A New Genus and Two New Species of Tetras (Characiformes: Characidae), with a Redescription and Generic Reassignment of Axelrodia lindeae Géry
Since its description, Axelrodia lindeae has always been referred to as morphologically distinct from the remaining species of Axelrodia, with some authors questioning the monophyletic status of the genus. After a comprehensive analysis of representatives of Axelrodia, a new genus represented by A. lindeae as type species, plus two additional new species, is herein proposed. Besides its unique color pattern, characterized by two conspicuous midlateral stripes, the new genus is differentiated from the remaining characid genera by the dentary tooth row, implanted internally, and by the presence of a pseudotympanum crossed by a bundle of epaxialis musculature at its dorsal portion, dividing the pseudotympanum into two muscle hiatuses. Additionally, the phylogenetic relationships between the new genus and Axelrodia among the Characidae are presented.
(A) Amazonichthys lindeae, holotype, MHNG 2229.08, 20.6 mm SL, Rio Amazonas, Igarapé Curuçambá; image provided by the Département d’herpétologie et d’ichtyologie of the Muséum d’Histoire naturelle, Genève. (B) Amazonichthys lindeae, MPEG 26061, male, 20.4 mm SL, Rio Amazonas, Igarapé Rio Branco. (C) Amazonichthys lindeae, MPEG 26063, female, 24.4 mm SL, Rio Tapajós, Igarapé Mutum.
Amazonichthys lindeae, MPEG 31193, male, 19.5 mm SL, Rio Amazonas, Igarapé Curuçambá. (A) Upper and lower jaws, left side, medial view. (B) Skull, lateral view, left side. Abbreviations: aa, angulo-articular; ao, anterorbital; bo, basioccipital; cc, coronomeckelian cartilage; cm, coronomeckelian bone; dt, dentary; ec, ectopterygoid; ep, epioccipital; esc, epiphyseal branch of supraorbital canal; ex, exoccipital; fr, frontal; hm, hyomandibular; io, infraorbital; ioc, infraorbital canal; ip, interopercle; le, lateral ethmoid; mbc, mandibular canal; me, mesethmoid; mp, mesopterygoid; mx, maxilla; ns, nasal; nsc, nasal canal; op, opercle; os, orbitosphenoid; pa, parietal; pl, palatine; pm, premaxilla; po, prootic; pp, preopercle; ppc, preopercle canal; pr, parasphenoid; ps, pterosphenoid; pt, pterotic; ptc, pterotic canal; qd, quadrate; ra, retroarticular; rc, rhinosphenoid cartilage; rs, rhinosphenoid; so, supraoccipital; soc, supraorbital canal; sp, sphenotic; stc, supratemporal canal; su, subopercle; vm, vomer. Black arrows indicate the anterior region.
(A) Caudal skeleton and associated rays of Amazonichthys lindeae in lateral view, left side, MPEG 31193, male, 19.5 mm SL, Rio Amazonas, Igarapé Curuçambá. Abbreviations: dp, dorsal procurrent rays; eu, epural; hs, haemal spine; hy, hypural; lc, lower lobe principal caudal-fin rays; ns, neural spine; uc, upper lobe principal caudal-fin rays; un, uroneural; ur, urostyle; vp, ventral procurrent rays; vt, vertebrae. (B) Humeral region of Amazonichthys lindeae in lateral view, left side, MPEG 31193, female, 24.1 mm SL, Rio Amazonas, Igarapé Curuçambá, with the pseudotympanum in detail. Abbreviations: ct, cleithrum; epx, epaxialis; lsu, lateralis superficialis; oin, obliquus inferioris; op, opercle; osp, obliquus superioris; pe, posttemporal; poc, postotic canal; rb, pleural rib; rla, ramus lateralis accessorius; sc, supracleithrum; su, subopercle. (C, D) Hyobranchial apparatus of Amazonichthys lindeae, MPEG 31193, male, 19.5 mm SL, Rio Amazonas, Igarapé Curuçambá. (C) Branchial arch in dorsal view, right side, except upper elements in ventral view. (D) Hyoid arch and branchiostegals, right side, lateral view. Abbreviations: ac, anterior ceratohyal; bb, basibranchial; bc, basihyal cartilage; bh, basihyal; br, branchiostegal rays; cb, ceratobranchial; dh, dorsal hypohyal; eb, epibranchial; hb, hypobranchial; ih, interhyal; lp, lower pharyngeal; pc, posterior ceratohyal; ss, suspensory pharyngeal; up, upper pharyngeal; vh, ventral hypohyal. (E, F) Pelvic girdle of Amazonichthys lindeae, MPEG 31193, male, 19.5 mm SL, Rio Amazonas, Igarapé Curuçambá, right side. (E) Ventral view. (F) Dorsal view. Abbreviations: is, ischiatic process; pv, pelvic bone; re, radial element. (G) Anal fin of Amazonichthys lindeae, MPEG 31193, male, 19.5 mm SL, Rio Amazonas, Igarapé Curuçambá, left lateral view. Abbreviations: as, anal-fin stay; ba, branched ray; di, distal radial; md, medial radial; px, proximal radial; ub, unbranched ray. Black arrows indicate the anterior region.
Map of northern South America showing the geographic distribution of Amazonichthys lindeae (yellow), A. camelierae (blue), and A. lu (red). Squares indicate type localities. 1, Rio Amazonas; 2, Rio Negro; 3, Rio Tapajós; 4, Rio Madeira.
(A) Amazonichthys camelierae, holotype, MPEG 26653, male, 25.1 mm SL, Rio Amazonas, Rio Tapajós. (B) A. camelierae, MPEG 25273, female, 31.2 mm SL, Rio Amazonas, Rio Tapajós.
Amazonichthys camelierae, LIRP 16999, male, 26.7 mm SL, Rio Amazonas, Rio Tapajós. (A) Upper and lower jaws, left side, medial view. (B) Skull, lateral view, left side. Abbreviations: aa, angulo-articular; ao, anterorbital; bo, basioccipital; cc, coronomeckelian cartilage; cm, coronomeckelian bone; dt, dentary; ec, ectopterygoid; ep, epioccipital; esc, epiphyseal branch of supraorbital canal; ex, exoccipital; fr, frontal; hm, hyomandibular; io, infraorbital; ioc, infraorbital canal; ip, interopercle; le, lateral ethmoid; mbc, mandibular canal; me, mesethmoid; mp, mesopterygoid; mx, maxilla; ns, nasal; nsc, nasal canal; op, opercle; os, orbitosphenoid; pa, parietal; pl, palatine; pm, premaxilla; po, prootic; pp, preopercle; ppc, preopercle canal; pr, parasphenoid; ps, pterosphenoid; psc, parietal branch of supraorbital canal; pt, pterotic; ptc, pterotic canal; qd, quadrate; ra, retroarticular; rc, rhinosphenoid cartilage; rs, rhinosphenoid; so, supraoccipital; soc, supraorbital canal; sp, sphenotic; stc, supratemporal canal; su, subopercle; vm, vomer. Black arrows indicate the anterior region.
(A) Caudal skeleton and associated rays of Amazonichthys camelierae in lateral view, left side, LIRP 16999, male, 26.7 mm SL, Rio Amazonas, Rio Tapajós. Abbreviations: dp, dorsal procurrent rays; eu, epural; hs, haemal spine; hy, hypural; lc, lower lobe principal caudal-fin rays; ns, neural spine; uc, upper lobe principal caudal-fin rays; un, uroneural; ur, urostyle; vp, ventral procurrent rays; vt, vertebrae. (B) Humeral region of Amazonichthys camelierae in lateral view, left side, MPEG 28518, female, 18.3 mm SL, Rio Amazonas, Rio Tapajós, with the pseudotympanum in detail. Abbreviations: ct, cleithrum; epx, epaxialis; lsu, lateralis superficialis; oin, obliquus inferioris; op, opercle; osp, obliquus superioris; pe, posttemporal; ph, postcleithrum; poc, postotic canal; rb, pleural rib; rla, ramus lateralis accessorius; sc, supracleithrum; su, subopercle. (C, D) Hyobranchial apparatus of Amazonichthys camelierae in lateral view, left side, LIRP 16999, male, 26.7 mm SL, Rio Amazonas, Rio Tapajós. (C) Branchial arch in dorsal view, right side, except upper elements in ventral view. (D) Hyoid arch and branchiostegals, right side, lateral view. Abbreviations: ac, anterior ceratohyal; bb, basibranchial; bc, basihyal cartilage; bh, basihyal; br, branchiostegal rays; cb, ceratobranchial; dh, dorsal hypohyal; eb, epibranchial; hb, hypobranchial; ih, interhyal; lp, lower pharyngeal; pc, posterior ceratohyal; ss, suspensory pharyngeal; up, upper pharyngeal; vh, ventral hypohyal. (E, F) Pelvic girdle of Amazonichthys camelierae in lateral view, left side, LIRP 16999, male, 26.7 mm SL, Rio Amazonas, Rio Tapajós, right side. (E) Ventral view. (F) Dorsal view. Abbreviations: is, ischiatic process; pv, pelvic bone; re, radial element. (G) Anal fin of Amazonichthys camelierae in lateral view, left side, LIRP 16999, male, 26.7 mm SL, Rio Amazonas, Rio Tapajós, left lateral view. Abbreviations: as, anal-fin stay; ba, branched ray; di, distal radial; md, medial radial; px, proximal radial; ub, unbranched ray. Black arrows indicate the anterior region.
(A) Amazonichthys lu, holotype, UFRO-I 27663, male, 25.1 mm SL, Rio Amazonas, Rio Madeira. (B) Amazonichthys lu, UFRO-I 15197-I, female, 21.0 mm SL, Rio Amazonas, Rio Madeira.
Amazonichthys lu, MCP 54583, male, 24.3 mm SL, Rio Amazonas, Rio Madeira. (A) Upper and lower jaws, left side, medial view. (B) Skull, lateral view, left side. Abbreviations: aa, angulo-articular; ao, anterorbital; bo, basioccipital; cc, coronomeckelian cartilage; cm, coronomeckelian bone; dt, dentary; ec, ectopterygoid; ep, epioccipital; esc, epiphyseal branch of supraorbital canal; ex, exoccipital; fr, frontal; hm, hyomandibular; io, infraorbital; ioc, infraorbital canal; ip, interopercle; le, lateral ethmoid; mbc, mandibular canal; me, mesethmoid; mp, mesopterygoid; mx, maxilla; ns, nasal; nsc, nasal canal; op, opercle; os, orbitosphenoid; pa, parietal; pl, palatine; pm, premaxilla; po, prootic; pp, preopercle; ppc, preopercle canal; pr, parasphenoid; ps, pterosphenoid; psc, parietal branch of supraorbital canal; pt, pterotic; ptc, pterotic canal; qd, quadrate; ra, retroarticular; rc, rhinosphenoid cartilage; rs, rhinosphenoid; so, supraoccipital; soc, supraorbital canal; sp, sphenotic; stc, supratemporal canal; su, subopercle; vm, vomer. Black arrows indicate the anterior region.
(A) Caudal skeleton and associated rays of Amazonichthys lu in lateral view, left side, MCP 54583, male, 24.3 mm SL, Rio Amazonas, Rio Madeira. Abbreviations: dp, dorsal procurrent rays; eu, epural; hs, haemal spine; hy, hypural; lc, lower lobe principal caudal-fin rays; ns, neural spine; uc, upper lobe principal caudal-fin rays; un, uroneural; ur, urostyle; vp, ventral procurrent rays; vt, vertebrae. (B) Humeral region of Amazonichthys lu in lateral view, left side, INPA 26832, 16.4 mm SL, Rio Negro, Rio Branco, with the pseudotympanum in detail. Abbreviations: ct, cleithrum; epx, epaxialis; lsu, lateralis superficialis; oin, obliquus inferioris; op, opercle; osp, obliquus superioris; pe, posttemporal; poc, postotic canal; rb, pleural rib; rla, ramus lateralis accessorius; sc, supracleithrum; su, subopercle. (C, D) Hyobranchial apparatus of Amazonichthys lu in lateral view, left side, MCP 54583, male, 24.3 mm SL, Rio Amazonas, Rio Madeira. (C) Branchial arch in dorsal view, right side, except upper elements in ventral view. (D) Hyoid arch and branchiostegals, right side, lateral view. Abbreviations: ac, anterior ceratohyal; bb, basibranchial; bc, basihyal cartilage; bh, basihyal; br, branchiostegal rays; cb, ceratobranchial; dh, dorsal hypohyal; eb, epibranchial; hb, hypobranchial; ih, interhyal; lp, lower pharyngeal; pc, posterior ceratohyal; ss, suspensory pharyngeal; up, upper pharyngeal; vh, ventral hypohyal. (E, F) Pelvic girdle of Amazonichthys lu in lateral view, left side, MCP 54583, male, 24.3 mm SL, Rio Amazonas, Rio Madeira, right side. (E) Ventral view. (F) Dorsal view. Abbreviations: is, ischiatic process; pv, pelvic bone; re, radial element. (G) Anal fin of Amazonichthys lu in lateral view, left side, MCP 54583, male, 24.3 mm SL, Rio Amazonas, Rio Madeira, left lateral view. Abbreviations: as, anal-fin stay; ba, branched ray; di, distal radial; md, medial radial; px, proximal radial; ub, unbranched ray. Black arrows indicate the anterior region.
Phylogenetic relationships between Amazonichthys and Axelrodia among the Characidae with the inclusion of morphological data of the three species of Amazonichthys (A. lindeae, MPEG 31193; A. camelierae, LIRP 16999; and A. lu, MCP 54583) and of Axelrodia stigmatias (INPA 29258), and the inclusion of morphological and molecular data (COX1) of Aphyocharacidium melandetum (ANSP 177067 and MHNG 2759.090, respectively) to the matrix data of Mirande (2019), maintaining the molecular data of Aphyocharacinae sp. (A. bolivianum, LBP 9055 of Mirande, 2019) and the morphological data of A. bolivianum (MCP 37960). Phylogeny obtained from the combined phylogenetic analysis under parsimony and extended implied weighting (BLK; k = 42.85903; fit = 957.80766; length = 79.628 steps). Support is expressed as GC-values (differences of frequencies “group present/contradicted”). See Supplemental Appendix 1 for details. See Data Accessibility for tree file.
Contributor Notes
Associate Editor: R. E. Reis.