Characidium, Armbruster & Lujan & Bloom, 2021

Armbruster, Jonathan W., Lujan, Nathan K. & Bloom, Devin D., 2021, Redescription of the Guiana Shield Darter Species Characidium crandellii and C. declivirostre (Crenuchidae) with Descriptions of Two New Species, Ichthyology & Herpetology 109 (1), pp. 102-122 : 120

KEY TO SPECIES OF THE FAST-WATER CHARACIDIUM OF THE GUIANA SHIELD

1a. Twelve circumpeduncular scales. Dorsal fin falcate with a medial dark band and terminal white band ( Figs. 4 , 5 ). Origin of adipose fin centered at vertical above insertion of posteriormost anal-fin ray ( Figs. 4 , 5 ). Pectoral fin uniformly dark or peripherally dark with lighter center. Proximal dentary and

premaxillary teeth wide and tri- to pentacuspid (central cusp longest) _________ Characidium crandellii

1b. Ten circumpeduncular scales. Dorsal fin only slightly concave along distal margin and with two or more thin dark bands ( Figs. 7 , 8 , 10–12 ). Origin of adipose fin at vertical over center of anal-fin base or more anterior. Pectoral fin light with at least one (usually two or three) dark bands made of separate elongate spots ( Figs. 7 , 8 , 10–12 ). Proximal dentary and premaxillary teeth narrow, peg-like, tricuspid, but only central cusp conspicuous ___________________________________ 2

2a. Pelvic fin with two unbranched rays. Pectoral fin with four unbranched rays ( Fig. 1B ) _________________________________ _____________________________________________ C. duplicatum , new species

2b. Pelvic fin with one unbranched ray. Pectoral fin with three unbranched rays ( Fig. 1A ) ______________________________ 3

3a. Dorsal coloration consisting of prominent saddles that extend to a faint midlateral stripe that may appear as a series of blotches (stripe most prominent in preserved specimens). No accessory bars between saddles. Ventral portion of sides with few, rectangular to square blotches that do not extend dorsal to midlateral stripe ( Figs. 7 , 8 ) _________________ C. declivirostre

3b. Dorsal saddles not prominent in adults, and usually confluent with thin bands from below midlateral stripe, which is usually demarcated by a faint stripe made of zig-zag lines with the stripe most prominent in smaller individuals. Thin bars also present in lighter interspaces between saddles, some of which extend below midlateral stripe ( Figs. 11 , 12 ). Ventral portion of sides with numerous narrow bars that extend above midlateral stripe (in juveniles, only some bars may continue dorsal to midlateral stripe; Figs. 11 , 12 ) ____ C. wangyapoik , new species

Figures

FIG. 4. Dorsal, lateral, and ventral views of Characidium crandellii in life, potential nuptial male, AUM 67142, 106.9 mm SL; Ireng River population. Photos by N. K. Lujan.

FIG. 5. Dorsal and lateral views of Characidium crandellii in life, common coloration, AUM 62874, 57.0 mm SL; Kuribrong River population. Photos by J. W. Armbruster.

FIG. 7. Dorsal, lateral, and ventral views of Characidium declivirostre in life, AUM 56680, 55.5 mm SL; Raudales Danto, Río Cuao, Amazonas, Venezuela. Photos by N. K. Lujan.

FIG. 8. Dorsal, lateral, and ventral views of a specimen of Characidium declivirostre from the same stream as the type locality, AUM 36625, 50.1 mm SL. Scale ¼ 1 cm. Photos by J. W. Armbruster.

FIG. 10. Lateral view (top) of Characidium duplicatum, new species, in life and dorsal, lateral, and ventral views after preservation, CSBD F-3614, holotype, 39.4 mm SL. Photos by J. W. Armbruster.

FIG. 11. Dorsal, lateral, and ventral views of Characidium wangyapoik, new species, in life, CSBD F-3615, holotype, 72.6 mm SL. Photos by N. K. Lujan.

FIG. 12. Dorsal, lateral, and ventral views of Characidium wangyapoik, new species, after preservation, CSBD F-3615, holotype, 72.6 mm SL; Kuribrong River population. Photos by J. W. Armbruster.

FIG. 1. Thickened, keratinized pads on the undersurface of the anterior pectoral-fin rays of (A) Characidium wangyapoik, new species, CSBD F-3615, holotype, and (B) C. crandellii, AUM 67142. Photos by N. K. Lujan.