Creagrutus vexillapinnus Vari & Harold 2001

Creagrutus vexillapinnus

DIAGNOSIS.—The distinct patch of black pigmentation on the central portions of the posterior unbranched and anterior branched dorsal-fin rays autapomorphically distinguishes Creagrutus vexillapinnus from its congeners. In addition to this unique pigmentation pattern, 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, 6 dentary teeth, 39 to 41 lateral line scales without a lamellar process over each pore, 8 or 9 predorsal median scales 4 scale rows between the dorsal-fin origin and the lateral line, 37 to 39 vertebrae, 12 to 14 branched anal-fin rays, 2 post-anal median scales to the anal-fin origin, 6 to 8 gill rakers on the upper limb of the first gill arch, the distance from the dorsal-fin origin to the pelvic-fin origin (25.7%–30.9% of SL), the distance from the dorsal-fin origin to the anal-fin origin (29.3%–34.7% of SL), the distance from the snout to the pectoral-fin insertion (24.6%–27.5% of SL), the distance from the dorsal-fin origin to the pectoral-fin insertion (30.2%–33.5% of SL), the dorsal-fin length (17.3%–23.5% of SL), the postorbital head length (36.0%–42.5% of HL), the bony orbital diameter (35.7%–42.5% of HL), the well-developed third infraorbital with its ventral margin approaching, or contacting, the horizontal limb of the preopercle, the lack of a series of dark midlateral spots on the body, and the vertically elongate, slightly ventrally attenuating humeral mark with straight anterior and posterior margins distinguishes Creagrutus vexillapinnus within the clade composed of Creagrutus and Piabina.

DESCRIPTION.—Morphometric and meristic data for Creagrutus vexillapinnus in Table 57. Body relatively deep compared with many congeners, becoming proportionally deeper ontogenetically. Greatest body depth at dorsal-fin origin. Dorsal profile of head smoothly convex from margin of upper lip approximately to vertical through posterior nostril; degree of convexity greater in larger specimens. Head profile nearly straight from above posterior nostril to tip of supraoccipital spine. Interorbital region gently convex transversely. Predorsal profile of body of smaller individuals nearly straight and smoothly continuing profile of posterior portion of head; profile in larger individuals distinctly convex, with notable change in alignment relative to dorsal profile of head. Postdorsal profile of body nearly straight in specimens of all sizes. Ventral profile of head with rounded obtuse angle delimiting anteroventral angle of dentary and nearly straight from that angle to isthmus. Prepelvic profile convex; convexity more pronounced in larger individuals.

Head obtusely pointed in both lateral and dorsal views. Upper jaw longer than, and overhanging, lower jaw. Anterior portion of snout fleshy, more so in larger individuals, with field of scattered papillae anteromedially. Papillae more concentrated along upper and lower lips and on folds and plicae extending between outer and medial premaxillary teeth. Lower lip very fleshy, particularly anteriorly, with scattered papillae anteromedially.

Infraorbital series moderately well developed. Ventral margin of third infraorbital ranging from falling slightly short of, to being in contact with, horizontal limb of preopercle. Posterior margins of third through fifth infraorbitals falling short of vertical limb of preopercle; extent of gap between infraorbitals and preopercle decreasing progressively dorsally.

Premaxillary dentition in three series: primary row consisting of 6 teeth arranged in slight curve without pronounced gap between first and second teeth of series; cluster of 3 larger teeth with posterolateral tooth largest; and single tooth of form similar to that of primary series, lateral to fourth tooth of primary series. Maxilla with 2 or 3 tricuspidate teeth. Dentary with 6 teeth; anterior 3 teeth tricuspidate and distinctly larger than remaining teeth; first and second teeth distinctly larger than third tooth, with second tooth somewhat larger than first tooth. Fourth through sixth teeth graded in size; fourth and fifth teeth tricuspidate and sixth tooth conical.

Dorsal-fin rays ii,8. Dorsal-fin origin approximately at vertical through pelvic-fin insertion. Profile of distal margin of dorsal fin slightly concave in smaller individuals, concavity more pronounced in larger specimens. Anal-fin rays ii, 12–14 or iii, 13–14. Profile of distal anal-fin margin distinctly concave, with last unbranched and anterior 2 or 3 branched rays forming distinct lobe. Anterior 1 to 3 branched anal-fin rays in mature males with 1 or 2 bilaterally paired hooks. Hooks restricted to posterolateral surface of main shaft of ray. Pectoral-fin rays i,11–13. Tip of pectoral fin extending posteriorly nearly to pelvic-fin insertion in smaller specimens, falling distinctly short of that point in larger specimens. Pelvic-fin rays i,6,i in all specimens. Tip of pelvic fin extending posteriorly to anus in smaller specimens; falling somewhat short of that point in larger specimens. Mature males with pelvic-fin hooks, when present, located on both segmented and unsegmented portions of all branched rays; limited to medial branches of rays, with 1 or 2 hooks per segment.

Gill rakers 6–8 + 11–13.

COLORATION IN ALCOHOL.—Overall ground coloration light tan. Dorsal surface of head with scattered, small, dark, superficial chromatophores. Membranes overlying dorsal surface of brain covered by somewhat larger chromatophores in smaller specimens, these masked by thickened bones and connective tissue in adults. Concentration of dark surface chromatophores on dorsal surface of head greater anteriorly, but overall intensity of pigmentation not as pronounced as in many congeners. Chromatophores more concentrated anterior to nares, but not forming obvious crescent-shaped patch of dark pigmentation present in many Creagrutus species. Some irregularly situated dark chromatophores immediately ventral and posterior to orbit, but these, again, not forming distinct curved band present in many congeners. Fifth infraorbital and dorsal portion of opercle covered with scattered, dark chromatophores.

Dorsal and dorsolateral portions of body with field of scattered, dark chromatophores; posterior margin of scales in these areas with slightly denser series of chromatophores forming very faint reticulate pattern. Humeral mark faint, vertically elongate and variably attenuate ventrally. Humeral mark extending approximately 2 scales dorsal of lateral line and up to 1 scale ventral of lateral line.

Dorsal fin with distinct black patch extending across central portions of fin from membrane between first and second unbranched dorsal-fin rays posteriorly to membrane between fifth and sixth branched rays; dark pigmentation most intense on membranes but with portions of rays incorporated into patch partially overlain by dark chromatophores. Remaining portions of dorsal fin either hyaline or with scattered, dark chromatophores. Caudal fin with scattered chromatophores, some specimens with slightly greater concentration of dark chromatophores on basal portions of middle caudal-fin rays. Anal fin hyaline or with scattered, small, dark, chromatophores. Pectoral and pelvic fins hyaline.

ETYMOLOGY.—The specific name, vexillapinnus, from the Latin, vexillum, for flag, and pinna, fin, is in reference to the prominent black spot on the dorsal fin.

DISTRIBUTION.—Creagrutus vexillapinnus is known from the upper portions of the Rio Negro in Brazil and Venezuela and the upper portions of the Rio Orinoco in Venezuela (Figure 90, squares; see also comments under “Geographic Variation” following).

GEOGRAPHIC VARIATION.—The type series of Creagrutus vexillapinnus was collected at various localities along the upper Rio Negro within Brazil. In addition, two lots from the Río Orinoco basin (ANSP 162052, 6 specimens; MCNG 27888, 11 specimens), both consisting of specimens all smaller in body size than the type series, are apparently conspecific with C. vexillapinnus. Despite the small sample sizes, it is noteworthy that the Río Orinoco specimens tend to have modally fewer vertebrae (37, n=6; 38, n=11) than found in the samples of C. vexillapinnus from the Rio Negro (38, n=2; 39, n=4). The condition and relatively small body sizes of the specimens from the Río Orinoco makes it impossible, however, to take most counts and measurements with an accuracy comparable to those for the Rio Negro samples. The comparisons between the Río Orinoco sample and the Rio Negro specimens, nonetheless, show shifted, albeit overlapping, values in the relative length of the dorsal fin and the relative postorbital length (Table 57). Additional samples from intervening areas are necessary to determine whether these differences between the samples from the Rio Negro and Río Orinoco represent clinal variation or perhaps the existence of two species.

MATERIAL EXAMINED.—23 specimens (18, 28.1–50.4).

HOLOTYPE.—BRAZIL. Amazonas: Rio Negro, Cachoeira de São Gabriel (0°08′S, 67°05′W), collected by M. Goulding, 20 May 1979, MZUSP 29894, 1 (50.4).

PARATYPES.—5 specimens (5, 33.3–42.0).

BRAZIL. Amazonas: Rio Negro basin, Rio Marauiá, Cachoeira do Bicho-Açú (approximately 0°20′S, 65°20′W), collected by M. Goulding, 12 Dec 1979, MZUSP 29896, 1 (38.6); USNM 341360, 1 (33.6). Rio Negro basin, Rio Marauiá, Cachoeira do Bicho-Açú (approximately 0°20′S, 65°20′W), collected by M. Goulding, Oct 1979, MZUSP 31220, 1 (33.3). Rio Negro, praia de Urumari, above Barcelos (0°30′S, 63°30′W), collected by M. Goulding, 6 Dec 1979, MZUSP 29893, 1 (39.6); USNM 341361, 1 (42.0; specimen cleared and counterstained for cartilage and bone).

NONTYPE SPECIMENS.—17 specimens (12, 28.1–43.6).

VENEZUELA. Amazonas: main channel of Río Casiquiare, approximately 1.5 hr from its confluence with the Río Orinoco (3°05′N, 65°55′W), ANSP 162052, 6 (1, 29.0). Río Mavaca, Caño Huayapiwei (02°11′30″N, 65°06′W), MCNG 27888, 11 (28.1–43.6).