Characidium wangyapoik, 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 : 117-120

Characidium wangyapoik , new species

urn:lsid:zoobank.org:act:1EBB34BE-431E-4D03-A343-6E8132EE810C

Figures 1A , 11–12

Characidium n. sp. ‘Ireng’.— Lujan et al., 2020: 1216 [locality information].

Holotype.— CSBD F-3615 (ex AUM 67118 ), 1 (1mo/me, 1gm), 72.6 mm SL, Guyana (border with Brazil), Potaro-Siparuni (Region 8), Amazon River basin, Ireng River, first shoal upriver from split with Sukwabi Creek, 5.07711, –59.97423, N. K. Lujan, J. W. Armbruster, D. C. Werneke, M. Ram, 8 January 2016.

Paratypes.— All specimens Guyana (border with Brazil), Potaro-Siparuni ( Region 8), Amazon River basin, Ireng River basin (known as the Rio Mau in Brazil) : ANSP 207526 , 3 (1mo/me, 3gm), 42.6–56.8 mm SL , AUM 67036 , 26 (5mo/ me, 26gm, 4cs), 22.0– 59.9 mm SL , CSBD F-3616 , 3 (1mo/me, 3gm), 37.7–52.2 mm SL , INPA ICT-059496 , 3 (0mo/me, 3gm), 52.6–54.6 mm SL , ROM 111286 , 3 (0mo/me, 3gm), 47.7–53.8 mm SL, Ireng River , at Orinduik Falls, between upper and lower falls, 4.72536, –60.03852, D. C. Werneke, J. W. Armbruster, N. K. Lujan, M. Ram, 2 January 2016 ; AUM 67046 , 16 (0), 17.8–46.4 mm SL, Ireng River , below lower Orinduik Falls, 4.71898, –60.03507, N. K. Lujan, J. W. Armbruster, D. C. Werneke, M. Ram, 3 January 2016 ; AUM 67068 , 18 (0), 25.2–43.5 mm SL, Ireng River , at Branana Rapids, shoals downstream of Orinduik Falls, 4.67585, –60.06046, D. C. Werneke, J. W. Armbruster, D. I. Brooks, M. Ram, 4 January 2016 ; AUM 67076 , 4 (0), 36.0– 40.4 mm SL, Ireng River , at Orinduik Falls, between upper and lower falls, 4.72536, –60.03852, D. C. Werneke, J. W. Armbruster, D. I. Brooks, M. Ram, N. K. Lujan, 4 January 2016 ; AUM 67077 , 20 (0mo/me, 13gm), 31.8–51.9 mm SL, Ireng River , at Orinduik Falls, around halfway between upper and lower falls, 4.72176, –60.03703, D. C. Werneke, J. W. Armbruster, D. I. Brooks, M. Ram, N. K. Lujan, 4 January 2016 ; AUM 67094 , 1 (0), 30.2 mm SL, Ireng River , just above Orinduik Falls, 4.72798, –60.03597, N. K. Lujan, J. W. Armbruster, D. C. Werneke, D. I. Brooks, M. Ram, 5 January 2016 ; AUM 67118 , 14 (4mo/me, 7gm, 2cs), 49.4–76.1 mm SL , INPA ICT-059497 , 2 (1mo/me, 2gm), 60.6–62.6 mm SL, first shoal upriver from split with Sukwabi Creek , 5.07711, –59.97423, N. K. Lujan, J. W. Armbruster, D. C. Werneke, M. Ram, 8 January 2016 ; AUM 67143 , 6 (0mo/me, 6gm), 44.8–67.7 mm SL, Ireng River , shoals at mouth of Monkey Creek, Kaibarupai, 5.04398, –59.97717, N. K. Lujan, J. W. Armbruster, D. C. Werneke, 9 January 2016 ; AUM 67181 , 9 (3mo/me, 9gm), 49.1–68.8 mm SL , ROM 111287 , 2 (2mo/me, 2gm), 60.6–61.3 mm SL, Ireng River , shoals at mouth of Monkey Creek, Kaibarupai, 5.04398, –59.97717, J. W. Armbruster, N. K. Lujan, D. I. Brooks, 12 January 2016 ; AUM 67189 , 2 (0mo/ me, 2gm), Sukwabi Creek , East Fork, downstream of Wotowanda Falls, 5.08867, –59.96952, J. W. Armbruster, N. K. Lujan, D. I. Brooks, D. C. Werneke, P. Peters , R. Daniel , local fishermen, 13 January 2016 ; AUM 67196 , 12 (0mo/me, 11gm), 28.1–67.9 mm SL, Ireng River , downstream of Kaibarupai, 5.02404, –59.97763, D. C. Werneke, J. W. Armbruster, N. K. Lujan, M. Ram, D. I. Brooks, 14 January 2016 ; AUM 67199 , 2 (0), 19.7–23.2 mm SL, Ireng River , at Sand Hill shoals, 4.96554, –59.99411, D. C. Werneke, J. W. Armbruster, N. K. Lujan, M. Ram, D. I. Brooks, 14 January 2016 ; AUM 67204 , 12 (5mo/me), 17.1–72.0 mm SL, Ireng River , at Waipa Landing, 4.93345, –59.99514, D. C. Werneke, J. W. Armbruster, N. K. Lujan, M. Ram, D. I. Brooks, 14 January 2016 .

Diagnosis.— Characidium wangyapoik can be distinguished from all crenuchids except C. crandellii , C. declivirostre , and C. duplicatum by having venter without scales from the isthmus to the pelvic girdle (vs. maximally to pectoral insertion) and from most species of Characidium by having a very large pectoral fin with first three unbranched pectoral-fin rays thickened and first pectoral-fin ray bent at an oblique angle (vs. pectoral-fin rays not thickened and first pectoral-fin ray either straight or slightly convex). Characidium wangyapoik differs from C. crandellii , C. declivirostre , and C. duplicatum by having at least the ventral region of flank with thin bars becoming contiguous across body at larger sizes (vs. ventral area with almost square blotches), having lateral-line canal in most of scales very short (~ 25% of scale length), and having canal pores covered by preceding scales (vs. canal at least 33% of scale length and pores not covered by preceding scales); from C. crandellii by having 10 circumpeduncular scales (vs. 12), having two or more thin dark bands consisting of spots on rays in dorsal and pectoral fins (vs. a median wide dark band with pigment concentrated on membranes in dorsal fin and pectoral fin either entirely dark or dark with lighter middle), having an almost square dorsal fin with slightly concave distal margin (vs. falcate), having adipose fin located above middle of anal-fin base (vs. anterior edge of adipose fin at or behind vertical through posteriormost anal-fin insertion), by having dentary and premaxillary teeth narrow, peg-like, and maximally tricuspid with only central cusp well developed (vs. wide and tri- to pentacuspid, central cusp longest), by having zero to two (total) teeth in second dentary row (vs. 8 or more); by a preanal length/SL ratio of 77.4–82.3% (vs. 72.9–76.6%), and anal–apex length/SL ratio of 94.6–100.3% (vs. 89.4–94.0%); from C. declivirostre by having the flanks with 10 or more narrow bars (vs. less than 10 almost square blotches); and from C. duplicatum by having one leading unbranched pelvic ray (vs. two). Characidium wangyapoik is most similar in color to C. amaila from the upper Kuribrong River, but it has bands in the dorsal and pectoral fins (vs. no bands in C. amaila ) and the unbranched pectoral-fin rays are greatly thickened (vs. only slightly thickened).

Description.— Measurements based on 21 specimens ( Table 2 ); meristics based on 20 specimens (reported below). Dorsal profile of body forms convex arc from tip of snout to posterior end of supraoccipital, then becomes steeper and longer convex arc from supraoccipital to end of dorsal fin (highest point of arc at dorsal-fin origin); dorsal profile relatively straight and ventrally angled from dorsal fin to adipose fin, then forming concave arc to caudal fin. Ventral profile straight to anal fin, then forming concave arc to caudal fin. Body depth greatest at dorsal origin and least at middle of caudal peduncle. Body oval in cross section anteriorly (flattened ventrally) and oval with dorsal and ventral surfaces somewhat flattened on caudal peduncle. Eye diameter 52.5–69.0% snout length, decreasing in size with SL ( Fig. 3 ), oval, angled with anterior vertex ventral to posterior vertex; dorsal rim of orbit slightly higher than interorbital surface. Snout broadly rounded. Gill membranes united across isthmus. Tubercles present in both sexes dorsally on head and anterodorsal scales.

Scales cycloid with most scales having 10–30 short, parallel striae (most on first postdorsal scale). Lateral line complete with canal occupying approximately 1/4 of scale length and pores covered by previous scales; 30 (1), 31 (4), 32 (12), or 33 (3) lateral-line scales; lateral-line scales distinctly smaller anteriorly; naked area between anterior lateral-line scales and pectoral-fin base; lateral line continues onto scales covering caudal base. 4 scales above lateral line and 2 scales below lateral line; 10 circumpeduncular scales. Scales covering anterior 1/5 of caudal fin. 7 (2), 8 (14), or 9 (4) predorsal scales. Venter unscaled on isthmus and posteriorly to 4 to 5 scales anterior to pelvic-fin origin.

Dorsal fin with 2 unbranched and 8 (1) or 9 (19) branched rays (ii,8–9); first unbranched ray about 1/3 length of second; first unbranched ray longest and last shortest; fin roughly rectangular. Pectoral fin with 3 unbranched and 10 (19) or 11 (1) branched rays (iii,10–11); unbranched rays and first branched ray with thick pads of tissue anteriorly; first unbranched ray strongly curved; first branched ray longest and last shortest; pectoral fin oriented obliquely on body with posteriormost insertion located posterodorsally to origin. Pelvic fin with 1 leading unbranched ray, 6 (19) or 7 (1) branched rays, and 1 posterior unbranched ray (i,6–7,i); first branched ray longest; 2 to 3 pelvic axillary scales present with complex covering ~ half of pelvic-fin base. Anal fin with 2 unbranched rays and 5 branched rays (ii,5); first unbranched ray slightly less than 1/3 length of second, closely adhered; fin margin curved with second unbranched ray longest and last branched ray shortest. Caudal fin with 1 unbranched and 8 (4) or 9 (16) branched rays in upper lobe and 8 (16), or 9 (4) branched and 1 unbranched ray in lower lobe (i,8–9,8–9,i); forked with upper and lower lobes coequal. Adipose fin present with base centered on vertical through middle of anal-fin base. Rays of paired, dorsal, and anal fins with thick flaps of skin dorsally (paired fins) and laterally (dorsal and anal fins) that overlap successive rays in adpressed fins; flaps widest and longest anteriorly, decreasing in size and width posteriorly, flaps usually absent on posterior rays.

Teeth tricuspid, narrow and peg-like with median cusp round and lateral cusps poorly developed. 6 (4), 7 (12), or 8 (4) premaxillary teeth. 9 (3), 10 (6), 11 (6), 12 (4), or 14 (1) teeth in outer dentary row. Inner dentary row comprising many small, unicuspid teeth; teeth may be poorly visible or absent in smaller specimens. Ectopterygoid with two rows of approximately 10 (lateral) and 5–10 (medial) minute teeth.

Branchiostegal rays 4; 1 ray attached to posterior ceratohyal; 3 rays attached to anterior ceratohyal. Gill rakers 2–3 on dorsal limb, 1 on angle, 6–7 on ventral limb of anterior branchial arch. One supraorbital present; crescent shaped; from dorsal midpoint of orbit to dorsal ~ 1/4 of anterior scleral ossicle. All elements of infraorbital series, except infraorbital 1, without laminar component. Parietal branch of supraorbital sensory canal extending less than 1/4 into parietal. Parietal fontanel reduced to tiny triangle at posterior borders of parietals, almost absent in some; smallest specimens with gap between parietals. Frontal foramina above supraorbital canal 3–4 with some posterior foramina sometimes combined, wide, circular.

Total number of vertebrae 33 (3). Vertebral centra 2–4 fused, without ventral processes. Rib of centrum 4 distally expanded, extending anteriorly toward lateral process of centrum 2. Posterior chamber of swim bladder extremely reduced, about length of one vertebral centrum. Supraneurals between neural spine of fourth centrum and anterior dorsal-fin pterygiophore 4 (4), 5 (1). Epurals 3 (5). Uroneural present, about 1/2 as long as urostyle.

Coloration in life.— ( Fig. 11 ) Base color tan with slight yellow tinge (particularly on head, fins, and dorsally). Dorsal surface with many (~ 10) diffuse saddles that seem to subdivide in larger specimens. Faint stripe present along lateral line. Numerous narrow bars below lateral line (1–1.5 scale rows wide). These may extend above lateral line and join with dorsal saddles (particularly in larger specimens). Color generally concentrated on scales with each scale having lighter edges, but either anterior or posterior edges may be light. Ventral surface gray with ventral bars almost meeting midventrally. Iridescent yellow-green stripe noticeable in some specimens between midlateral stripe and dorsal surface; stripe located below dark pigment and fades at insertion of posteriormost dorsal-fin ray.

Head with dorsal saddle that extends to near ventral margin of opercle (posterior margin of opercle gray to yellow). Large dark blotches present below and behind eye. Wide stripe present from eye to snout. Dark bands present between orbits and down snout. Amount of melanin on head varies, some individuals with large gray to yellow patches and some almost entirely dark. Iridescent green spot present in some specimens located dorsal to postorbital dark spot.

Dorsal fin with dark distal margin, gray band that changes to yellow proximally, then black band made of spots on rays that covers ~ 1/4 width of fin (interradial membranes gray along band), then narrow gray to yellow band, and finally proximal black band made of roughly triangular spots with longest edges along anterior margins of rays and sloping posteroventrally to posterior margin of rays (interradial membranes gray to yellow); all bands more diffuse anteriorly. Pectoral fin with gray distal margin changing to yellow proximally; dark spots present in two bands distally; distalmost dark band with spots only on rays, but some spots bleed onto membranes in proximal band; dark band at base of pectoral fin may be present; pectoral-fin colors more diffuse ventrally, generally gray with fleshy pads of unbranched and first branched rays almost white. Pelvic fin colored similarly to pectoral with single median band that includes melanophores on interradial membranes and band at base of fin. Anal fin as pelvic fin, but no basal band. Adipose fin yellow to gray proximally and dark distally with dark color confluent with saddle below it. Base color of caudal fin dark with pigment concentrated at junctions of lepidotrichia; two yellow spots present at base (just above and just below midline), single median spot located along midline just after proximal spots, rest of fin with large yellow blotches proximally and large gray blotches distally (gray blotches may fade into base color).

Coloration in alcohol.— ( Fig. 12 ) As in life but yellows and grays become tan and iridescence is lost.

Distribution.— ( Fig. 9 ) Characidium wangyapoik is only known from the upper Ireng River basin (Amazon River) along the Brazil / Guyana border (known as the Rio Mau in Brazil). Specimens were collected from below Orinduik Falls to the upper falls on the Ireng and its equal tributary, the Sukwabi River, but not above the Uluk Tuwuk or Wotawanda falls of the upper Ireng and Sukwabi Rivers (see Lujan et al., 2020, for a more detailed map and description of this area).

Etymology.— Wangyapoik is the Patamona word for the species, and it is used as a noun in apposition. Wang means ‘honey’ and yapoik means ‘seated,’ perhaps in reference to the yellowish color. The Patamona also refer to the species by the English common name of ‘‘fallsfish.’’

Figures

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.

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. 3. Plot of the ratio of orbital diameter to head length versus standard length for all measured specimens of fast-water Characidium of the Guiana Shield showing allometry in eye size.

FIG. 9. Distributions of Characidium declivirostre, C. duplicatum, new species, and C. wangyapoik, new species. Type localities indicated by T’s (approximated for C. declivirostre).