Creagrutus petilus Vari & Harold 2001

Creagrutus petilus, USNM 340957, 2, 44.0–44.4 mm, paratypes; Brazil, Rondônia, Rio Marco Rondon

Creagrutus phasma, MCNG 21491, 1, 51.4 mm; Venezuela, Bolivar, Salto de Icutu, Río Caura system. MCNG 17961, 2, 40.5–46.2 mm; Venezuela, Apure, Río Cinaruco.

Creagrutus petilus

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, 6 teeth in the primary tooth row of the premaxilla, 5 dentary teeth, 37 to 39 lateral line scales without a lamellar process over each pore, 9 or 10 predorsal median scales, 4 scale rows between the dorsal-fin origin and the lateral line, 36 to 39 vertebrae, 10 or 11 branched anal-fin rays, 2 post-anal median scales to the anal-fin origin, 5 or 6 gill rakers on the upper limb of the first gill arch and 9 to 11 gill rakers on the lower limb of the first gill arch, the distance from the snout to the anal-fin origin (61.5%–65.6% of SL), the distance from the snout to the pelvic-fin insertion (46.5%–50.0% of SL), the distance from the snout to the pectoral-fin insertion (24.5%–27.5% of SL), the distance from the dorsal-fin origin to the anal-fin origin (26.5%–29.6% of SL), the distance from the dorsal-fin origin to the pelvic-fin insertion (22.1%–26.1% of SL), the distance from the dorsal-fin origin to the pectoral-fin insertion (28.5%—31.9% of SL), the caudal peduncle depth (9.4%–10.8% of SL), the head length (26.6%–27.7% of SL), the postorbital head length (40.7%–45.3% of HL), the bony orbital diameter (34.0%–40.1% of HL), the snout length (27.0%–31.4% of HL), the interorbital width (26.0%–30.5% of HL), the moderately developed third infraorbital, which does not contact the horizontal limb of the preopercle, the lack of a series of dark midlateral spots on the body, the vertically elongate humeral mark with variable anterior and posterior margins, the lack of a distinct spot of pigmentation on the basal portions of the middle caudal-fin rays, and the absence of a discrete patch of dark pigmentation on the middle portion of the anterior dorsal-fin rays distinguishes Creagrutus petilus within the clade composed of Creagrutus and Piabina.

DESCRIPTION.—Morphometric and meristic data for Creagrutus petilus in Table 46. Head relatively robust, body relatively slender but transversely robust, more so in larger individuals. Greatest body depth at vertical through dorsal-fin origin in smaller individuals, shifted somewhat anterior of that point in larger examined specimens, particularly individuals with distended abdomens. Dorsal profile of head distinctly convex from margin of upper lip to vertical through anterior margin of orbit, nearly straight from that point to tip of supraoccipital spine in smaller specimens, slightly convex in larger individuals. Predorsal profile of body straight to slightly convex, but without distinct change in alignment relative to profile of head common to many congeners. Predorsal portion of body without median ridge. Ventral profile of head convex anteriorly, with variably developed, but obvious, obtuse angle at anteroventral corner of dentary, approximately straight from that angle to isthmus. Prepelvic profile of body slightly convex, more so in larger specimens, particularly those with distended abdomens. Prepelvic region of body obtusely flattened transversely.

Characters A B

Morphometrics

Standard length 42.9 29.8–48.8

1. Snout to anal-fin origin 65.3 61.5–65.6

2. Snout to pelvic-fin insertion 49.2 46.5–50.0

3. Snout to pectoral-fin insertion 27.0 24.5–27.5

4. Snout to dorsal-fin origin 46.2 45.3–49.3

5. Dorsal-fin origin to hypural joint 53.2 53.0–56.9

6. Dorsal-fin origin to anal-fin origin 29.6 26.5–29.5

7. Dorsal-fin origin to pelvic-fin insertion 23.1 22.1–26.1

8. Dorsal-fin origin to pectoral-fin insertion 30.5 28.5–31.9

9. Caudal peduncle depth 10.5 9.4–10.8

10. Pectoral-fin length 18.2 18.0–21.1

11. Pelvic-fin length 14.9 13.4–16.4

12. Dorsal-fin length 20.3 20.2–25.1

13. Anal-fin length 17.7 17.3–19.0

14. Head length 26.6 26.7–27.7

15. Postorbital head length 43.0 40.7–45.3

16. Snout length 30.7 27.0–31.4

17. Bony orbital diameter 35.1 34.0–40.1

18. Interorbital width 26.3 26.0–30.5

Meristics

Lateral line scales 39 37–39

Scale rows between dorsal-fin origin and lateral line 4 4

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

Predorsal median scales 10 9–10

Branched dorsal-fin rays 8 8

Branched anal-fin rays 11 10–11

Branched pelvic-fin rays 6 6

Pectoral-fin rays 12 11–12

Vertebrae 37 36–39

Head obtusely flattened in both lateral and dorsal views. Upper jaw distinctly longer than, and overhanging, lower jaw. Snout slightly fleshy anteromedially, with numerous papillae anteriorly and on plicae and folds extending between outer and medial premaxillary teeth. Scattered papillae present on lateral surface of anterior portion of maxilla. Lower lip fleshy, particularly anteriorly, with numerous papillae along dorsal margin and few scattered papillae anteromedially.

. Infraorbital series moderately developed. Third infraorbital horizontally elongate, ventral margin of infraorbital ranging from falling distinctly short of horizontal limb of preopercle to approaching, but not contacting, that bone. Posterior margins of third through fifth infraorbitals falling distinctly short of vertical limb of preopercle.

Premaxillary dentition in three series: primary row distinctly sigmoid, consisting of 6 teeth without pronounced gap between first and second tooth of series but with medial tooth widely separated from its contralateral partner by gap filled by fleshy folds; triangular cluster of 3 larger teeth; and single tooth of form similar to that of primary series lying lateral to fourth tooth of primary premaxillary series. Maxilla with 2 or 3 tricuspidate teeth. Dentary with 5 tricuspidate teeth; first and second dentary teeth distinctly larger than other teeth, second tooth slightly larger than first tooth and about 1.5 times height of third tooth; fourth and fifth teeth distinctly smaller than third tooth and compressed.

Dorsal-fin rays ii,8 in all specimens. Dorsal-fin origin approximately at, or slightly anterior to, vertical through pelvic-fin insertion. Profile of distal margin of dorsal fin ranging from straight to slightly concave. Anal-fin rays ii, 10–11. Profile of distal margin of anal fin slightly concave. Hooks present on first, or first and second, branched anal-fin rays in mature males. Pectoral-fin rays i, 10–11. Tip of pectoral fin extending posteriorly to pelvic-fin insertion in some individuals, falling slightly short of that point in other, typically larger, specimens. Pelvic-fin rays i,6,i in all specimens. Tip of pelvic fin extending posteriorly to, or nearly to, anus in smaller individuals, fin typically shorter in larger specimens. Hooks present on all branched pelvic-fin rays of mature males.

Gill rakers 5–6 + 9–11.

COLORATION IN ALCOHOL.—Ground coloration of specimens tan. Dorsal surface of head with few scattered, dark, surface chromatophores anteriorly, over snout, and on anterior portion of upper jaw. Chromatophore field somewhat more concentrated in larger individuals. Dorsal surface of head otherwise without surface pigmentation. Series of very dark, stellate chromatophores on membranes overlying posterior portion of brain. Anterior portion of brain overlain by contralateral, horizontally elongate patches of dark chromatophores. Region anterior to nostrils with indistinct, crescent-shaped patch of dark chromatophores; patch more obvious in smaller individuals that have little other dark pigmentation on snout. Region anteroventral to orbit, with scattered, dark chromatophores; chromatophores not concentrated into distinct stripe as in some congeners. No distinct band of dark chromatophores along ventral and posterior margins of orbit. Dorsal portion of infraorbital series and proximate portion of opercle with scattered, dark chromatophores.

Scales of anterodorsal portion of body with crescent-shaped patch of dark chromatophores over center of exposed field and with irregular series of chromatophores along distal margin of scale. Two regions of chromatophores on each scale separated by hyaline area. Humeral mark prominent, more obvious in larger specimens. Mark vertically elongate, proportionally more so in larger individuals, extending ventrally approximately one-half scale beyond lateral line. Anterior and posterior margins of humeral mark variable in form, mark generally wider midway along its vertical extent. Larger specimens often with anterodorsally arched region of less intense chromatophores extending from dorsal portion of primary body of mark. Diffuse midlateral stripe formed of deep-lying, dark chromatophores and extending varying distances along body. Stripe in smaller individuals barely apparent, beginning under dorsal fin and extending posteriorly onto base of caudal fin. Stripe becoming more prominent, longer, and wider with increasing body size. Largest examined specimens with midlateral stripe extending from region anterior to humeral mark, through mark, and posteriorly to caudal-fin base. Body stripe continuous posteriorly with horizontal stripe on middle caudal-fin rays.

Dorsal fin with basal portions of fin rays outlined by dark chromatophores in medium-sized and larger examined specimens. Anterior margin of second unbranched dorsal-fin ray often outlined by dark chromatophores with distal membranes of branched rays having scattered chromatophores, particularly in larger specimens. Anal fin with basal portions of rays, particularly anterior and middle rays, outlined by chromatophores, chromatophore field extending varying degrees distally on some anterior branched rays. Caudal fin in smaller individuals with few scattered, dark chromatophores on basal portions of middle rays. Chromatophore field on caudal fin expanding progressively with increasing body size. Dark chromatophores forming distinct horizontal stripe over middle rays of caudal-fin, stripe most intense basally, giving appearance of basal spot in some individuals. Rays of dorsal and ventral portions of fin variably outlined by dark chromatophores, giving those portions of fin dusky appearance. Pectoral and pelvic fins hyaline or with few scattered, dark chromatophores.

ETYMOLOGY.—The specific name, petilus, from the Latin for thin or slender, refers to the relatively elongate body form of this species.

ECOLOGY.—It appears that the largest mature males (33.2–37.2 mm SL) (maturity indicated by the presence of hooks on the anal and pelvic fins) in the single available large population sample of Creagrutus petilus (MNRJ 13370, MNRJ 14807, USNM 340957) are consistently smaller than the largest females (36.7–48.8 mm SL).

Stomach contents of two specimens cleared and counterstained for this study consisted mostly of chopped seeds with occasional insect parts. One of the cleared and stained specimens, collected in late July, had ovaries with well-developed eggs.

DISTRIBUTION.—Creagrutus petilus is only known from the upper portion of the Rio Machado, a right bank tributary of the Rio Madeira in Rondônia, Brazil (Figure 74, triangles).

COMPARISONS.—In addition to C. petilus, only one Creagrutus species, C. anary, is known from the central portions of the Rio Madeira basin. The two species are readily distinguishable in overall appearance, numbers of lateral line scales, and in their relative head lengths, snout lengths, and interorbital widths (Tables 5, 46).

MATERIAL EXAMINED.—25 specimens (22, 29.8–48.8).

HOLOTYPE.—BRAZIL. Rondônia: Rio Marco Rondon, Pimenta Bueno (approximately 11°29′S, 61°12′W), collected by G.W. Nunan and W.D. Bandeira, 17 Jul 1986, MNRJ 14807, 1 (42.9).

PARATYPES.—21 specimens (21, 29.8–48.8).

BRAZIL. Rondônia: Rio Marco Rondon, Pimenta Bueno (approximately 11°29′S, 61°12′W), collected with holotype, MNRJ 13370, 12 (31.5–45.5); USNM 340957, 8 (29.8–44.5; 2 specimens cleared and counterstained for cartilage and bone). Rio Mariape, Ouro Preto do Oeste (approximately 10°40′S, 62°18′W), collected by G.W. Nunan and W.D. Bandeira, 15 Jul 1986, MNRJ 13368, 1 (48.8).

NONTYPE SPECIMENS.—3 specimens.

BRAZIL. Rondônia: Igarapé at Riozinho (approximately 11°30′S, 61°18′W), MNRJ 13369, 1. Rio Boa Vista, Ouro Preto do Oeste, along highway BR 364 to Nova União (approximately 10°40′S, 62°18′W), MNRJ 13371, 2.