Creagrutus ephippiatus Vari & Harold 2001

Creagrutus ephippiatus

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, 6, occasionally 5, teeth in the primary series of each premaxilla, 3 or 4 maxillary teeth, 6, less commonly 7, teeth on each dentary, 10 to 12 predorsal median scales, 38 to 41 lateral line scales without a lamellar process over each pore, 4, rarely 5, scale rows between the dorsal-fin origin and the lateral line, 3 or 4 scale rows between the anal-fin origin and the lateral line, 10 or 11 branched anal-fin rays, 38 to 40 vertebrae, 6 or 7 gill rakers on the upper limb and 11 or 12 gill rakers on the lower limb of the first gill arch, the caudal peduncle depth (10.7%–12.0% of SL), the distance from the dorsal-fin origin to the anal-fin origin (27.8%–29.7% of SL), the distance from the dorsal-fin origin to the pelvic-fin insertion (23.1%–25.7% of SL), the distance from the dorsal-fin origin to the pectoral-fin insertion (30.7%–33.6% of SL), the postorbital head length (43.7%–47.4% of HL), the interorbital width (29.7%–33.7% of HL), the contact between the ventral margin of the third infraorbital and the horizontal limb of the preopercle in larger specimens, the spot of dark pigmentation at the base of the middle caudal-fin rays, the vertically elongate, ventrally attenuating humeral mark extending to the middorsal line, without a secondary, dorsal patch of pigmentation, the absence of a distinct patch of pigmentation on the dorsal fin, the dark pigmentation on the basal portions of the middle caudal-fin rays, and the lack of a series of dark spots along the midlateral surface of the body distinguishes Creagrutus ephippiatus within the clade formed by Creagrutus and Piabina.

Characters A B

Morphometrics

Standard length 47.6 27.4–58.4

1. Snout to anal-fin origin 60.7 60.5–64.5

2. Snout to pelvic-fin insertion 45.3 44.3–48.0

3. Snout to pectoral-fin insertion 22.5 22.8–24.7

4. Snout to dorsal-fin origin 46.9 46.8–49.8

5. Dorsal-fin origin to hypural joint 55.9 54.0–57.9

6. Dorsal-fin origin to anal-fin origin 28.6 27.8–29.7

7. Dorsal-fin origin to pelvic-fin insertion 25.4 23.1–25.7

8. Dorsal-fin origin to pectoral-fin insertion 32.4 30.7–33.6

9. Caudal peduncle depth 11.3 10.7–12.0

10. Pectoral-fin length 20.2 18.1–21.3

11. Pelvic-fin length 16.4 14.0–16.7

12. Dorsal-fin length 22.1 19.5–22.4

13. Anal-fin length 16.8 15.5–18.5

14. Head length 25.6 24.3–27.0

15. Postorbital head length 44.3 43.7–47.4

16. Snout length 28.7 27.3–31.6

17. Bony orbital diameter 33.6 31.3–35.7

18. Interorbital width 30.3 29.7–33.7

Meristics

Lateral line scales 39 38–411

Scale rows between dorsal-fin origin and lateral line 4 4–52

Scale rows between anal-fin origin and lateral line 3 3–43

Predorsal median scales 10 10–12

Branched dorsal-fin rays 8 8

Branched anal-fin rays 11 10–11

Branched pelvic-fin rays 7 5–74

Pectoral-fin rays 12 11–13

Vertebrae 38 38–405

1Forty-two lateral line scales present in only 1 specimen.

2Five scale rows between dorsal-fin origin and lateral line present in only 3 paratypes.

3Four scale rows between anal-fin origin and lateral line present in only 2 paratypes.

4Five branched pelvic-fin rays present in only 1 paratype; 7 branched rays present only in larger paratypes.

5Forty vertebrate present in only 1 paratype.

DESCRIPTION.—Morphometric and meristic data for Creagrutus ephippiatus in Table 17. Head and body moderately robust, more so in anterior portion of body in larger specimens. Greatest body depth at, to slightly anterior of, dorsal-fin origin. Dorsal profile of head distinctly convex from margin of upper lip to vertical through posterior nostril, slightly convex from that point to tip of supraoccipital spine; convexity in this region less pronounced in larger individuals. Interorbital region transversely rounded. Dorsal profile of body slightly convex from tip of supraoccipital spine to dorsal-fin origin, but without distinct change in alignment relative to dorsal profile of head. Dorsal surface of body with obtuse middorsal ridge; ridge more obvious posteriorly. Ventral profile of head with obtuse angle at anteroventral corner of dentary, angle variably obvious; profile slightly convex from angle to isthmus. Prepelvic profile of body slightly convex in smaller individuals, somewhat more convex in some larger specimens. Prepelvic region of body transversely rounded.

Head obtusely pointed in lateral view, somewhat more compressed in dorsal view. Upper jaw somewhat longer than, and overhanging, lower jaw. Anterior of snout, particularly anteromedial portion with numerous papillae. Papillae more concentrated on fleshy upper lip, especially along ventral lip margin and on folds and plicae extending between outer and medial premaxillary teeth. Lower lip with numerous papillae on dorsal surface and scattered papillae anteriorly.

Infraorbital series well developed in all specimens larger than about 30 mm SL, with ventral margin of third infraorbital falling slightly short of horizontal limb of preopercle in smaller specimens, but contacting that bone in larger individuals. Posterior margins of third through fifth infraorbitals distinctly separated from vertical limb of preopercle in all specimens; gap decreasing proportionally ontogenetically, but still distinct in larger individuals.

Premaxillary dentition in three series: primary series sigmoid, with 6, occasionally 5, tricuspidate teeth, without pronounced gap between first and second tooth of series but with medial tooth separated from matching tooth of contralateral series by distinct gap; triangular cluster of 3 teeth, larger than those of primary series; and single tooth of form similar to that of primary series occurring lateral to fourth tooth of primary series or in the region slightly anterolateral to area of contact of third and fourth teeth of primary premaxillary row. Maxilla with 3 or 4 tricuspidate teeth, 3 teeth typically present in smaller individuals. Dentary with 6, less commonly 7, tricuspidate teeth, with seventh tooth, when present, having barely apparent cusps; second tooth more massive than and about one-fourth longer than first tooth; second tooth about 1.5 times as high as third tooth; third tooth twice as high as fourth tooth; fourth through sixth or seventh teeth progressively smaller.

Dorsal-fin rays ii,8 in all specimens. Dorsal-fin origin approximately at vertical through pelvic-fin insertion. Profile of distal margin of dorsal fin slightly concave. Anal-fin rays iii,10–11 or ii,10. Profile of distal margin of anal fin concave. Mature males with hooks on distal margins of first 4 or 5 branched anal-fin rays, and occasionally on last unbranched ray; number of hooks decreasing posteriorly and progressively limited to increasingly more distal portions of fin ray. Pectoral-fin rays i,10–12, typically i,11. Tip of pectoral fin falling 1 to 2 scales short of pelvic-fin insertion. Pelvic-fin rays i,5–6,i or i,7; typically i,6,i; i,7 in some larger specimens. Tip of pelvic fin falling 1 to 2 scales short of anal-fin origin. Mature males with hooks on all branched pelvic-fin rays, including medial ray, if branched, and sometimes on medial ray when unbranched; hooks, when present on medial unbranched ray, usually less dense than those on branched rays.

Gill rakers 6–7–12.

COLORATION IN ALCOHOL.—Ground coloration tan. Dorsal surface of head in smallest specimens with dense pigmentation overlying brain and scattered, dark chromatophores on snout. Specimens greater than 30 mm SL with entire dorsal surface of head covered with dense field of small, dark chromatophores extending anteriorly to margin of upper lip and posteriorly to anterior margin of orbit. Density of chromatophore field somewhat less on upper lip in some individuals. Region anterior to nostrils with pigmentation somewhat more intense, forming distinct crescent-shaped patch in smaller specimens; patch not apparent in medium-sized to larger individuals. Smaller individuals with narrow band of dark pigmentation extending from under nostrils to region anteroventral or ventral of orbit; band subsumed into overall darker pigmentation in that region in larger specimens. Region posterior to orbit along with dorsal portion of opercle with scattered, dark chromatophores in smaller specimens, chromatophore field expanding further ventrally and somewhat more dense, especially along posterior margin of orbit in larger individuals.

Scales of posterolateral surface of body with series of dark chromatophores along posterior margin in smaller individuals; chromatophore field becoming progressively wider in larger individuals, but with basal portions of scales lacking chromatophores and forming regular pattern of lighter colored regions. Humeral mark obvious and vertically elongate in specimens of all sizes. Mark comma-shaped and limited to lateral portion of body in smaller individuals, midlaterally centered main body darkest with anterior arching patch of more diffuse dark chromatophores extending dorsally from its dorsal portion of dorsal midline. Contralateral humeral marks meet middorsally and form horizontally elongate dark middorsal stripe that extends about 3 scales along predorsal region; stripe extending approximately one scale posterior of margin of humeral mark. Main portion of mark becoming more intensely pigmented and vertically elongate with increasing size. Humeral mark extending ventrally by more diffuse, typically ventrally tapering patch of chromatophores; in largest specimens humeral mark extending to about one scale dorsal of horizontal through pectoral-fin insertion. Middorsal scales posterior to humeral marks with patches of dark pigmentation in larger specimens. Dark midlateral stripe limited to posterior two-thirds of body, pigmentation more intense posteriorly. Midlateral stripe merging anteriorly into overall dark pigmentation on lateral surface of the body in larger individuals.

Dorsal fin with first unbranched ray and distal portions of second unbranched rays covered with dark stellate chromatophores. Membranes of all but one or two posteriormost branched fin rays with dispersed, dark, irregularly shaped chromatophores. Chromatophore field becoming progressive shorter on distal portions of successive fin membranes. Distal portion of second and third unbranched and first and sometimes second branched anal-fin rays unpigmented; otherwise fin rays outlined by small dark chromatophores, with scattered chromatophores on intervening portions of fin membranes. Middle caudal-fin rays more intensely pigmented than rest of fin, with remaining fin rays outlined, to varying degrees, by small dark chromatophores. Pectoral and pelvic fins hyaline, or with some scattered, small, dark chromatophores in larger specimens.

ETYMOLOGY.—The specific name, ephippiatus, from the Latin, ephippium, meaning saddle, refers to the saddle-like humeral marks that meet along the dorsal midline.

ECOLOGY.—One of the nontype lots (AMNH 93144) was collected on a small sandy beach over a sand and mud bottom with detritus. A second lot (AMNH 93147) was captured at the upper end of rapids in the Río Siapa over a gravel and boulder bottom.

COMPARISONS.—Creagrutus ephippiatus is somewhat similar to C. provenzanoi of the Río Cataniapo, a tributary of the upper Río Orinoco. The two species can, however, be distinguished on the basis of the more arcuate dorsal portion of the humeral mark that extends further dorsally in C. ephippiatus compared to the mark in C. provenzanoi, the number of rows of scales above the lateral line (4, rarely 5, in C. ephippiatus versus 5, rarely 4, in C. provenzanoi), and less discretely in the distance from the snout to the pectoral-fin insertion (22.5%–24.7% of SL versus 24.4%–27.3% of SL, respectively).

Creagrutus ephippiatus is rather similar in terms of overall meristics and morphometrics to C. magoi of the central portions of the Río Orinoco basin. The species differ, however, in overall body form that is best reflected in the distance from the dorsal-fin origin to the anal-fin origin (27.8%–29.7% of SL in C.ephippiatus versus 29.2%–33.8% of SL in C. magoi), details of dark pigmentation (form of humeral mark and pigmentation of middle caudal-fin rays). The species also have a pronounced modal shift in the number of total vertebrae (C. ephippiatus: 38 (34), 39(10), 40(1) versus C. magoi: 36(6), 37(38), 38(2)).

DISTRIBUTION.—Creagrutus ephippiatus is only known from the Río Siapa, a southern tributary of the Río Casiquiare, upper Río Negro basin, in southern Amazonas State, Venezuela (Figure 38, triangle), and is the only member of the genus known from that river system.

MATERIAL EXAMINED.—56 specimens (35, 27.4–58.4).

HOLOTYPE.—VENEZUELA. Amazonas: Upper Río Siapa, Campamento Siapa (Siapa Base Camp), collected by R. Royero et al., 26 Mar 1988, MBUCV V-29068, 1 (47.6).

PARATYPES.—34 specimens (34, 27.4–58.4).

VENEZUELA. Amazonas: Upper Río Siapa, Campamento Siapa (Siapa Base Camp), collected with holotype, MBUCV V-29069, 24 (27.4–51.0); MBUCV V-18623, 3 (33.9–58.4); USNM 355116, 7 (33.3–47.0; 2 specimens cleared and counterstained for cartilage and bone).

NONTYPE SPECIMENS.—21 specimens.

VENEZUELA. Amazonas: Upper Río Siapa, below Camp 1, MBUCV V-19187, 4. Upper Río Siapa, at Siapa Base Camp, small beach on right bank, AMNH 93144, 13. Upper Río Siapa, Yanomani Village, upper end of rapids on left bank, AMNH 93147, 4.