

Head obtusely pointed in lateral view, more compressed laterally in dorsal view. Upper jaw longer than, and overhanging, lower jaw. Snout fleshy anteroventrally, with scattered papillae proximate to margin of upper lip. Lateral surface of upper lip with scattered papillae. Ventral margin of upper lip and fleshy folds and plicae extending between outer and medial premaxillary teeth with numerous papillae. Lower lip very fleshy with numerous papillae along anterodorsal margin and scattered papillae anteroventrally.

Infraorbital series moderately developed. Anterior portion of ventral margin of third infraorbital falling distinctly short of horizontal limb of preopercle in smaller specimens, progressively approaching that bone ontogenetically, and in contact with that portion of the preopercle in larger individuals. Posterior margins of third through fifth infraorbitals falling distinctly short of vertical limb of preopercle.

Premaxillary dentition in three series: primary row curved or very slightly sigmoid, typically with 6 teeth (only 5 teeth present on one premaxilla in one examined specimen) without pronounced gap between first and second tooth of series; triangular cluster of 3 larger teeth with posterolateral tooth largest and medial teeth of contralateral clusters in contact; and single tooth of form similar to that of primary series lying lateral to fourth tooth of primary premaxillary tooth row, or lateral to region of contact of fourth and fifth teeth. Maxilla with 2 or 3 tricuspidate teeth. Dentary with 4 or 5 teeth, anterior three teeth largest; first and second subequal and distinctly larger than third tooth; latter, in turn, notably larger than fourth tooth. Teeth all tricuspidate (when 4 teeth present) or last tooth conical, or nearly so (when 5 teeth present).

Dorsal-fin rays typically ii,8, rarely iii,8 (in only 3 examined specimens). Dorsal-fin origin at, to slightly posterior of, vertical through pelvic-fin insertion. Profile of distal margin of dorsal fin slightly concave. Anal-fin rays ii,9–11. Profile of distal margin of anal fin slightly concave. Mature males with many hooks on at least first and second branched anal-fin rays, some specimens with few hooks also present on third branched anal-fin ray. Pectoral-fin rays i, 10–12. Tip of pectoral fin falling distinctly short of pelvic-fin insertion in smaller individuals, extending to, or occasionally surpassing, that point in largest individuals. Pelvic-fin rays i,6,i in all examined specimens. Tip of pelvic fin extending posteriorly to anus or anal-fin insertion. Mature males with hooks on all branched pelvic-fin rays.

Gill rakers 6–7 + 10–12.

COLORATION IN ALCOHOL.—Overall ground coloration of relatively recently collected specimens tan. Dorsal surface of head with scattered surface chromatophores posteriorly, with chromatophore field becoming denser anteriorly, particularly over snout. Field of deep-lying, dark chromatophores on membranes overlying brain, chromatophore field most intense posterior of epiphyseal bar, degree of intensity of overall pigmentation variable between individuals. Region anterior to nostrils with crescent-shaped field of denser chromatophores sometimes continuous with narrow band of chromatophores along ventral and posterior margins of orbit. Region posterior of orbit with scattered chromatophores on infraorbitals and opercle.

Scales of posterodorsal portion of body with marginal series of dark chromatophores separated from basal patch of chromatophores by hyaline region. Pigmentation more intense anteriorly in smaller specimens and darker overall in larger individuals. Humeral mark vertically elongate, pigmentation most intense in central portion of mark. Central region sometimes expanded horizontally compared with remainder of mark. Dorsal portion of mark less intensely pigmented, with nearly vertical margins, or more often slightly arching anteriorly. Dorsal portion of mark merging into overall darker pigmentation of dorsal portion of body. Ventral portion of humeral mark below intensely pigmented region tapering ventrally. Midlateral stripe formed mostly by deep-lying, dark chromatophores; stripe extending posteriorly from slightly behind humeral mark to caudal peduncle, most obvious on posterior two-thirds of body.

Dorsal fin with last unbranched and first branched rays often outlined with dark chromatophores. Distal portions of membranes between anterior branched rays with scattered, large, dark chromatophores. Anterior two-thirds of branched anal-fin rays outlined basally by dark pigmentation; pigmentation extending further along rays on anterior rays. Caudal-fin rays, particularly central, dorsalmost, and ventralmost rays outlined by dark chromatophores. Basal portions of middle rays with diffuse concentration of darker chromatophores, giving appearance of indistinct spot in some specimens. Pectoral and pelvic fins hyaline.

ETYMOLOGY.—The species name, britskii, is in honor of Heraldo Britski, Museu de Zoologia of the Universidade de São Paulo, Brazil, in recognition of his many contributions to our understanding of South American freshwater fishes and of his assistance to the senior author over the years.

ECOLOGY.—Two of the paratype lots of Creagrutus britskii (USNM 292226, 292214) were collected in small upland rivers, 6–25 m in width, with bottoms formed by rubble, gravel, bedrock, and silt. Turbidity was moderate, and current ranged from slow to swift.

DISTRIBUTION.—Creagrutus britskii is known only from the southeastern portions of the Rio Tocantins basin (Figure 28, triangles).

MATERIAL EXAMINED.—126 specimens (57, 27.3–52.5).

HOLOTYPE.—BRAZIL. Goiás: Iaciara, Ribeirão Macambira (approximately 14°20′S, 46°45′W), near bridge on highway GO 112, collected by J.C. de Oliveira and W.J.M. Costa, 14 Sep 1988, MZUSP 40537, 1 (52.5).

PARATYPES.—56 specimens (56, 27.3–47.5).

BRAZIL. Goiás: Iaciara, Ribeirão Macambira (approximately 14°20′S, 46°45′W), near bridge on highway GO 112, collected with holotype, MZUSP 50540, 12 (33.7–43.5); USNM 340952, 4 (34.8–42.7; 2 specimens cleared and counterstained for cartilage and bone). Iaciara, Rio Prata above bridge on highway GO 112 (approximately 14°20′S, 46°45′W), collected by J.C. de Oliveira and W.J.M. Costa, 14 Sep 1988, MZUSP 46546, 18 (31.2–41.0). Rio Tocantins basin, Ribeirão Cangalha, at road, 14 air km NNE of Formosa (15°24′S, 47°17′W), collected by W.C. Starnes et al., 13 Nov 1984, USNM 292214, 3 (42.4–46.8). Ribeirão Paranoa do Meio, at road crossing, 11 air km NNE of Formosa (approximately 15°25′S, 47°18′W), collected by W.C. Starnes et al., 13 Nov 1984, USNM 292226, 13 (27.3–46.6). Minaçu, tributary of Córrego Lageado, left bank tributary of Rio Tocantins, along road to Porto Rubião (approximately 13°38′S, 48°19′W), collected by D.F. Moraes, Jr. et al., 16 Jan 1988, MNRJ 13048, 6 (39.9–47.5).

NONTYPE SPECIMENS.—69 specimens.

BRAZIL. Goiás: Ribeirão Angélicu, above entrance to Caverna da Angélicu, São Domingos (approximately 13°36′S, 46°24′W), MZUSP 40629, 2. Município de Monte Alegre de Goiás, Rio Bezerra, right bank tributary of Río Paraná, MZUSP 40702, 3. Iaciara, Ribeirão Macambira (approximately 14°20′S, 46°45′W), near bridge on highway GO 112, MZUSP 50541, 63 (collected with holotype); MZUSP 40534, 1.