Gymnocorymbus thayeri Eigenmann, 1908

Benine, Ricardo C., Melo, Bruno F., Castro, Ricardo M. C. & Oliveira, Claudio, 2015, Taxonomic revision and molecular phylogeny of Gymnocorymbus Eigenmann, 1908 (Teleostei, Characiformes, Characidae), Zootaxa 3956 (1), pp. 1-28 : 17-20

Gymnocorymbus thayeri Eigenmann, 1908

Fig. 12 , Table 5

Gymnocorymbus thayeri Eigenmann, 1908: 93 . Type locality: “Amazons from Tabatinga to Gurupa” ( Brazil).

Diagnosis. Gymnocorymbus thayeri is distinguished from G. bondi by the number of gill rakers on lower limb of the first branchial arch (14–16 vs. 11–12, respectively). It differs from G. ternetzi and G. flaviolimai by the number of scale rows covering the base of the anal fin (2–4 vs. 5–6, respectively); by the shape of the distal margin of the anal fin (straight, or slightly convex vs. strongly convex, respectively); by the number of pelvic-fin rays (i,7 vs. i,6, respectively). Further differs from G. ternetzi by the number of cusps of the teeth in the inner tooth row of the premaxillar (5–7 vs. 3, respectively); by the overall color pattern (lack of a dense field of dark chromatophores scattered homogeneously over the posterior one half of the body vs. the presence of such pigmentation, respectively) and by the shape of the first humeral blotch (the presence of a wider densely pigmented region above the lateral line vs. the absence of such pigmented region, respectively; Fig. 6 ).

Description. Morphometric data for Gymnocorymbus thayeri is summarized in Table 5 . Body deep. Largest specimen examined 80.9 mm SL. Greatest depth at origin of dorsal fin. Dorsal profile of head slightly concave. Dorsal profile of body convex from posterior tip of supraoccipital to end of dorsal-fin base; slightly convex from rear of dorsal-fin base to end of adipose-fin base. Caudal peduncle profile slightly concave both dorsally and ventrally. Ventral profile of head and body convex from tip of lower jaw to caudal peduncle origin. Prepelvic region slightly keeled medially; flattened proximate to pelvic-fin insertion. Postpelvic median keel extending from pelvic-fin insertion to anal-fin origin.

Supraoccipital process elongate; tip extends beyond vertical through posterior margin of opercle.

Mouth terminal. Maxillar extending beyond vertical through anterior margin of orbit nearly to the vertical through middle of orbit. Premaxillary teeth in two rows. Outer row with 4* (47), 5 (18), or 6 (1) tricuspidate teeth with central cusp longest. Inner tooth row with 4 (8), 5* (54), or 6 (2) teeth with four cups (in the asymmetrical symphyseal tooth) or five to seven cusps, central cusp longest. Maxillar lacking teeth (9), with 1* (56), or 2 (12) tricuspidate teeth. Dentary with five pentacuspidate teeth, usually central cusp longest, followed by one to three small conical or tricuspidate teeth.

Dorsal-fin rays ii, 9*. Pectoral-fin rays i,9,i (6), i,10,i (58), or i,11,i* (71). Tip of pectoral fin extends beyond midlength of adpressed pelvic fin. Adipose fin present. Pelvic-fin rays i,7. Tip of adpressed pelvic fin reaches first branched ray of anal fin. Anal-fin rays iv,32 (6), 34 (8), 35* (55), 36 (32), 37 (26), 38 (22), 39 (8), or 40 (1). Principal caudal-fin rays i,17,i. Caudal fin forked.

Scales cycloid. Lateral line complete with 31 (6), 32 (23), 33* (56), 34 (25) or 35 (4) scales. Scale rows between lateral line and dorsal-fin origin 7 (7), 8* (94), or 9 (7). Scale rows between lateral line and pelvic-fin origin 8* (89) or 9 (52). Circumpeduncular scale rows 12* (21), 13 (25), or 14 (28). Scale sheath along anal-fin base with two to four series along length of anal-fin base.

First gill arch, with 8 (38), 9 (38), 10 (3) or 11 (19) gill rakers on upper limb and 13 (48), 14 (28), 15 (18) or 16 (4) gill rakers on lower limb. Total vertebrae 33, supraneurals 4.

Color in alcohol. Overall coloration yellow tan, with homogeneous field of dark chromatophores scattered over posterior half of body. Dark chromatophores more densely concentrated along dorsal midline. Dense field of dark chromatophores on both lips, and dorsal third of maxilla. Infraorbital and opercular series with silvery pigmentation due to the presence of guanine. Vertical dark stripe as wide as pupil crossing orbit. Two conspicuous vertical dark humeral marks. Anterior humeral mark narrower than posterior humeral mark. Anterior humeral mark, located over second to fourth lateral line scales and extending over five horizontal scale rows above lateral line and four to five horizontal scale rows below lateral line. Posterior humeral mark located over ninth to twelfth lateral line scales and extending over six horizontal scale rows above lateral line and four to five horizontal scale rows below lateral line. Dorsal and anal fins homogenously dark pigmented. Paired fins and caudal fin with few dark dispersed chromatophores, more so on unbranched rays. Adipose fin densely dark pigmented, more so along its dorsal border.

Distribution. Gymnocorymbus thayeri occurs in Corantijn and Amazon basins along with the Rio Gurupi and Rio Parnaíba of northeastern Brazil. Records of G. thayeri in Guyana and Trinidad and Tobago ( Lima et al. 2003) could not be confirmed. Records from the Río Apure in the Orinoco basin ( Taphorn 2003) could not be evaluated since we were not able to examine the vouchers but very likely refer to G. bondi .

Remarks. According to the original description, Gymnocorymbus thayeri Eigenmann, 1908 was described based on one hundred specimens. The examination of the syntypes at the Museum of Comparative Zoology (MCZ) revealed the presence of exactly 108 specimens. We herein designate MCZ 89967 as the lectotype and the remaining 107 syntypes (MCZ 19242, MCZ 19272, MCZ 20710, MCZ 20720, MCZ 20724, MCZ 20789, MCZ 20804, MCZ 20807, MCZ 20973, MCZ 20984, MCZ 20998, MCZ 21001, MCZ 21007, MCZ 21065) accordingly become paralectotypes. The examination of the holotype of Moenkhausia latissima confirmed Lima et al. (2003) in not recognizing it as a species of Gymnocorymbus .

Material examined. Types: MCZ 89967, lectotype, 39.9 mm SL, Brazil, Amazonas, Tefé, Rio Solimões, Oct 1865, L. Agassiz (by present designation). Paralectotypes, 107 specimens, 19 measured. All from Brazil. Pará: MCZ 20724, 1, 50.7 mm SL, Gurupá, Rio Amazonas delta at Gurupá, 1°25’S 51°36’W. MCZ 20789, 22, not measured, Santarém, 2°26’S 54°41’W. Amazonas: MCZ 19242, 1, 29.5 mm SL. Brazil, Amazonas: Rio Solimões at Tabatinga. MCZ 19272, 1, not measured; MCZ 20973, 4, not measured, Rio Solimões, Lago Codajás, 3°24’S 62°38’W. MCZ 20710, 2, not measured; MCZ 20720, 2, not measured, Villa Bella, Rio Amazonas at Parintins, 2°38’S 56°45’W. MCZ 20804, 1, 53.8 mm SL; MCZ 20807, 9, not measured, Manacupuru, Lago Manacapuru, 3°06’S 61°30’W. MCZ 20984, 29, not measured, Itacoatiara, Serpa, 3°06’S 58°22’W. MCZ 21001, 7, 34.7–40.7 mm SL, Lago José Fernandes (locality unknown, presumably near Manaus). MCZ 21007, 8, 43.5 mm SL (one specimen measured), same data as MCZ 21001. MCZ 20998, 10, not measured, Silves, Lago Saraca, 2°53’S 58°21’W. MCZ 21065, 10, 36.4 mm SL (one specimen measured), same data as MCZ 20998. Non-types: 167 specimens (18.9–80.9 mm SL). Suriname, Nickerie District: USNM 225780, 1, not measured, tributary to Sisa Creek, north side approximately 700 m downstream of crossing of Amotopo to Camp Geologie Road, 3°42’0.0”S 57°37’12.0”W. USNM 225781, 30.0 mm SL, stream on south bank of Lucie River ca 6 km upstream of ferry crossing on Amotopo to Camp Geologie Road, 3°36’0.0”S 57° 42’0.0”W. Ecuador: ANSP 130538, 5, 26.6–42.4 mm SL, Río Aguarico at Santa Cecilia, Napo. ANSP 130539, 8, 20.3–46.2 mm SL, 1 c&s, 44.1 mm SL, Lower Lake at Santa Cecília, Napo. FMNH 103161, 1, 29.5 mm SL; FMNH 103164, 3, 25.0–27.0 mm SL; FMNH 103167, 3, 18.9–59.7 mm SL, Río Sansahuari, at bridge (km 32.5) on road to Río San Miguel, and overflows channels (Río Cuyabeno–Río Aguarico drainage), Napo. Brazil: Pará: INPA 3270, 6, 41.0– 45.4 mm SL, Rio Trombetas, Igarapé Caxipacoré. INPA 12231, 29, 39.4–45.7 mm SL, Rio Trombetas, Igarapé Caxipacoré. MCP 25623, 7, 39.4–43.8 mm SL, Santa Luzia do Pará, Rio Gurupi, Pará–Maranhão road, 1°48’01”S 46°19’00”W. Amazonas: LBP 18027, 1, 43.8 mm SL, Igarapé do Alencar, Rio Amazonas, Itacoatiara, 3°05’57.7”S 58°27’18.0”W. MCZ 92880, 1, 38.5 mm SL; MCZ 92881, 2, 40.2–44.2 mm SL; MCZ 92882, 1, 61.3 mm SL, Lago Jacaretinga, off Rio Amazonas near Manaus. MZUSP 6280, 17, 27.0– 40.8 mm SL, Tabatinga, Rio Solimões, Rio Purus, Lago Castro. MZUSP 9632, 3, 25.7–41.5 mm SL, Codajás, Lago Supiá, in front of Codajás. MZUSP 17411, 2, 47.2–30.0 mm SL, Igarapé in Jacaré, near to Fonte Boa. MZUSP 92289, 17, 2 c&s, 29.7–45.1 mm SL, Rio Tiquié (Rio Negro basin), between São José “do meio” and Floresta viilages, 0º13’00”N 69º36’00”W. MZUSP 93375, 5, 54.3–80.9 mm SL, Rio Tiquié, Pirarara-Poço village, 0°08’40”S 69°12’41”W. Acre: LBP 4176, 1, 22.9 mm SL, Igarapé Preto, rio Juruá, Cruzeiro do Sul, 7°35’33.4”S 72°45’17.7”W. LBP 7722, 1, 25.3 mm SL, Igarapé São Francisco, Rio Acre, Rio Purus, municipality of Rio Branco, 9°56.271’S 67°52.923’W. LBP 10548, 2, 36–39.8 mm SL, Igarapé São Francisco, Rio Acre, Rio Purus, municipality of Rio Branco, 9°55’52.9”S 67°53’07.8”W. LBP 17529, 4, 26.0–31.0 mm SL; LBP 17530, 1, 35.8 mm SL, Açude Recanto do Socó, Rio Acre, Rio Purus, municipality of Rio Branco, 9°56’31.0”S 67°53’46.2”W. MZUSP 29932, 17, 33.6–51.0 mm SL, Tarauacá, Rio Tarauacá, Igarapé da Entendência. Maranhão: MCP 25622, 2, 39.7–44.1 mm SL, Maracaçumé, Rio Supriano, 2°00’28”S 45°58’22”W. MCP 25628, 2, 40.0– 43.1 mm SL, Timon, Rio Parnaíba, Igarapé do Pinto, Pará– Maranhão road (BR 316) about 58 km SE Caxias, 5°03’3”S 42°53’3”W. Peru: LBP 17742, 6, 30.5–41.5 mm SL, Coronel Portillo, Pucallpa, Río Ucayali, 8°34’14,”S 74°48’05,7”W. LBP 17756, 13, 32.0– 42.3 mm SL, Coronel Portillo, Pucallpa, Río Ucayali, 8°32’47,8”S 74°48’14,7”W. LBP 17803, 1, 25.9 mm SL, Quebrada Agua Blanca, Río Ucayali, Coronel Portillo, Pucallpa, 8°35’44.2”S 74°48’04.3”W. LBP 19551, 1, 52.0 mm SL; ZUEC 8676, 4, 39.8–61.0 mm SL, Loreto, Iquitos, Iquitos/Nauta road, ca. 31 km S from Iquitos, 3°59'50.0''S, 73°25'42.0''W.

Figures

FIGURE 6. Graphical representation of the differences in the pattern of the humeral mark pigmentation in (a) Gymnocorymbus ternetzi and (b) G. bondi and G. thayeri.

FIGURE 12. Gymnocorymbus thayeri. a) Lectotype of Gymnocorymbus thayeri, MCZ 89967, 39.9 mm SL, Tefé, Rio Solimões, Rio Amazonas basin, Brazil; b) Specimen of G. thayeri, LBP 9163, 56.4 mm SL, Rio Amazonas, near Iquitos, Peru; c) Specimen of G. thayeri, ANSP 130539, 46.2 mm SL, Río Napo, Rio Amazonas basin, Ecuador; d) Specimen of G. thayeri, MZUSP 93375, 80.9 mm SL, Río Tiquié, upper Rio Negro, Brazil. Photo (a) by Museum of Comparative Zoology, Harvard University.

Tables

TABLE 5. Morphometric data for Gymnocorymbus thayeri; N includes lectotype.

	N	Lectotype	Range	Mean
Standard length (mm)	181	39.9	18.9–80.9	–
Percentage of standard length
Greatest depth	181	56.0	47.5–65.6	54.3
Snout to dorsal-fin origin	181	53.7	50.9–58.0	54.1
Snout to pectoral-fin origin	164	32.9	28.8–35.3	32.0
Snout to pelvic-fin origin	181	50.9	43.2–58.7	48.5
Snout to anal-fin origin	164	63.8	56.5–69.1	61.3
Caudal peduncle depth	181	9.0	8.4–12.8	10.2
Caudal peduncle length	164	7.6	6.8–11.2	8.5
Pectoral-fin length	181	22.8	16.7–28.5	25.6
Pelvic-fin length	181	16.5	14.6–21.3	18.0
Dorsal- fin length	173	31.1	27.8–40.7	34.6
Dorsal-fin base	181	19.8	14.4–20.1	17.0
Anal-fin length	178	19.8	17.8–28.4	23.0
Anal-fin base	178	47.5	41.7–52.1	47.0
Eye to dorsal fin origin	164	43.6	38.5–46.5	41.7
Dorsal fin origin to caudal fin origin	164	59.1	52.4–70.0	56.6
Head length	181	28.9	26.1–34.2	30.0
Head depth	178	25.2	20.2–34.8	24.2
Percentage of head length
Snout length	181	27.2	20.3–31.7	23.9
Upper jaw length	164	44.0	39.5–47.3	43.0
Horizontal orbital diameter	181	38.0	35.5–49.8	41.7
Least interorbital width	181	34.2	27.5–42.7	33.8