Creagrutus phasma Myers 1927

Creagrutus phasma Myers, 1927

Creagrutus phasma Myers, 1927:117 [Venezuela, mouth of Curamuni (=Río Curamoni Rio Cassiquiare (=Río Casiquiare); see “Remarks,” below)].—Eigenmann and Myers, 1929:548 [based on Myers, 1927].—Mago-Leccia, 1971:9 [Venezuela, Río Casiquiare].—Fowler, 1975:27 [literature compilation].—Géry and Renno, 1989:3 [as possible senior synonym of Creagrutus bolivari].—Taphorn and Garcia Tenía, 1991:5 [Venezuela: Río Caroni].—Jepsen, 1997:454 [Venezuela, Río Cinaruco].

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, 5 teeth in the primary series of each premaxilla, 4 to 6 maxillary teeth, 6 or 7 teeth on each dentary, 8 or 9 predorsal median scales, 38 to 43 lateral line scales without a lamellar process over each pore, 2 post-anal median scales to the anal-fin origin, 4 scale rows between the dorsal-fin origin and the lateral line, 9 or 10 branched anal-fin rays, 5 to 8 gill rakers on the upper limb of the first gill arch and 9 to 12 gill rakers on the lower limb of the first gill arch, the distance from the dorsal-fin origin to the hypural joint (55.1%–60.3% of SL), the distance from the dorsal-fin origin to the anal-fin origin (27.4%–32.1% of SL), the distance from the dorsal-fin origin to the pelvic-fin insertion (20.0%–25.1% of SL), the caudal peduncle depth (9.0%–10.4% of SL), the dorsal-fin length (17.3%–22.1% of SL), the anal-fin length (13.7%–17.3% of SL), the snout length (25.3%–31.7% of HL), the near contact of the ventral margin of the third infraorbital and the horizontal limb of the preopercle, the presence of a distinct spot of dark pigmentation at the base of the middle caudal-fin rays, the prominent, anteriorly concave, crescent-shaped humeral mark without a secondary, dorsal patch of pigmentation, the absence of a distinct patch of pigmentation on the dorsal fin, and the lack of a series of dark spots along the midlateral surface of the body distinguishes Creagrutus phasma within the clade formed by Creagrutus and Piabina.

DESCRIPTION.—Morphometric and meristic data for Creagrutus phasma in Table 47. Body fusiform and slightly compressed laterally, compression accentuated in specimens less than approximately 50 mm SL. Greatest body depth at base of anteriormost ray of dorsal-fin. Dorsal profile of head distinctly convex from margin of upper lip to vertical through posterior margin of posterior nares, straight from that point to posterior tip of supraoccipital spine. Dorsal profile of body slightly convex from supraoccipital spine to origin of dorsal fin, straight from that point to anterior procurrent caudal-fin ray. Ventral profile of head variably developed, with obtuse angle approximately midway between margin of lower lip and posterior extremity of dentary, straight to slightly convex from that point to isthmus. Ventral profile of body slightly convex from isthmus to pelvic-fin insertion; straight from that point to anal-fin origin; straight to slightly concave from that point to caudal peduncle.

Anterior profile of head broadly rounded in lateral view. Upper jaw slightly longer than, and overhanging, lower jaw. Most external surfaces of ventral and ventrolateral portions of head covered with scattered, minute papillae. Anterior portion of snout relatively soft and fleshy, with concentration of soft tissues; minute papillae highly concentrated on snout and upper lip, continuing into mouth on fleshy flaps and plicae between outer and medial premaxillary teeth. Lower jaw distinctly fleshy anteriorly, with concentrated papillae, inner surfaces of lower lip convolute and papillose, with fleshy flaps extending into mouth.

Infraorbital series moderately well developed, with ventral margin of third infraorbital separated from ventral limb of preopercle by narrow gap in some specimens and with bones nearly in contact in other individuals. Posterior and ventral margins of third infraorbital usually forming broadly rounded obtuse angle, occasionally describing an arc and nearly concentric with orbit. Fourth infraorbital small and triangular, with its base at margin of orbit and apex directed posteriorly. Posterior margins of third through fifth infraorbitals narrowly separated from vertical limb of preopercle.

Premaxillary teeth in three distinct groups: primary row with 5 unicuspidate to tricuspidate teeth, anteriormost 3 premaxillary teeth often unicuspidate, without pronounced gap between first and second tooth of series; a medial, triangular cluster of 3 large tricuspidate teeth; and a single outer unicuspidate tooth positioned lateral to third or fourth tooth of primary tooth row. Maxilla with 4 to 6 tricuspidate teeth. Dentary usually with 6 or 7 usually tricuspidate teeth; first 2 teeth in dentary occasionally pentacuspidate, with minute outer pair of cusps. Two anteriormost dentary teeth largest and subequal, third tooth slightly smaller than second; remaining teeth in series distinctly smaller than 3 anterior teeth; third through sixth teeth slightly recurved.

Dorsal-fin rays ii,8 in all specimens. Dorsal-fin origin located slightly anterior to vertical through origin of pelvic fin. Distal margin of dorsal fin nearly straight or with very slight concavity as a result of elongation of second unbranched and anterior 2 or 3 branched rays. Anal-fin rays ii–iii,9–10. Mature males with anal-fin hooks, when present, on segments of first branched ray. Distal margin of anal fin slightly sigmoidal, with second unbranched and anterior 3 branched rays forming slightly elongate lobe, outline of posterior 5 or 6 rays concave. Pectoral-fin rays i, 11–13 (i, 11 in only 1 specimen). Pectoral fin short; tip reaching posteriorly, at most, to within 2 or 3 scale rows of pelvic-fin origin. Pelvic-fin rays i, 7–8 or i,6,i; typically i,7. Mature males, with pelvic-fin hooks, when present, on medial surfaces of segmented and unsegmented portions of main shaft and on medial, occasionally also on lateral, secondary branches of all rays medial of the lateral unbranched element. Tip of pelvic fin falling 2 or 3 scales short of anal-fin origin.

Posterior margin of body scales smoothly rounded to slightly undulate, latter condition especially developed ventrally and ventrolaterally.

Gill rakers 5–8 + 9–12.

COLORATION IN ALCOHOL.—Overall ground color straw to light brown, with pigment cells ranging from dark brown to sepia in most areas to nearly black in areas of concentrated pigmentation. Dorsal surface of head with diffuse pattern of small, light brown chromatophores; chromatophores most highly concentrated on median portion of upper lip and over snout. Dorsal surfaces of frontal and parietal portions of cranium densely pigmented with small, highly concentrated dark chromatophores over fontanelle, with larger, more scattered chromatophores present over other areas. Band of scattered, dark chromatophores extending from immediately lateral of nares posteroventrally and then continuing along ventral margin of orbit no further than midpoint of orbit. Infraorbitals posterior of orbit and dorsal one-half of opercle covered with numerous, scattered, small to large, dark chromatophores. Lower lip and ventrolateral surface of head unpigmented.

Body pigmentation diffuse, most concentrated dorsal of lateral line and in association with posteriormost exposed portions of scales. Scattered, dark chromatophores concentrated on dorsal portion of body between head and anterior of dorsal-fin base. Humeral mark usually in form of anteriorly concave crescent with dark pigmentation highly concentrated immediately dorsal of lateral line where more darkly pigmented area forms vertically elongate, rotund blotch within humeral mark. Humeral mark continuing dorsally from dark central portion of mark to within about 1 scale row of midline, with intensity of pigmentation decreasing dorsally. Humeral mark extending ventrally from central dark portion as less intensely pigmented, albeit continuous, field followed ventrally by scattered stellate chromatophores continuing to within about 1 scale row of medial pectoral-fin ray. Dark pigmentation of lateral surface of body ventral to lateral line, other than that associated with humeral bar, restricted to scattered, dark chromatophores outlining hypaxial myosepta immediately dorsal of anal-fin base and extending anteriorly to near pelvic-fin base. Faint midlateral body stripe associated with first and second scale rows dorsal of lateral line in some specimens, becoming denser and somewhat wider posteriorly and extending well ventral of lateral line on caudal peduncle.

Dorsal-fin membranes with dark chromatophores most concentrated on distal one-fourth to one-third of anterior 4 to 6 branched rays, unbranched rays distally pigmented; basal portions of shafts of all, or nearly all, fin rays with dark pigment. Anal fin mostly unpigmented; anterior surfaces of basal one-half of rays with dark pigment; several dark chromatophores scattered over rays and membranes of central portion of fin. Caudal fin with all fin rays delineated by dark pigment, pigmentation darkest on middle fin rays and giving appearance of elongate black spot. Pelvic fin hyaline. Pectoral fin unpigmented except for several isolated dark chromatophores associated with membrane of medial fin rays.

DISTRIBUTION.—Creagrutus phasma ranges from the upper portion of the Rio Negro in Brazil, north to various localities in the Río Orinoco basin in both Venezuela and Colombia (Figure 74, filled stars).

MATERIAL EXAMINED.—67 specimens (20, 42.2–68.4).

VENEZUELA. Amazonas: Río Casiquiare, mouth of Curamuni (=Río Curamoni, approximately 2°37′N, 66°12′W; see “Remarks” under species account), CAS 44210, 1 (50.2, lectotype of Creagrutus phasma; formerly IU 17681, in part); CAS 209191, 1 (47.2, paralectotype of Creagrutus phasma; formerly IU 17681, in part). Río Orinoco at playa approximately 0.5 km above La Esmeralda (3°09′N, 65°32′W), ANSP 161241, 7. Playa and backwater of Río Casiquiare, approximately 2.0 km downstream from mouth of Río Pamoni (2°48′N, 65°57′W), ANSP 161243, 6 (1, 43.9). Río Mavaca, beaches above base camp, Tapirapeco Expedition, MBUCV V-17823, 2. Caño entering into a laguna of Río Mavaca (2°17′22″N, 65°06′28″W), MCNG 28855, 1 (68.4). Apure: Río Cinaruco, near mouth (approximately 6°39′N, 67°07′W), MCNG 17961, 24 (7, 42.2–51.1). Bolivar: Sand bar along Río Mato (7°02′N, 65°13′W), ANSP 139598, 11. Pools and beaches in front of Salto de Icutu, Río Nichare system, Río Caura basin (5°53′00″N, 64°51′00″W), MCNG 21491, 10 (9, 42.6–63.4). Río Caura basin, island slightly below mouth of Río Nichare (6°30′N, 64°39′30″W), MCNG 21936, 1.

BRAZIL. Amazonas: Rio Negro, rapids at São Gabriel (0°08′S, 67°05′W), ANSP 150050, 1.

COLOMBIA. Meta:, Río Yucao River, 13.5 km SW of Puerto Gaitan (latter locality at 4°19′N, 72°04′W), UF 33527, 2.