Geophagus dicrozoster , Hernan López-Fernández & Donald C. Taphorn, 2004
treatment provided by
(Figs. 2a, 6-9)
Holotype. MCNG 40996, 193.0 mm SL; Venezuela: Apure: Río Cinaruco: Laguna Larga (6.5339°N 67.4150°W); D.A. Arrington and J. Arrington, 13 April 1999.
Paratypes. MCNG 30020, 7, 44.8-138.0 mm SL; Venezuela: Bolívar: Río Caroní: Campamento Guri; J.D.Williams and K.M. Ryan, 14 April 1994 . - AMNH 233636 (exMCNG40853), 1, 154.0 mm SL; Venezuela: Apure: Río Cinaruco: Laguna Oheros; D.A. Arrington and J. Arrington, 12 April 1999 . - MCNG 40311, 22, 12.2-84.6 mm SL (2 measured); Venezuela: Apure: Rio Cinaruco: Laguna Guayaba (6.5897°N 67.2400°W); D.A. Arrington and J. Arrington, 16 March 1999 . - AMNH 233635 (ex-MCNG 47603), 5, 109.6-178.0 mm SL; Venezuela: Apure: Río Cinaruco: Laguna Larga (6.5339°N 67.4150°W); K. Winemiller, H. López-Fernández, A. Arlington, L. Kelso-Winemiller, H. López-Chirico and J. Arlington, 1- 3 Jan 1999 . - MCNG 47604, 4, 177.0-202.0 mm SL; Venezuela: Apure: Río Cinaruco .
Diagnosis. A preopercular mark distinguishes Geophagus dicrozoster ZBK n. sp. from G. grammepareius ZBK , G. taeniopareius ZBK , G. argyrostictus ZBK and G. harreri ZBK , which have a complete infraorbital stripe (Fig. 1), and from G. abalios ZBK n. sp., G. brokopondo ZBK , G. surinamensis , G. megasema ZBK , G. camopiensis ZBK , and G. altifrons ZBK , which lack head markings. Preserved specimens of G. dicrozoster ZBK can be distinguished from other species with preopercular mark by the possession of seven vertical, parallel lateral bars, as opposite to G. winemilleri ZBK n. sp. (4 bars) and G. brachybranchus ZBK and G. proximus (no bars) (Fig. 2).
Description. Based on holotype (193.0 mm SL) and the 19 paratypes 63.4-202.0 mm SL with notes on variation among smaller specimens. Measurements and counts are summarized in Table 1. Sexes appear to be isomorphic.
Shape. Moderately elongate; dorsal outline more convex than ventral outline; head broader ventrally than dorsally; specimens 63.4 mm SL and smaller more elongate; interorbital area moderately concave. Dorsal head profile moderately convex, ascending to dorsal-fin origin, except in front of orbit where slightly concave, in specimens smaller than 65.0 mm SL, straight from orbit to dorsal-fin origin; dorsal-fin base descending, arched to last ray, then forming a horizontal, moderately concave line to caudal-fin insertion. Ventral head profile straight, slightly descending to chest; slightly convex to pelvic-fin insertion; straight, horizontal from pelvic-fin insertion to origin of anal fin; anal-fin base slightly convex, ascending; ventral caudal peduncle moderately concave, slightly ascending or horizontal in specimens 64.0 mm SL and smaller. Lips moderately wide, lower with slightly caudally expanded fold (see Kullander et al., 1992, Fig. 3). Maxilla reaching 1/3- 2/3 of the distance between nostril and orbit; ascending premaxillary process reaching slightly above midline of orbit. Opercule, preopercule, cleithrum, postcleithrum, and posttemporal lacking serration.
Scales. E1 34(3), 35(7), 36(8), 38(2); scales between upper lateral line and dorsal fin 6.5-8.5 anteriorly, 2.5-3.5 posteriorly. Scales between lateral lines 2. Scales on upper lateral line 19(1), 20(7), 21(8), 22(4) and lower lateral line 14(1), 15(4), 16(3), 17(9), 18(3). Anterior half of cheek naked, remainder with ctenoid scales; cheek scale rows 9-10. Opercule covered with ctenoid scales. Caudo-ventral area of subopercule naked, remainder with ctenoid scales. Interopercule with cycloid scales caudally. Single postorbital column of ctenoid scales, particularly in largest specimens. Occipital and flank scales ctenoid. Circumpeduncular scale rows 7-9 above upper, 9-11 below lower lateral line, ctenoid.
Fin scales. Anal, pectoral and pelvic fins naked. Dorsal fin scaled on spinous and soft portions, scales ctenoid, and arranged in double or triple columns along interradial membranes up to one third to one half of fin height. Scaly pad at base of dorsal formed by irregularly arranged small, ctenoid scales extending from first spine to third to seventh soft ray. Anal scaleless, scaly pad on base of anal absent, at most a few small scales on base of anterior portion of fin, moderately ctenoid. Caudal fin scaled along its entire surface, except the tip of rays, and part of membranes between D3 and V3, scales ctenoid. Accessory caudal fin extension of lateral line between V4-V5, absent on dorsal lobe.
Fins. Dorsal XVI-12(2), XVI-13(1), XVII-11(2), XVII-12(9), XVII-13(1), XVIII- 11(2), XVIII-12(2); anal III-7(1), III-8(18), III-9(1). Dorsal-fin spines increasing in length from first to sixth, equal length to ninth, then slightly shorter; lappets pointed, short; soft portion round, reaching just beyond caudal-fin insertion; moderately pointed in a 202.0 mm SL, and reaching about a third of caudal-fin length; rays 4-6 longest but not produced into filaments; in specimens 63.0 mm SL and smaller dorsal fin not reaching caudal-fin insertion. Anal fin round, moderately pointed in largest specimens, with rays 2-5 longest, not reaching caudal fin or barely beyond its base in largest specimens. Caudal fin emarginate with lobes of approximately the same length and without filaments; one specimen 120.2 mm SL with slightly produced ray D8. Pectoral fin elongate, more or less triangular, longest at 4th ray, reaching 1st or 2nd anal-fin spines, then progressively shorter ventrally. Pelvic fin triangular, first ray produced into a filament reaching 3rd anal-fin soft ray; in a specimen 202.0 mm SL almost reaching caudal-fin insertion; specimens 45.5 mm SL or less with slightly or not produced rays, reaching at most 1st anal-fin spine.
Teeth. Outer row of upper jaw with 17-26 approximately cylindrical, frequently blunt, slightly recurved, unicuspid teeth; larger than in inner rows, extending along most of premaxillary length; 6-7 inner rows, separated by a clear gap from outer row; teeth on inner row thin, slightly recurved unicuspids, forming a pad. Outer row of lower jaw with 16-22 blunt, slightly recurved unicuspid teeth; median 3 teeth more labially positioned than rest of row; inner rows 6 (4 in small specimens), forming a pad, separated from outer row by distinct gap; teeth thin, slightly recurved unicuspids.
Gills. External rakers on first gill arch; 10(11), 11(1) on epibranchial lobe, 1 in angle and 12(3), 13(7), 14(2) on ceratobranchial, none on hypobranchial. Microbranchiospines on the outer face of second to fourth arches. Gill filaments with narrow basal skin cover.
Tooth plates. Lower pharyngeal tooth plate elongate (Fig. 8); width of bone 80-82% of length; dentigerous area 80% of width; 28 teeth in posterior row, 11 in median row. Anteriormost teeth subconical, laterally compressed and erect; cusps posterior, slightly curved rostrad, small rostral edge ridge; lateral marginal teeth with same cusp pattern, teeth thinner and more laterally compressed towards caudal edge of plate; posteromedial teeth much larger, almost cylindrical, cusps posterior, almost blunt. Ceratobranchial 4 with 5 toothplates with 4-6, 5-7, 5-13, 6-11 and 3-7 teeth; one of two specimens with 7 toothplates with 6, 4, 5, 5, 4, 3 and 3 teeth on left side.
Vertebrae. 14+18=32(1), 14+19=33(10), 15+18=33(3), 15+19=34(1); 11-12 epihemal ribs.
Color pattern in alcohol (Fig. 6). Background color grayish yellow; nape, snout, upper lip and naked portion of cheek darker gray, scaled portion of cheek lighter; lower lip yellowish white. Vertical, blackish mark in the corner of the preopercule, continued into the interopercule as a faint spot; indistinguishable or faded in specimens smaller than 65.0 mm SL. Opercule with a dark, brown spot on dorsal edge, reaching first scale of upper lateral line, otherwise uniformly dusky yellow or silvery white in some specimens probably depending on preservation. Ventrally, gill cover dusky yellow or yellowish white in some specimens; branchiostegal membrane also yellowish, grayish brown in one specimen 202.0 mm SL. Chest yellow laterally and ventrally, white in many specimens, juveniles with distinctive silvery-white chest region; in best preserved specimens dusky yellow or white extends ventrally to base of caudal fin and to H3 on caudal peduncle flanks. Flanks with 7, dorso-ventrally directed, dark-gray bars fading or disappearing ventrally (Fig. 2a). Bar 1 expands from the 7th -8th predorsal scale to the base of the dorsal fin between spines 4-5 forming an inverted triangle; its anterior edge roughly delimited by the extrascapular and its posterior edge descending ventrally to the pectoral-fin insertion. Bar 2 extends between the base of dorsal-fin spines 6-7 and 9, and runs vertically to H6-7. Bar 3 extends between the base of dorsal-fin spines 10-11 and 12-13, descends ventrally and slightly caudally oriented, fading progressively to H6-7. A well-demarked, black medial spot is located on bar 3, extending rostro-caudally between scales 11 and 14-15 of E3 and dorso-ventrally between the lower half of E4 and E1, such that the upper lateral line traverses the dorsal 1/4-1/3 of the spot. Bar 4 extends between the bases of dorsal-fin spines 14-15 to 17, and descends ventro-caudally to the upper lateral line, where it merges with bar 5 such that the two bars form a “Y” shaped figure (Fig. 2a); in specimens 50.0 mm SL or less, bar 4 may appear as a spot on the base of the dorsal, not quite reaching bar 5. Bar 5 extends between the base of dorsal-fin spine 18 and ray 1 or rays 1-2 and rays 4- 5, it descends vertically fading at H1-2. Bar 6 extends from the base of the 7-8 dorsal fin rays to the second postdorsal scale in the caudal peduncle, descends vertically and fades at H1-2. Bar 7 covers the area between the last 4-5 lower lateral line scales and the base of the caudal fin, disappearing ventrally at H2.
Dorsal fin dusky, lappets dark gray or blackish, forming a faint dark edge along fin; dorsal fin immaculate except a few indistinct whitish spots in the membranes of caudal half of soft portion; in specimens 63.0 mm SL or smaller, three dusky longitudinal, parallel stripes alternate with light stripes along soft portion of dorsal fin. Anal fin hyaline to slightly dusky; 4 longitudinal, parallel gray bands along soft portion; largest specimen with dark gray lappets. Caudal fin gray-brown, with whitish longitudinal bands of variable length and elongate spots, forming no evident pattern; specimens up to 85.0 mm SL with 4 dark, vertical bands that gradually turn into the above described pattern with increasing size. Pectoral fin immaculate. Pelvic fin dusky, darker distally; spine and first ray whitish gray to dusky.
Live colors (Fig. 7). Dark markings as in alcohol specimens. Background color yellowish olive green; head silvery with yellow on gill cover, snout gray, upper lip iridescent blue extending behind lips to preopercular mark. Dorsal fin reddish with faint iridescent blue spots, especially on the soft portion; some specimens with proximal third of spiny portion yellow, probably due to breeding condition; anal fin red or reddish with distinctive iridescent blue horizontal banding; caudal fin reddish with a variable pattern of iridescent blue stripes and spots. Five to seven faint, yellow horizontal stripes alternating with olive green along body, but not always distinct.
Distribution and habitat (Fig. 9). Geophagus dicrozoster ZBK is common in the black waters of the Caura and Caroní drainages of the Guyana Shield; it is also present in all major tributaries of the middle and upper Orinoco, including the drainages of the Cataniapo, Ventuari, Atabapo, Ocamo, and Mavaca, as well as the Casiquiare and the headwaters of the Río Negro. In the llanos, G. dicrozoster ZBK is restricted to the moderately blackwatered Río Cinaruco, although further collections will likely show its presence in the nearby Río Capanaparo and its tributaries. No specimens have been captured from white water, or from llanos clear water drainages as the Aguaro-Guariquito.
Etymology. From the Greek dikros, forked, and zoster, belt. Given in reference to the “Y” formed by lateral bars 4 and 5. To be regarded as an adjective in masculine form.
USA, New York, New York, American Museum of Natural History
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