A new species (Microcharacidium bombioides sp. nov.) of the genus Microcharacidium Buckup, 1993 is described from the Rio Negro, Rio Trombetas, Rio Tapajós, tributaries of the Rio Madeira, and the middle Rio Amazonas. The new species is promptly distinguished from all congeners (Microcharacidium eleotrioides (Géry, 1960), Microcharacidium gnomus Buckup, 1993, and Microcharacidium weitzmani Buckup, 1993) by the presence of 12 circumpeduncular scales, 19 precaudal vertebrae, and 7 dark bars on the flanks connected to their contralateral parts both dorsally and ventrally; 2 short, dark suborbital stripes; all teeth on both jaws conical; 10–11 total dorsal-fin rays; and 3–4 perforated lateral line scales. An updated identification key for the genus is provided and the affinities of the new species with other Microcharacidium are discussed.
Une nouvelle espèce de poisson (Microcharacidium bombioides sp. nov.) du genre Microcharacidium Buckup, 1993 est décrite des rivières Negro, Trombetas et Tapajós, d’affluents de la rivière Madeira et du cours intermédiaire du fleuve Amazone. La nouvelle espèce se distingue rapidement de tous ses congénères (Microcharacidium eleotrioides (Géry, 1960), Microcharacidium gnomus Buckup, 1993 et Microcharacidium weitzmani Buckup, 1993) par la présence de 12 écailles circumpédonculaires, 19 vertèbres précaudales et 7 bandes foncées sur les flancs reliées dorsalement et ventralement, 2 courtes bandes suborbitales foncées, la forme conique de toutes les dents des deux mâchoires, de 10 à 11 rayons au total sur la nageoire dorsale et de 3 à 4 écailles perforées le long des lignes latérales. Une clé d’identification actualisée est présentée pour le genre et les affinités de la nouvelle espèce avec d’autres Microcharacidium sont abordées. [Traduit par la Rédaction]
The genus Microcharacidium Buckup, 1993 currently includes three valid species of characidiins: Microcharacidium eleotrioides (Géry, 1960), Microcharacidium gnomus Buckup, 1993, and Microcharacidium weitzmani Buckup, 1993; all three are considered miniatures (sensu Weitzman and Vari 1988) with the maximum size of less than 26 mm standard length (Toledo-Piza et al. 2014). The genus is widely distributed throughout cis-Andean northern South America, with representatives occurring in the upper Orinoco, most of the Rio Amazonas basin, and adjacent coastal basins draining from the Guiana and Brazilian shields (Buckup 1993a, 2003; Ohara et al. 2013; Buckup and Van der Sleen 2017). The diagnostic features originally proposed for the genus recognition are (1) the presence of 17 principal caudal-fin rays; (2) constriction of the space between the pelvic bones; (3) fusion of postcleithra 1 and 2; and (4) the presence of a longitudinal stripe, which is broad and with well-defined edges, when compared representatives of other characidiin genera, and especially Characidium Reinhardt, 1867 (Buckup 1993b).
Zarske (1997) described a fourth species for the genus, “Microcharacidium” geryi, which was assigned to Microcharacidium based mainly on the absence of maxillary teeth and the reduced number of rays on the caudal and pectoral fins (17 caudal-fin rays and 8–9 pectoral-fin rays). However, the inclusion of that species in the genus was questioned by Buckup (2003), who considered M. geryi incertae sedis in Crenuchidae. Later, Melo et al. (2016) suggested relocating the species to Characidium, classification assumed since then.
The number of circumpeduncular scales is an important diagnostic character allowing for the prompt recognition of M. gnomus (14 scales) from M. eleotrioides and M. weitzmani (both with 10 scales), with the distinction between the latter two based mostly on the number of tooth cusps, and the number of scales of the lateral line series, among other characters (Buckup 1993b). During a revisionary study of the genus, an additional species with a color pattern resembling that of M. eleotrioides with 12 circumpeduncular scales and conical teeth was identified from the middle Rio Amazonas and its major tributaries in the central Amazon, and it is described herein. In addition, an updated identification key for the genus is provided and the affinities of the new species with other Microcharacidium are discussed.
Materials and methods
Counts and measurements followed Buckup (1993b). Measurements were made under a stereoscopic microscope (Binocular Model; zoom 0.8× ∼ 5×, magnification 8× ∼ 50×, and 2 W transmitted and reflected LED illumination) with a scaled reticle. All measurements are presented as proportions of standard length (SL), except for subunits of the head, which are presented as proportions of the head length (HL). In the description, the values for each meristic data are followed by their frequency in parentheses with an asterisk indicating the values for the holotype. Counts of vertebrae, supraneurals, procurrent caudal-fin rays, branchiostegal rays, and teeth were taken from cleared and stained paratypes (C and S), prepared according to Taylor and Van Dyke (1985). The total number of vertebrae includes those of the Weberian Apparatus (counted as four elements) and the fused preural 1 (PU1+) with ural 1 (U1) of the caudal region as a single element. In the present contribution, bars are preferred over vertical bands (sensu Buckup 1993b) as a more widely employed term for vertically arranged color pattern elements in the Characiformes literature.
Institutional abbreviations are Academy of Natural Sciences of the Drexel University (ANSP), Instituto Nacional de Pesquisas da Amazônia (INPA), Museo de Biología de la Universidad Central de Venezuela (MBUCV), Natural History Museum of Geneva (MHNG), Museu Nacional do Rio de Janeiro (MNRJ), Museu Paraense Emílio Goeldi (MPEG), Museu de Zoologia da Universidade de São Paulo (MZUSP), Universidade Federal do Rio Grande do Sul (UFRGS), and National Museum of Natural History/Smithsonian Institution (USNM).
Microcharacidium eleotrioides non-Géry, 1970 — Dias et al. 2010 (environmental impact study, inferred according to the distribution); Rodrigues-Filho et al. 2018 (ecological study, inferred according to the distribution).
UFRGS 28560, 15.7 mm SL, Brazil, Amazonas, Novo Airão, Rio Negro basin (02°37′17″S, 60°56′39″W), 07 Sep 2007, H.M.V. Espírito Santo.
All from Brazil, Rio Amazonas basin: ANSP 207545 (3, 11.4–15.0 mm SL), INPA 29389 (34, 11.0–15.5 mm SL), MNRJ 52125 (4, 12.7–16.1 mm SL), MZUSP 125821 (4, 10.6–15.4 mm SL), UFRGS 28565 (7, 12.0–16.2 mm SL) collected with the holotype; INPA 29912 (29, 10.0–13.5 mm SL), Amazonas, Manaus (03°06′07″S, 60°1′30″W), 11 Jul 2005, L.N. Carvalho; INPA 31722 (33, 10.0–15.5 mm SL), Amazonas, Itacoatiara (03°08′35″S, 58°26′39″W), 26 Jul 2007, M.S. Dias; INPA 32754 (7, 12.7–14.7 mm SL), Amazonas, Novo Airão (02°37′17″S, 60°56′39″W), 05 Apr 2008, M.S. Dias, R.G. Frederico; INPA 37394 (9, 13.5–15.1 mm SL), Amazonas, São Sebastião do Uatumã (02°34′17″S, 57°52′13″W), 23 Sep 2011, L. Rapp Py-Daniel et al.; MPEG 14585 (14.0 mm SL), Pará, Oriximiná, Rio Patauá (01°45′31″S, 56°21′40″W), 11 Jun 2007, L.F.A. Montag; MPEG 24056 (14, 10.0–12.8 mm SL), Pará, Santarém, Rio Maró, afluente do rio Arapiuns (03°10′32″S, 56°20′38″W), 17 Jun 2011, N. Benone; MPEG 24080 (13, 10.5–13.5 mm SL; 2 C and S), Pará, Santarém, Rio Maró, afluente do rio Arapiuns (03°10′56″S, 55°50′57″W), 17 Jun 2011, N. Benone; MPEG 26000 (4, 12.1–13.1 mm SL), Pará, Juruti, Igarapé da Ponte (02°10′48″S, 56°04′40″W), 29 Nov 2012, M. Mendonça; MPEG 30301 (5, 13.0–16.4 mm SL), Pará, Juruti, Igarapé Rio Branco (02°20′58″S, 56°01′26″W), 12 Dec 2013, M. Mendonça; MPEG 30303 (6, 10.6–12.6 mm SL), Pará, Juruti, Igarapé Café Torrado (02°18′02″S, 56°04′21″W), 12 Dec 2013, M. Mendonça; MPEG 32637 (11, 13.6–15.0 mm SL), Pará, Juruti, Igarapé Socó (02°27′31″S, 56°00′54″W), 22 Mar 2015, M. Mendonça; MPEG 32638 (7, 11.3–12.7 mm SL), Pará, Juruti, Igarapé São Francisco (02°34′52″S, 55°54′11″W), 26 Mar 2015, M. Mendonça; MPEG 32639 (32, 13.1–14.0 mm SL), Pará, Juruti, Igarapé Mutum (02°36′46″S, 56°11′37″W), 20 Mar 2015, M. Mendonça; UFRGS 28565 (7, 12.0–16.2 mm SL), Amazonas, Novo Airão (02°37′17″S, 60°56′39″W), 07 Sep 2007, H.M.V. Espírito Santo.
Microcharacidium bombioides sp. nov. differs from all congeners by the presence of 12 circumpeduncular scales (compared with 10 in M. eleotrioides and M. weitzmani and 14 in M. gnomus), the presence of 19 precaudal vertebrae (compared with 16–17), and the presence of 7 dark bars on the body connected to their contralateral parts both dorsally and ventrally (compared with 8–9 not contacting their contralateral parts ventrally). The new species further differs from M. weitzmani and M. gnomus by the presence of two, short dark suborbital stripes (compared with a single suborbital stripe). Microcharacidium bombioides differs from M. eleotrioides by the having conical teeth on both jaws (compared with tricuspid teeth), and from M. gnomus by the presence of less total dorsal-fin rays (10–11 compared with 12) and the presence of less perforated scales in the lateral line series (3–5 compared with 7–11).
Morphometric data for the holotype and 66 paratypes are summarized in Table 1. Body fusiform, relatively compressed. Head comparatively short (4.0% of SL). Greatest body depth anterior to dorsal-fin origin, between pectoral and pelvic fins. Dorsal profile slightly convex between snout and vertical through half of orbit, inclined to supraoccipital region; uniformly convex from that point to dorsal-fin terminus, almost straight to that point to anteriormost dorsal caudal-fin procurrent ray. Ventral profile slightly convex from snout tip to vertical through pectoral-fin insertion, becoming distinctly convex from that point to anal-fin origin and slightly concave from that point to anteriormost ventral caudal-fin procurrent ray.
Snout smoothly rounded in dorsal view. Mouth small and subterminal. Premaxillary with single row of 12(1) or 13(1) conical teeth decreasing in size laterally. Maxillary edentulous; posterior margin reaching vertical line over anterior margin of orbit. Dentary with two series of teeth. Outer series with 11(1) or 12(1) conical teeth; inner series with 14(1) or 15(1) conical teeth; relatively smaller than those of outer series. Ectopterygoid with small, conical teeth. Endopterygoid edentulous. Branchiostegal rays 4(2); three (2) attached to anterior ceratohyal, one (2) attached to posterior ceratohyal. Supraorbital absent. Parietal branch of the supraorbital sensory canal absent. Supraorbital laterosensory canal not connected to pterotic canal. Large parietal fontanel bordered anteriorly by frontal bones, laterally by parietals and posteriorly by supraoccipital. Frontal foramina above the supraorbital canal absent.
Anterior and posterior nostrils distinctly separated by fleshy bridge, anterior nostril diameter smaller than posterior nostril diameter, approximately circular, dermal flap present. Posterior nostril with small dermal flap on margin; closer to orbit than to anterior nostril. Orbit circular, margins free, approximately on median portion of head. Cheek narrower than orbit, depth about half to two-thirds orbital diameter.
Scales cycloid. Lateral line longitudinal series with 19(1), 20(1), 21(3), 22(10), 23(12), 24(13), 25(10), 26*(11), or 27(1) scales, of which 3(16), 4*(44), or 5(5) are perforated. Series of scales above lateral line 2(1), 3*(62), or 4(2); series below lateral line 2(2), 3*(56), or 4(6). Axillary scale present. Predorsal scales 7(8), 8(25), 9*(24), 10(6), or 11(3). Isthmus completely scaled. Circumpeduncular scales 12*(67). Pseudotympanum formed by well-developed muscular hiatus, relatively large and rounded, exposing the rib of the fifth vertebra (see details in the Remarks below).
Pectoral-fin rays iv,1(1), iv,2(6), iii,3(3), iv,3*(35), ii,4(2), iii,4(8), iv,4(1), or ii,5(1); second, third and fourth rays longest, reaching pelvic-fin origin. Pelvic-fin rays ii,4(27), i,5*(33), or ii,5(5); first ray at vertical through dorsal-fin origin; third longest, not reaching anal-fin origin. Supraneurals 4(2), anterior to neural spines of vertebral centra 6–9(2). First dorsal-fin pterygiophore inserted anteriorly to neural spine of centrum 10(2). Dorsal-fin origin slightly ahead of pelvic-fin insertion, distinctly closer to snout tip than to caudal-fin base; dorsal-fin rays iv,4(1), iv,5(3), v,5(1), iii,6(13), iv,6*(11), v,6(1), ii,7(3), iii,7(8), iv,7(15), ii,8(1), or iii,8(8); second and third rays longest, usually reaching adipose-fin origin, last ray adnate. Adipose fin present. Anal-fin rays i,4(1), ii,4*(59), i,5(4), or ii,5(1); origin posterior to dorsal-fin terminus; third, fourth and fifth ray longest. First anal-fin pterygiophore inserted anteriorly to haemal spine of 22(2) centrum. Principal caudal-fin rays 14(1), 15(7), 16*(56), or 17(1); procurrent caudal-fin rays, dorsal 2(1) or 5(1), ventral 2(1) or 5(1). Epurals 2(2). Uroneurals absent. Precaudal vertebrae 19(2), caudal 12(1) or 13(1); total vertebrae 31(1) or 32(1). Posterior chamber of swimbladder elongate, approximately three times larger than anterior chamber; posterior margin of posterior chamber reaching rib of vertebra 16 or 17.
color in alcohol:
Background color of body light yellow. Back of head with brown chromatophores scattered between the upper lip and the anterior region of frontal bones. Head with dark brown longitudinal stripe, originating at snout tip, across eye and ending near anterodorsal portion of opercle. Two small dark suborbital bars, in an inverted V-shape from ventral margin of eye towards articulation of angulo-articular with quadrate; two dark bars on head, below longitudinal stripe towards ventral portion of head — between preopercle and opercle; and through posterior margin of opercle, ahead pectoral-fin origin; large, dark chromatophores scattered onto opercle. Well-defined dark supraorbital spot, between the dorsal margin of the orbit and the sides of the frontal bones. Predorsal area with brown round blotch. Skin folds of anterior nostrils intensely pigmented; skin folds of posterior nostrils with scarce pigmentation. Body scales with chromatophores close to distal margins. Humeral blotch present, usually diffuse. Longitudinal stripe present, posterior to humeral blotch, passing throughout flanks, becoming broader near caudal peduncle, and extending to caudal-fin rays base. Dark bars on body 7*(67) — first bar immediately past pectoral-fin base, second ahead of the dorsal-fin origin, third near vertical through middle of dorsal-fin base, fourth posterior to dorsal-fin terminus, fifth ahead of anal-fin, the sixth at anal-fin base, and seventh on caudal-peduncle tip; all bars (except the first in some specimens) extending from dorsal portion and reaching ventral region of body, usually two or three scales wide; space between bars usually equivalent to the width of one or two scales. Base of first dorsal-fin ray with an irregular dark pigmentation; each dorsal-fin ray with three to six small brown blotches, forming two to three stripes. Pectoral and pelvic fins usually hyaline, some specimens with two or three irregular brown blotches onto rays. Anal fin with two brown blotches near its base, and three dark blotches on the median portion of rays, forming a small transverse band. Two small, semicircular brown blotches at base of caudal-fin rays. Adipose fin brown near its base and hyaline on distal half.
No secondary sexually dimorphic character was observed among specimens of M. bombioides, although ripe female specimens may present a discretely deeper body.
The new species is widely distributed in the middle Rio Amazonas and its tributaries Rio Negro, Rio Trombetas, and Rio Tapajós (Fig. 2).
The specific epithet bombioides is given in allusion to the colour pattern of the new species consisting of thick, dark bars, alternated by clear, light areas, resembling that of the common bumblebees of the genus Bombus Latreille, 1802 (Hymenoptera, Apidae) plus the suffix -oides (= similar to). A noun.
The inclusion of M. bombioides in the genus Microcharacidium is justified herein because the new species presents all four synapomorphies proposed by Buckup (1993b) for Microcharacidium: (1) the presence of 17 or less principal caudal-fin rays; (2) the constriction of the space between the pelvic bones; (3) the fusion of postcleithra 1 and 2; and (4) the presence of a longitudinal stripe, which is broad and with well-defined edges, when compared with that of representatives of other characidiin genera, especially Characidium.
Besides the differences in the number of circumpeduncular scales, predorsal vertebrae, and bars detailed in the diagnosis section allowing for the recognition of M. bombioides, it shares several morphological characters with M. eleotrioides and M. weitzmani. Most of the meristic data for the three species overlap and the characters referring to the color present subtle differences in each species of the genus. Buckup (1993c) recognizes in his phylogenetic study a close relationship between M. eleotrioides and M. weitzmani, that group sister to M. gnomus. Thus, the sharing of numerous morphological features among M. bombioides, M. eleotrioides, and M. weitzmani could be indicative that the new species would be more closely related to the first two than to M. gnomus. However, these assumptions will remain open until a detailed phylogeny addressing all species of Microcharacidium is provided.
Microcharacidium eleotrioides — Holotype image, MHNG 2201.13 (20.5 mm SL); MZUSP 108858 (16.7 mm SL); MZUSP 108906 (17.2 mm SL); MZUSP 108971 (13.2 mm SL); MZUSP 109008 (17.0 mm SL); USNM 225750 (13.7 mm SL); USNM 409823 (6, 16.3–18.5 mm SL; 2 C and S). Microcharacidium gnomus — MBUCV 21790 (20.2 mm SL); USNM 270150 (16.2 mm SL); USNM 270154 (2, 13.8–16.3 mm SL); USNM 270158 (3, 14.9–15.2 mm SL); USNM 285676 (19.7 mm SL); USNM 296519 (5, 15.1–17.2 mm SL; 2 C and S); USNM 322083 (3, 15.3–17.6 mm SL). Microcharacidium weitzmani — ANSP 159783 (10.7 mm SL); Paratypes, ANSP 169031 (6, 9.0–9.6 mm SL); ANSP 177511 (10.2 mm SL; 1 C and S).
We thank L. Malabarba (UFRGS) for providing facilities to conduct the present study. We are also thankful to the following collections and their staff for access to facilities and loans of the specimens used in the present study: M.H. Sabaj Pérez (ANSP), L.H. Rapp Py-Daniel (INPA), F. Provenzano (MBUCV), S. Fisch-Muller and R. Covain (MHNG), P.A. Buckup (MNRJ), W. Wosiacki (MPEG), A. Datovo and M.C. Cardoso de Pinna (MZUSP), and J. Williams (USNM). L.S.V. was financially supported by CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico; proc. n° 133586/2017-0).
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Laboratório de Ictiologia, Departamento de Zoologia, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9500, 91501-970, Porto Alegre, Rio Grande do Sul, Brazil.
Laboratório de Ictiologia, Departamento de Zoologia, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9500, 91501-970, Porto Alegre, Rio Grande do Sul, Brazil.
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L.S.Vieira and A.L.Netto-Ferreira. 2021. A new species of Microcharacidium (Characiformes: Crenuchidae) from the Central Amazon, Brazil. Canadian Journal of Zoology.
99(1): 57-61. https://doi.org/10.1139/cjz-2020-0138
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