Microcharacidium bombioides, Vieira & Netto-Ferreira, 2021

Vieira, L. S. & Netto-Ferreira, A. L., 2021, A new species of Microcharacidium (Characiformes: Crenuchidae) from the Central Amazon, Brazil, Can. J. Zool 99, pp. 57-61 : 58-60

Microcharacidium bombioides sp. nov.

Fig.1 ; Table 1

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).

ZOOBANK LSID: urn:lsid:zoobank.org:ato:F2C9E68A-953C-48FC-B25E-4C75CD079AE9.

HOLOTYPE: 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 .

PARATYPES: 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 .

DIAGNOSIS: 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).

DESCRIPTION: 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 pectoralfin 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 analfin, 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.

SEXUAL DIMORPHISM: No secondary sexually dimorphic character was observed among specimens of M. bombioides , although ripe female specimens may present a discretely deeper body.

DISTRIBUTION: The new species is widely distributed in the middle Rio Amazonas and its tributaries Rio Negro, Rio Trombetas, and Rio Tapajós ( Fig. 2 ).

ETYMOLOGY: 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.

Remarks

The inclusion of M. bombioides in the genus Microcharacidium is justified herein because the new species presents all four

synapomorphies proposed by Buckup (1993 b) 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 (1993 c) 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.

Figures

Fig. 1. Microcharacidium bombioides sp. nov., holotype. 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.

Fig. 2. Map of northern portion of South America showing the distribution of Microcharacidium bombioides sp. nov. The star represents the type locality. Circles may represent more than one collection event. Figure was created using QGIS version 2.18.0 and assembled from the data sources (shapefiles) of the IBGE (Instituto Brasileiro de Geografia e Estatística).