A new miniature species of Odontocharacidium (Characiformes: Crenuchidae) from the Río Orinoco basin, Venezuela

Elizabeth Kathleen de Queiroz Rodrigues Andre L. Netto-Ferreira About the authors

ABSTRACT

A new species of Odontocharacidium is described from the upper Río Orinoco basin, in Venezuela. The new species is distinguished from its only congener, Odontocharacidium aphanes, by the presence of: the antorbital, the parietal branch of the supraorbital laterosensory canal, the postcleithrum 1, the conspicuous bars extending ventrally below the middle portion of the body posteriorly, and two dark round blotches at the tip of the caudal peduncle. With the recognition of an additional species of Odontocharacidium the diagnostic characters of the genus and the variability in the number of maxillary teeth in specimens are discussed.

Keywords:
Characidiinae; Miniaturization; Neotropics; Taxonomy; Teleostei

RESUMO

Uma nova espécie de Odontocharacidium é descrita para a bacia do alto rio Orinoco, na Venezuela. A nova espécie se distingue da sua única congênere, Odontocharacidium aphanes, pela presença: do antorbital, do ramo parietal do canal látero-sensorial supraorbital, do pós-cleitro 1, de barras conspícuas estendendo-se ventralmente à porção média do corpo e de duas manchas escuras e arredondadas na margem distal do pedúnculo caudal. Com o reconhecimento de uma espécie adicional de Odontocharacidium, são discutidos os caracteres diagnósticos do gênero e a variação no número de dentes maxilares nos espécimes.

Palavras-chave:
Characidiinae; Miniaturização; Neotrópico; Taxonomia; Teleostei

INTRODUCTION

Odontocharacidium Buckup is a miniature representative of the Crenuchidae, a moderately diverse Neotropical family containing 95 valid species distributed in 11 genera and two subfamilies (Fricke et al., 2020Fricke R, Eschmeyer WN, Fong JD. Species by family/subfamily in the Catalog of Fishe [Internet]. San Francisco: California Academy of Sciences; 2020. Avaible from: http://researcharchive.calacademy.org/research/ichthyology/catalog/SpeciesByFamily.asp
http://researcharchive.calacademy.org/re...
). The genus was erected to allocate its type species Klausewitzia aphanes Weitzman, Kanazawa as it was considered more closely related to the also miniature genera Microcharacidium Buckup and Elachocharax Myers, than to K. ritae Géry (the type species of Klausewitzia) in the sole phylogenetic study for the Crenuchidae (Buckup, 1993aBuckup PA. Phylogenetic interrelationships and reductive evolution in Neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics. 1993a; 9(3):305-41. https://doi.org/10.1111/j.1096-0031.1993.tb00227.x
https://doi.org/10.1111/j.1096-0031.1993...
). That close relationship between the three genera (clade EMO) was based on the lack of the parietal branch of supraorbital laterosensory canal; the absence of uroneurals; the presence of only conical teeth in both jaws; the incomplete lateral line; and the presence of a pair of dark blotches, located at the base of the dorsal and ventral caudal-fin lobes (Buckup, 1993aBuckup PA. Phylogenetic interrelationships and reductive evolution in Neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics. 1993a; 9(3):305-41. https://doi.org/10.1111/j.1096-0031.1993.tb00227.x
https://doi.org/10.1111/j.1096-0031.1993...
).

Odontocharacidium was diagnosed from the other crenuchids by: 1) absence of posttemporal; 2) absence of the supratemporal laterosensory canal; 3) absence of the pterotic laterosensory canal, and 4) pterotic, parietal and sphenotic lacking dermal portions between the semicircular canals, with the posttemporal fossa limited anteriorly by the sphenotic; 5) absence of postcleithrum 1 (Buckup, 1993bBuckup PA. Review of the characidiin fishes (Teleostei: Characiformes), with descriptions of four new genera and ten new species. Ichthyol Explor Fres. 1993b; 4(2):97-154.). In addition to these characters, the genus can be recognized by the lack of conspicuous dark pigmentation on the median portions of the pectoral and pelvic fin-rays, and the lack of a conspicuous black blotch on the posterior margin on the adipose fin (Buckup, van der Sleen, 2018Buckup PA, van der Sleen P. Family Crenuchidae-South American darters. In: van der Sleen P, Albert JS, editors. Field guide to the fishes of the Amazon, Orinoco, and Guianas. New Jersey: Princeton University Press; 2018. p.142-48.). To date, the genus included only its type species, Odontocharacidium aphanes (Weitzman, Kanazawa) from the rio Negro in the Amazon basin (Weitzman, Kanazawa, 1977Weitzman SH, Kanazawa RH. A new species of pygmy characoid fish from the Rio Negro and Rio Amazonas, South America (Teleostei: Characidae). P Biol Soc Wash. 1977; 90(1):149-60. Avaible from: https://www.biodiversitylibrary.org/page/39057897#page/173/mode/1up
https://www.biodiversitylibrary.org/page...
), but during a revisionary study of the genus, a new species from the Río Orinoco in Venezuela was detected among museum samples, and is described herein.

MATERIAL AND METHODS

Counts and measurements follow Buckup (1993bBuckup PA. Review of the characidiin fishes (Teleostei: Characiformes), with descriptions of four new genera and ten new species. Ichthyol Explor Fres. 1993b; 4(2):97-154.). Measurements were made from photographs of the left side of specimens, with aid of the software Axion Vision 4.8. 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). The values for each meristic data in the description are followed by their frequency in parentheses with an asterisk indicating the values for the holotype. Counts of vertebrae, supraneurals, branchiostegal rays, and teeth were obtained from cleared and stained (c&s) specimens prepared according to Taylor, Van Dyke (1985Taylor WR, Van Dyke GC. Revised procedures for staining and clearing small fishes and other vertebrates for bone and cartilage study. Cybium. 1985; 9(2):107-19. Avaible from: http://sfi-cybium.fr/en/node/2423
http://sfi-cybium.fr/en/node/2423...
). Vertebrae of the Weberian apparatus were counted as four precaudal elements, and the fused PU1+U1 of the caudal region as a single element. Specimens were sexed macroscopically through a small incision on the right side of the body for gonad inspection.

Institutional abbreviations are Academy of Natural Sciences of the Drexel University (ANSP), Field Museum of Natural History (FMHN), Instituto Nacional de Pesquisas da Amazônia (INPA), Laboratório de Biologia e Genética de Peixes (LBP), Museo de Historia Natural La Salle (MHNLS), Museu Paraense Emílio Goeldi (MPEG), Museu de Zoologia da Universidade de São Paulo (MZUSP), and National Museum of Natural History/Smithsonian Institution (USNM).

RESULTS

Odontocharacidium varii, new species

urn:lsid:zoobank.org:act:44171E14-9E40-4960-ACAE-26896C655D3F

(Fig. 1; Tab. 1)

Odontocharacidium aphanes (not Weitzman, Kanazawa, 1977Weitzman SH, Kanazawa RH. A new species of pygmy characoid fish from the Rio Negro and Rio Amazonas, South America (Teleostei: Characidae). P Biol Soc Wash. 1977; 90(1):149-60. Avaible from: https://www.biodiversitylibrary.org/page/39057897#page/173/mode/1up
https://www.biodiversitylibrary.org/page...
). -Buckup, 1993aBuckup PA. Phylogenetic interrelationships and reductive evolution in Neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics. 1993a; 9(3):305-41. https://doi.org/10.1111/j.1096-0031.1993.tb00227.x
https://doi.org/10.1111/j.1096-0031.1993...
:305-41 (phylogenetic study of Characidiinae). -Buckup, 1993bBuckup PA. Review of the characidiin fishes (Teleostei: Characiformes), with descriptions of four new genera and ten new species. Ichthyol Explor Fres. 1993b; 4(2):97-154.:136 (description of Odontocharacidium; distribution). -Buckup, 2003Buckup PA. Family Crenuchidae (South American Darters). In: Reis RE, Kullander SO, Ferraris CJJ, editors. Check list of the freshwater fishes of South and Central America. Porto Alegre: Edipucrs; 2003. p.87-95.:93 (Checklist; occurrence in Venezuela). -Buckup, van der Sleen, 2018Buckup PA, van der Sleen P. Family Crenuchidae-South American darters. In: van der Sleen P, Albert JS, editors. Field guide to the fishes of the Amazon, Orinoco, and Guianas. New Jersey: Princeton University Press; 2018. p.142-48.:147 (Field guide; distribution).

Holotype. MHNLS 26156, 14.7 mm SL, Venezuela, Río Negro Municipality, Río Orinoco, Caño Chola, where it crosses the road from San Carlos de Río Negro to Solano, 1°58’00”N 67°00’00”W, 11 Apr 1985, R.P. Vari.

Paratypes. All from Venezuela, Amazonas: ANSP 161317, 8, 14.3-15.8 mm SL, Venezuela, Amazonas, Cano Caño entering eastern side of Río Casiquiare ca. 7.0 km approx. downstream from mouth of Río Pamoni, 2°48’00”N 65°58’00”W, 20 Mar 1987, B. Chernoff, S.W.G. Lopes, J. Fernandez, O. Castillo, M.E Antonio. FMNH 105971, 4, 12.7-12.8 mm SL, Venezuela, Território Federal Amazonas [Currently Estado Amazonas], Caño Curcutito about. 1 km upstream mouth in Río Autana, 4°43’48”N 67°37’12”W, 11 Feb 1992, B. Chernoff, A. Machado-Allison, J. A Wheeler, J. Fernandez, N. M. Gotschall. USNM 270149, 21, 14.1-16.6 mm SL (2 c&s), 14.8-15.8 mm SL, collected with holotype.

FIGURE 1
| Odontocharacidium varii, new species, A. Holotype, MHNLS 26156, 14.7 mm SL, Venezuela, Río Negro Municipality, Río Orinoco; Paratype, USNM 270149, 14.3 mm SL, Venezuela, Río Negro Municipality, Río Orinoco. Scale bar = 1 mm.

Diagnosis. Odontocharacidium varii differs from O. aphanes by the presence of the antorbital (vs. antorbital absent); the presence of the supraorbital laterosensory canal (vs. canal absent); the presence of postcleithrum 1 (vs. postcleithrum 1 absent); the presence of conspicuous bars extending ventrally to the middle portion of the body (vs. bars restricted to the dorsal portion of the body); and the presence of two dark round blotches located at the tip of caudal peduncle (vs. blotches absent).

Description. Morphometric data for the holotype and paratypes, Tab.1. Body short, relatively compressed. Dorsal profile convex from snout tip to dorsal-fin terminus, slightly concave or nearly straight from that point to insertion of anteriormost dorsal caudal-fin procurrent rays. Ventral profile convex from lower lip to pelvic-fin insertion, moderately convex from that point to anal-fin origin, becoming slightly concave from that point to insertion of first ventral procurrent caudal-fin ray.

TABLE 1
| Morphometrics of Odontocharacidium varii. Number of individuals (20), mean, minimum (Min), maximum (Max) and standard deviation (SD) include values of the holotype.

Mouth small, terminal. Teeth on both jaws conical, Fig. 2. Premaxilla with single row of 9(1) or 10(1) teeth decreasing in size laterally. Maxilla reaching vertical through anterior margin of orbit. Maxilla with 9(1) or 10(1) teeth along entire ventral edge, Fig. 2. Dentary with two series of teeth, outer series with 8(2), inner series with 9(1) or 12(1). Ectopterygoid teeth 6(1) or 7(1). Endopterygoid edentulous. Nostrils round distinctly separated by fleshy bridge without dermal flaps. Posterior nostril closer to orbit and slightly larger than anterior nostril. Small cranial fontanel bordered by supraoccipital, parietal and frontal. Branchiostegal rays 4(2); 3(2) in the anterior ceratohyal, and 1(2) between the anterior ceratohyal and posterior ceratohyal. Antorbital present. Parietal branch of supraorbital laterosensory canal present.

FIGURE 2
| Odontocharacidium varii, new species, USNM 270149, paratype, 15.8 mm SL, Venezuela, Río Negro Municipality, Río Orinoco. Lateral view of mandibular arch and dentition, flipped right side, anterior to left.

Scales cycloid. Lateral line longitudinal series with 29(1), 30*(5), 31(7), 32(3) or 33(2) scales, of which 4(6), 5*(8) or 6(2) are perforated. Longitudinal series above lateral line 3(18) or 4*(2); and 4*(17) or 5(2) below. Predorsal scales 6(1), 7*(10) or 8(9). Isthmus completely scaled. Circumpeduncular scales 12*(20).

Pectoral-fin total rays 7(1), 8(5) or 9*(14), second and third rays longest. Tip of adpressed pectoral fin not reaching pelvic-fin origin. Postcleitrum 1 present. Pelvic-fin total rays 8(3), 9*(14) or 10(2); first, second and third rays longest. Longest pelvic-fin rays reaching vertical through anal-fin origin. Supraneurals 4(2), anterior to neural spines of vertebral centra 5-8(2). Dorsal-fin rays ii,9*(22); second and third rays longest; first pterygiophore anterior to neural spine of centrum 9(2). Adipose fin present or absent, present in holotype. Anal-fin rays ii,5(5), ii,6*(6) or ii,7(9); third and fourth rays longest; first pterygiophore anterior to haemal spine of centrum 20(1) or 21(1). Caudal-fin principal rays 10/8(1) or 10/9*(21). Hypural 6 present. Precaudal vertebrae 17(2), caudal 15(2); total vertebrae 32(2).

Coloration in alcohol. Background color of head and body pale yellow. Dark brown chromatophores scattered on sides of head. Chromatophores conspicuously concentrated on upper lip, with area between nostrils forming diffuse band. Small concentration of chromatophores from lower lip to near terminus of maxilla. Concentration of chromatophores forming dark triangular suborbital blotch. Dorsal profile of head and posterior margin of orbit with scattered chromatophores forming light brown pigmentation. Dorsal portion of head conspicuously more pigmented than lateral portions. Opercular membrane hyaline.

Humeral blotch present, conspicuous. Vertical bars on dorsal portion of body 6(2), 7(8), 8*(7) or 9(3); bars anterior to insertion of dorsal fin 2*(19) or 3(1); 2*(20) along dorsal-fin base; 3(1), 4*(16) or 5(3) between dorsal-fin terminus and distal tip of caudal peduncle. Bars reaching beyond the midline portion of the body ventrally usually between pelvic-fin and anal-fin origins, with posterior most four bars reaching ventral portion of body. Horizontal septum intermittently pigmented, forming series of thin, dark dashes from pectoral girdle to near tip of caudal peduncle. Ventral portion with concentration of chromatophores on mid-ventral scales forming three thin dark bands at pelvic-fin origin, near anus and at anal-fin base. Caudal peduncle with two dark round blotches at base of each caudal-fin lobe. Pectoral, pelvic, anal and caudal fins hyaline with scattered chromatophores at distal tips. Dorsal fin with concentration of chromatophores forming two discrete horizontal bands, one at middle of in rays and the other at distal tip.

Sexual dimorphism. Dissection of paratypes of Odontocharacidium varii for gonad inspection failed to unambiguously determine sex of available specimens, as gonads of all examined specimens seemed to be immature or in resting stages. Additionally, no distinguishable external secondary sexually dimorphic characters were observed in those specimens.

Geographical distribution. Odontocharacidium varii is known from the upper portion of the Río Orinoco, Fig. 3.

FIGURE 3
| Map of geographical distribution of Odontocharacidium varii (circles). Type-locality represented by the same symbol in white color.

Etymology. The specific epithet is in honor to Richard P. Vari, first collector of the new species and constant professional inspiration to the authors. A noun in genitive.

Conservation status. Odontocharacidium varii is known from three different localities in the upper Río Orinoco basin. Although none of the sampling sites is within preservation areas, those appear to be well preserved. Besides, there are several national parks and indigenous areas surrounding the known area of occurrence of the species, suggesting the lack of significant threats to the conservation of the species. Therefore, Odontocharacidium varii can be classified herein as a Least Concern (LC) species according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN, 2019International Union for Conservation of Nature (IUCN). Standards and Petitions Subcommittee. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14 [Internet]. 2019. Available from: https://nc.iucnredlist.org/redlist/content/attachment_files/RedListGuidelines.pdf
https://nc.iucnredlist.org/redlist/conte...
).

Remarks. Odontocharacidium varii present a slight variation of color pattern, with some specimens having it more pronounced than others. The bands, bars and the humeral blotch can vary in intensity among specimens from the same lot, Fig. 1. It is unclear at this moment if this phenomenon is indicative of intraspecific variation or coloration fading of the specimens. Nevertheless, both limits of the variation range allow unambiguous distinction between specimens of O. varii from O. aphanes.

Comparative material examined. Brazil, Rio Negro: MZUSP 12978, 1, 13.4 mm SL (holotype of Odontocharacidium aphanesWeitzman & Kanazawa, 1977Weitzman SH, Kanazawa RH. A new species of pygmy characoid fish from the Rio Negro and Rio Amazonas, South America (Teleostei: Characidae). P Biol Soc Wash. 1977; 90(1):149-60. Avaible from: https://www.biodiversitylibrary.org/page/39057897#page/173/mode/1up
https://www.biodiversitylibrary.org/page...
). MZUSP 12979, 3, 11.4-13.0 mm SL (paratypes of Odontocharacidium aphanes). MZUSP 109657, 2, 12.3-11.8 mm SL. MPEG 25491, 2, 14.6-16.2 mm SL. Rio Branco: INPA 39429, 2, 13.1-12.4 mm SL. MZUSP 113270, 3, 10.1-10.3 mm SL. MZUSP 113665, 36, 10.8-13.3 mm SL. LBP 15115, 12, 14.1-15.9 mm SL, 1 c&s, 14.6 mm SL. LBP 15114, 8, 15-16.1 mm SL, 1 c&s, 14.7 mm SL.

DISCUSSION

The close relationship between Odontocharacidium varii and O. aphanes is proposed herein as both species share most diagnostics characters hypothesized by Buckup (1993bBuckup PA. Review of the characidiin fishes (Teleostei: Characiformes), with descriptions of four new genera and ten new species. Ichthyol Explor Fres. 1993b; 4(2):97-154.) as defining the genus: 1) absence of the posttemporal; 2) absence of the the supratemporal sensory canal; 3) absence of the pterotic sensory canal, and 4) pterotic, parietal and sphenotic lacking dermal portions between the semicircular canals, with the posttemporal fossa limited anteriorly by the sphenotic; 5) absence of postcleithrum 1 (Buckup 1993bBuckup PA. Review of the characidiin fishes (Teleostei: Characiformes), with descriptions of four new genera and ten new species. Ichthyol Explor Fres. 1993b; 4(2):97-154.). Conversely, unlike O. aphanes, the specimens of Odontocharacidium varii examined herein present a bilaterally symmetric postcleithrum 1, an antorbital and the parietal branch of supraorbital laterosensory canal, conditions absent in O. aphanes. The sharing of four out of five exclusive characters defining Odontocharacidium justifies not only the inclusion of the species described herein in the genus, but also to re-diagnose the genus, based only on the absence of the posttemporal, the absence of the the supratemporal sensory canal, the absence of the pterotic sensory canal, and the lack of dermal portions on the pterotic, parietal and sphenotic between the semicircular canals, with the posttemporal fossa limited anteriorly by the sphenotic.

The diagnostic features of Odontocharacidium proposed by Buckup (1993bBuckup PA. Review of the characidiin fishes (Teleostei: Characiformes), with descriptions of four new genera and ten new species. Ichthyol Explor Fres. 1993b; 4(2):97-154.) and reviewed herein seem to represent developmental truncations, associated to the miniaturization process, which usually leads to losses and simplifications of dermal bones (i.e. posttemporal and postcleithra) or dermal portions of composite bones (i.e. pterotic and sphenotic) (Britz, Conway, 2009Britz R, Conway KW. Osteology of Paedocypris, a miniature and highly developmentally truncated fish (Teleostei: Ostariophysi: Cyprinidae). J Morphol. 2009; 270(4):389-412. https://doi.org/10.1002/jmor.10698
https://doi.org/10.1002/jmor.10698...
; Britz et al., 2009Britz R, Conway KW, Rüber L. Spectacular morphological novelty in a miniature cyprinid fish, Danionella dracula n. sp. Proc R Soc B. 2009; 276(1665):2179-86.; Toledo-Piza et al., 2014Toledo-Piza M, Mattox GM, Britz R. Priocharax nanus, a new miniature characid from the rio Negro, Amazon basin (Ostariophysi: Characiformes), with an updated list of miniature Neotropical freshwater fishes. Neotrop Ichthyol. 2014; 12(2):229-46. http://dx.doi.org/10.1590/1982-0224-20130171
http://dx.doi.org/10.1590/1982-0224-2013...
; Mattox et al., 2016Mattox GM, Britz R, Toledo‐Piza M. Osteology of Priocharax and remarkable developmental truncation in a miniature Amazonian fish (Teleostei: Characiformes: Characidae). J Morphol . 2016; 277(1):65-85. https://doi.org/10.1002/jmor.20477
https://doi.org/10.1002/jmor.20477...
). Although no mature specimens of Odontocharacidium varii were detected in the present study, none of the 34 representatives of the species examined herein is larger than 17 mm SL, suggesting a size range similar to that of O. aphanes for O. varii. The new species would, therefore, fit the criteria established by Weitzman, Vari (1988Weitzman SH, Vari RP. Miniaturization in South American freshwater fishes; an overview and discussion. P Biol Soc Wash . 1988; 101(2):444-65. Avaible from: https://ia800207.us.archive.org/31/items/biostor-77854/biostor-77854.pdf
https://ia800207.us.archive.org/31/items...
) to consider this species a miniature, bringing the number of miniaturized crenuchids to 17 (Toledo-Piza et al., 2014Toledo-Piza M, Mattox GM, Britz R. Priocharax nanus, a new miniature characid from the rio Negro, Amazon basin (Ostariophysi: Characiformes), with an updated list of miniature Neotropical freshwater fishes. Neotrop Ichthyol. 2014; 12(2):229-46. http://dx.doi.org/10.1590/1982-0224-20130171
http://dx.doi.org/10.1590/1982-0224-2013...
; Mendonça, Netto-Ferreira 2015Mendonça MB, Netto-Ferreira AL. New Species of Characidium (Characiformes: Crenuchidae) From the Rio Tapajós and Rio Xingu Drainages, Pará, Brazil. Zootaxa. 2015; 4021(1):187-94. http://dx.doi.org/10.11646/zootaxa.4021.1.9
http://dx.doi.org/10.11646/zootaxa.4021....
).

Although Buckup (1993aBuckup PA. Phylogenetic interrelationships and reductive evolution in Neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics. 1993a; 9(3):305-41. https://doi.org/10.1111/j.1096-0031.1993.tb00227.x
https://doi.org/10.1111/j.1096-0031.1993...
) considered the absence of the parietal branch of the supraorbital canal as a synapomorphy for the clade including Elachocharax, Microcharacidium and Odontocharacidium (EMO), representatives of the new species described herein present a small bony tube branching from the supraorbital laterosensory canal, topologically similar to that illustrated by Buckup (1993cBuckup PA. The monophyly of the Characidiinae, a Neotropical group of characiform fishes (Teleostei: Ostariophysi). Zool J Linnean Soc. 1993c; 108:225-45.) for Characidium fasciatum Reinhardt, and by Weitzman (1962Weitzman SH. The osteology of Brycon meeki, a generalized characid fish, with an osteological definition of the family. Stanford Ichth Bull. 1962; 8:1-77.) for Brycon meeki Eigenmann, Hildebrand, and attributed as the parietal branch of the supraorbital canal. Representatives of O. aphanes and species of Microcharacidium, on the other hand, indeed lack any branching on the supraorbital canal as described by that author, and the presence of that condition in O. varii may be considered a reversal. Likewise, the pair of dark blotches at the base of each caudal-fin lobe, also hypothesized as synapomorphic of the aforementioned clade containing the three genera seems to have been secondarily lost in Odontocharacidium aphanes. Buckup (1993aBuckup PA. Phylogenetic interrelationships and reductive evolution in Neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics. 1993a; 9(3):305-41. https://doi.org/10.1111/j.1096-0031.1993.tb00227.x
https://doi.org/10.1111/j.1096-0031.1993...
) considered this character as present in O. aphanes, but in fact, such interpretation was actually based on specimens of the lot USNM 270149, herein recognized as Odontocharacidium varii (see synonymy list).

Weitzman, Kanazawa (1977Weitzman SH, Kanazawa RH. A new species of pygmy characoid fish from the Rio Negro and Rio Amazonas, South America (Teleostei: Characidae). P Biol Soc Wash. 1977; 90(1):149-60. Avaible from: https://www.biodiversitylibrary.org/page/39057897#page/173/mode/1up
https://www.biodiversitylibrary.org/page...
) observed a conspicuous variability in the number of maxillary teeth (9 to 17), when describing Odontocharacidium aphanes. The examination of specimens of O. aphanes herein resulted in a slightly greater variation (3 to 15), although no specimens with more than 15 teeth were found. Within that variation, some specimens seem to present consistently teeth restricted to the anterior portion of the maxilla, whereas other specimens usually have teeth covering the entire ventral surface of the bone. Unlike O. aphanes, all examined representatives of O. varii have teeth along the entire ventral edge of the maxilla, Fig. 2. A similar condition was described associated with sexual dimorphism in Copella and Pyrrhulina members of the Lebiasinidae (Netto-Ferreira, Marinho, 2013Netto-Ferreira AL, Marinho MMF. New species of Pyrrhulina (Ostariophysi: Characiformes: Lebiasinidae) from the Brazilian Shield, with comments on a putative monophyletic group of species in the genus. Zootaxa. 2013; 3664(3):369-76. http://dx.doi.org/10.11646/zootaxa.3664.3.7
http://dx.doi.org/10.11646/zootaxa.3664....
; Marinho, Menezes, 2017Marinho MMF, Menezes NA. Taxonomic review of Copella (Characiformes: Lebiasinidae) with an identification key for the species. PLoS One. 2017; 12(8):e0183069. https://doi.org/10.1371/journal.pone.0183069
https://doi.org/10.1371/journal.pone.018...
; Vieira, Netto-Ferreira, 2019Vieira LS, Netto-Ferreira AL. New species of Pyrrhulina (Teleostei: Characiformes: Lebiasinidae) from the eastern Amazon, Pará, Brazil. Neotrop Ichthyol . 2019; 17(2): e190013. http://dx.doi.org/10.1590/1982-0224-20190013
http://dx.doi.org/10.1590/1982-0224-2019...
).

To this moment, Odontocharacidium varii had been confused with O. aphanes in collections and by Buckup (1993aBuckup PA. Phylogenetic interrelationships and reductive evolution in Neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics. 1993a; 9(3):305-41. https://doi.org/10.1111/j.1096-0031.1993.tb00227.x
https://doi.org/10.1111/j.1096-0031.1993...
,b), who examined the specimens from Caño Chola (USNM 270149). Such misidentification may have been induced by the distinctive overall morphology of Odontocharacidium among Characidiinae, besides the diminutive size of the specimens, which can be considered an additional difficulty in detecting the variation among different populations or species in the genus. Considering the minute size of the representatives of the genus, and the lack of taxonomic studies subsequent to those of Buckup (1993aBuckup PA. Phylogenetic interrelationships and reductive evolution in Neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics. 1993a; 9(3):305-41. https://doi.org/10.1111/j.1096-0031.1993.tb00227.x
https://doi.org/10.1111/j.1096-0031.1993...
), it is likely that the species richness in Odontocharacidium and other miniature Crenuchidae may be considerably underestimated and pending formal description, as was recently observed by (Toledo-Piza et al., 2014Toledo-Piza M, Mattox GM, Britz R. Priocharax nanus, a new miniature characid from the rio Negro, Amazon basin (Ostariophysi: Characiformes), with an updated list of miniature Neotropical freshwater fishes. Neotrop Ichthyol. 2014; 12(2):229-46. http://dx.doi.org/10.1590/1982-0224-20130171
http://dx.doi.org/10.1590/1982-0224-2013...
; Mattox et al., 2016Mattox GM, Britz R, Toledo‐Piza M. Osteology of Priocharax and remarkable developmental truncation in a miniature Amazonian fish (Teleostei: Characiformes: Characidae). J Morphol . 2016; 277(1):65-85. https://doi.org/10.1002/jmor.20477
https://doi.org/10.1002/jmor.20477...
) for the heterocharacin Priocharax Weitzman, Vari.

ACKNOWLEDGMENTS

Authors are thankful to Mark Sabaj and Mariangeles Arce (ANSP), Caleb McMahan and Susan Mochel (FMNH), Lúcia Rapp Py-Daniel (INPA), Claudio Oliveira (LBP), Carlos Lucena and Margarete Lucena (MCP), Oscar Lasso-Alcalá (MHNLS), Wolmar Wosiacki (MPEG), Alessio Datovo (MZUSP), Jeffrey Williams (USNM), for support during visits and loan of specimens. Authors are also thankful to Alberto Akama (MPEG), Claudio Oliveira (UNESP), Luiz Malabarba (UFRGS) and Wolmar Wosiacki (MPEG) for providing space and facilities during early stages of this project. This paper is part of the Masters dissertation of EKQR, with the financial support of master’s degree fellowship by CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico; proc. n° 130950/2016-5), at the Programa de Pós-Graduação em Zoologia UFPA/MPEG.

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ADDITIONAL NOTES

  • HOW TO CITE THIS ARTICLE

    Rodrigues EKQ, Netto-Ferreira AL. A new miniature species of Odontocharacidium (Characiformes: Crenuchidae) from the Río Orinoco basin, Venezuela. Neotrop Ichthyol. 2020; 18(2):e190008. https://doi.org/10.1590/1982-0224-2019-0008
  • ZOOBANK REGISTER

    urn:lsid:zoobank.org:pub:B0636035-2139-4110-8F00-45C9CED4C990

Publication Dates

  • Publication in this collection
    26 June 2020
  • Date of issue
    2020

History

  • Received
    06 Nov 2019
  • Accepted
    06 May 2020
Sociedade Brasileira de Ictiologia Universidade Estadual de Maringá, Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura/Coleção Ictiologia, Av. Colombo, 5790, 87020-900 Maringá, PR, Brasil, Tel.: (55 44)3011 4632 - Maringá - PR - Brazil
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