Aphyocharax pusillus Guenther , 1868

de Brito, Pamella Silva, Guimaraes, Erick Cristofore, Katz, Axel Makay, Piorski, Nivaldo Magalhaes & Ottoni, Felipe Polivanov, 2018, Taxonomic status of Aphyocharaxavary Fowler, 1913, Aphyocharaxpusillus Guenther, 1868 and Chirodonalburnus Guenther, 1869 (Characiformes, Characidae), Zoosystematics and Evolution 94 (2), pp. 393-399 : 393

Aphyocharax pusillus Guenther, 1868

Aphyocharax pusillus Günther, 1868: 480. Type locality: Huallaga and Xeberos [Amazon River Basin, Peru]. Syntypes: (1) BMNH 1867.6.13.46, (2) BMNH 1867.6.13.58-59.

Chirodon alburnus Günther, 1869:424: Type locality: Peruvian Amazons [Amazon River Basin, Peru]. Lectotype: BMNH 1869.5.21.10; Paralectotypes: (3) BMNH 1869.5.21.11-13. New synonym.

Material examined.

BMNH 1867.6.13.46, 1 (Syntype), Huallaga and Xeberos [Amazon River Basin, Peru], Mr. Bartlett. BMNH 1867.6.13.58-59, 2 (Syntypes), Huallaga and Xeberos [Amazon River Basin, Peru], Mr. Bartlett. BMNH 1869.5.21.10, 1 (Lectotype of Chirodon alburnus ), [Amazon River, Peru]. BMNH 1869.5.21.11-13, 3 (Paralectotypes of Chirodon alburnus ), [Amazon River, Peru].

Diagnosis.

Aphyocharax pusillus differs from all of its congeners, except A. avary , by having black or dark brown middle caudal-fin rays (Figs 1-3; Günther 1869, fig. 2). Aphyocharax pusillus is distinguished from A. avary by having fewer maxillary teeth, spread along the proximal half of the bone (Fig. 4 B–G) [vs. more maxillary teeth spread along 2/3 of the maxillary extension (Fig. 4A].

Morphological notes.

Meristic data of the type specimens are presented in Table 1. Body shape generally fusiform, slightly elongate, greatest body depth slightly anterior to dorsal-fin base. Dorsal body profile straight or slightly convex from snout to vertical through anterior nostrils; straight or slightly convex from posterior nostrils to tip of supraoccipital bone; straight or slightly convex from this point to dorsal-fin origin; slightly convex along dorsal-fin base; postdorsal profile straight from base of last dorsal-fin ray to adipose-fin origin; slightly concave from adipose-fin to end of caudal peduncle. Ventral profile convex from snout to pelvic-fin insertion; straight or slightly convex from this point to anal-fin origin; straight and posterodorsally-aligned along anal-fin base; postventral profile slightly concave from base of last anal-fin ray to end of caudal peduncle. Snout rounded. Mouth terminal, Lower jaw protrudes slightly beyond upper jaw when mouth closed; aligned approximately to middle of eye. Long and truncated snout, with its length larger than orbital diameter. Mouth terminal; upper jaw slightly larger than lower one. Maxillary bone surpassing a vertical line through middle of the eye; maxillary teeth small and conical, spread along proximal half of the bone. Lateral line interrupted; last scale on caudal-fin base.

There no mention of the presence of a humeral spot in the original description of either A. pusillus or C. alburnus . Additionally, the type materials of both species do not show any humeral spot. The illustration of C. alburnus by Günther (1869, fig. 2), however, gives the impression of the possible presence of a very inconspicuous humeral spot. However, the examination of recently preserved specimens of A. pusillus evidences that a very inconspicuous humeral spot could be present on larger recently preserved specimens (Fig. 3). Thus, we conclude that: it does not exhibit a humeral spot on smaller specimens or on specimens preserved several years ago; or it could possess a very inconspicuous humeral spot on larger and recently preserved specimens (Figs 1-3; Günther 1869, fig. 2). Nominal taxa have black or dark brown middle caudal-fin rays (Figs 1-3; Günther 1869, fig. 2).

Remarks.

Aphyocharax pusillus is the type species of the genus, designated by monotypy. The specimens were collected by Mr. Bartlett in Xeberos and Huallaga (Amazon River Basin, Peru), and succinctly described by Günther (1868); A. Günther did not, however, state the number of specimens used for the description. Eschmeyer et al. (2018) cite two lots as syntypes (BMNH 1867.6.13.46, 1 syntype, and BMNH 1867.6.13.58-59, 2 syntypes), and this material was examined in the present work.

Chirodon alburnus was succinctly described by Günther (1869) as belonging to the genus Chirodon Günther, 1864 because he overlooked the presence of maxillary teeth on the type specimens of C. alburnus . According to Maclaine (per. com.), Rosana Souza-Lima designated the specimens BMNH 1869.5.21.10 and BMNH 1869.5.21.11-13 as the lectotype and paralectotypes, respectively, of Chirodon alburnus in 2003, but that designation was never published. We concur, and so formally designate BMNH 1869.5.21.10 and BMNH 1869.5.21.11-13 as the lectotype and paralectotypes, respectively, of Chirodon alburnus .

Based on the information presented here (type material examination, original descriptions, and the literature) we conclude that Chirodon alburnus is a junior synonym of Aphyocharax pusillus - as there are no clear diagnostic character states that distinguish those two species. Additionally, the type locality of Chirodon alburnus is imprecise ("Peruvian Amazon"), encompassing the type locality of Aphyocharax pusillus .