Xenurobrycon varii, Mendonça & Peixoto & Dutra & Netto-Ferreira¹, 2016

Mendonça, Marina Barreira, Peixoto, Luiz Antônio Wanderley, Dutra, Guilherme Moreira & Netto-Ferreira, André Luiz, 2016, A new miniature of Xenurobryconini (Characiformes: Characidae) from the rio Tapajós basin, Brazil, Neotropical Ichthyology (e 150057) 14 (1), pp. 1-8 : 2-7

Xenurobrycon varii , new species urn:lsid:zoobank.org:act:01A0735B-EB85-46F0-AA9E-ED8DE7234D37

Holotype. MPEG 32825 , male, 14.2 mm SL, Brazil, Pará, Jacareacanga, Vila de Mamãe Anã, tributary of rio Tapajós , 5°42’22”S 57°22’30”W, 19 Jan 2013, N. Benone.

Paratypes. All from Brazil, Pará, Jacareacanga, rio Tapajós basin : INPA 48819 , 3 males (12.5-14.0 mm SL), 7 females or immatures (11.1-13.7 mm SL), collected with holotype . MCNIP 1678 , 3 males (12.5-13.5 mm SL), 7 females or immatures (11.4-13.4 mm SL), rio Tapajós basin, near Vila de Mamãe Anã , 05°42’23.5”S 57°22’31.9”W, 2 Oct 2012, N. Benone . MPEG 25239 , 9 males (13.1-13.4 mm SL; 3 c&s), 45 females or immatures (8.4-13.9 mm SL; 3 c&s), same data as MCNIP 1678. MPEG 25240 , 2 females or immatures (13.1-14.6 mm SL), near Vila de São Martins , 06°05’59.7”S 57°39’11.0”W, 9 Oct 2012, N. Benone . MPEG 25242 , 1 male (15.3 mm SL), 2 females or immatures (13.4-13.5 mm SL), near Vila de Penedo , 05°36’40.4”S 57°07’16.6”W, 12 Oct 2012, N. Benone . MPEG 25271 , 22 females or immatures (10.3-13.2 mm SL), near Vila de Mamãe Anã , 4 Dec 2012, N. Benone . MPEG 26592 , 29 males (12.9-14.3 mm SL; 3 c&s), 47 females or immatures (10.2-14.4 mm SL; 3 c&s), collected with holotype . MPEG 26593 , 2 males (16.3- 16 mm SL), 2 females or immatures (15.9-16.8 mm SL), Vila de Penedo , 5°36’40”S 57°7’16”W, 16 Jan 2013, N. Benone . MPEG 26594 , 13 males (15.0- 15.7 mm SL; 2 c&s), 16 females (14.4-16.51 mm SL), Vila de Buburé , 4°44’10”S 56°37’19”W, 07 Jan 2013, N. Benone . MPEG 26595 , 3 males (15.8-16.0 mm SL), 3 females or immatures (15.2-15.6 mm SL), Vila de Buburé , 4°42’58”S 56°26’24”W, 6 Jan 2013, N. Benone . MPEG 27749 , 17 males (13.1-14.5 mm SL), 33 females or immatures (9.5-15.0 mm SL), Vila de Mamãe Anã , 5°42’21.6”S 57°22’30.0”W, 26 Mar 2013 , T. Begot. MPEG 27875 , 3 females or immatures (11.2-12.5 mm SL), Vila de São Martins , 6°06’S 57°39’W, 29 Mar 2913 , T. Begot. MPEG 27920 , 2 females or immatures (11.3-12.4 mm SL), Vila de Mamãe Anã , 5°47’49.2”S 57°24’7.2”W, 28 Mar 2013 , T. Begot. MPEG 27937 , 3 females or immatures (10.1-11.6 mm SL), Vila de Jatobá , 5°03’50.4”S 56°51’46.80”W, 19 Mar 2013 , T. Begot. MPEG 28439 , 1 female or immature (12.8 mm SL), Vila de São Martins , 6°06’22.0”S 57°39’25.2”W, 3 Sep 2013, Ambiental Concremat team . MPEG 28553 , 9 males (12.1- 14.6 mm SL), 8 females or immatures (11.3-12.9 mm SL), Vila de Mamãe Anã , 5°42’32.4”S 57°22’30”W, 28 Aug 2013, Ambiental Concremat team . MPEG 28589 , 1 female or immature, 12.3 mm SL, Vila de Penedo , 5°36’11.9”S 57°07’15.6”W, 25 Aug 2013, Ambiental Concremat team . MZUSP 117877 , 3 males (12.4-13.6 mm SL), 7 females or immatures (13.2-14.3 mm SL) ; USNM 436655 , 3 males (12.1-13.1 mm SL), 7 females or immatures (11.3-13.1 mm SL), collected with holotype .

Non-types. All from Brazil, Pará, rio Tapajós basin: MPEG 7692 , 6 females or immatures (12.2-13.5 mm SL), rio Santa Luzia , Trairão, 05°15’46”S 56°01’29” W, 12 Jun 2002 . MPEG 26591 , 6 males (15.0- 16.2 mm SL) , 3 females or immatures (14.9-17.3 mm SL), Vila de Mamãe Anã , 05°45’52”S 57°16’58”W, 18 Jan 2013 . MPEG 28453 , 2 females or immatures (11.1-13.2 mm SL), Vila de Mamãe Anã 5°46’48.4”S 57°17’23.9”W, 30 Aug 2013 .

Diagnosis. Xenurobrycon varii is readily distinguished from its congeners by the dark posterior half of both caudal-fin lobes (vs. hyaline) and the absence of infraorbitals 4 and 5 (vs. absence of infraobitals 1, 4 and 5 in X. coracoralinae Moreira and presence of infraorbitals 1-5 in X. heterodon Weitzman & Fink , X. macropus Myers & Miranda Ribeiro, X. polyancistrus Weitzman and X. pteropus Weitzman & Fink ). The new species is further differentiated from its congeners, except X. coracoralinae and X. macropus , by the presence of a set of lamellar processes on the eighth principal ray of the lower caudal-fin lobe ( Figs. 3a, 3b , vs. absence in X. heterodon , X. polyancistrus and X. pteropus ). The new species differs from X. coracoralinae by the presence of hooks on the last unbranched plus the first 9 th- 12 th branched anal-fin rays of mature males ( Fig. 4a, 4b , vs. hooks present only on last unbranched and first 4 th- 5 th branched rays). Xenurobrycon varii can be additionally distinguished from X. heterodon by the presence of only conical dentary teeth ( Fig. 5 vs. anterior dentary teeth tricuspid). The new species is also differentiated from X. polyancistrus by the posterior anal-fin hooks approximately equal or reduced in size posteriorly in mature males ( Fig. 4a, 4b , vs. posterior larger anal-fin hooks). Finally, it further differs from X. pteropus by the absence of adipose-fin (vs. presence) and greater number of predorsal scales (15-18 vs. 13).

and becoming almost completely straight from terminus of dorsal-fin to first dorsal procurrent caudal-fin ray. Ventral profile of head convex from lower lip to pectoral-fin origin. Ventral profile of body slightly convex from that point to anterior margin of urogenital papillae, straightening out along anal-fin base, and becoming slightly convex from anal-fin terminus to first ventral procurrent caudal-fin rays. Description. Morphometric data for examined specimens in Table 1. Body profile convex along dorsal portion from tip of snout to posterior end of supraoccipital spine; slightly convex from that point to dorsal-fin origin (more prominent in females) approximately straight along dorsal-fin base,

Mouth terminal; upper and lower jaws of equal length. Teeth conical with slightly posteriorly recurved tips. Premaxillary teeth 8(2), 9(4), 10(2) or 11(3). Maxillary teeth 7(6) or 8(6). Posterior tip of maxilla reaching anterior margin of lateral ethmoid. Dentary teeth 11(3) or 12(1); second and sometimes third tooth anterodorsally aligned. Branchiostegal rays 4(12); first to third attached to anterior ceratohyal and fourth attached to cartilage between anterior and posterior ceratohyal (n=8) or to posterior ceratohyal (n=4). Only antorbital and infraorbitals 1, 2 and 3 present. Supraorbital, pterotic laterosensory canal and epioccipital bridge absent. Extrascapular and posttemporal bones absent. Supracleithrum laterosensory canal absent.

Scales cycloid, with few or no radii on posterior margin, except for pouch scale and scales between pelvic-fin origins (See “Sexual Dimorphism”). Predorsal scales 15(3), 16(16), 17*(12) or 18(2). Lateral line longitudinal series with 30(1), 31(3), 32(5), 33(5), 34*(8), 35(3), 36(4), 37(2) or 38(2) scales, of which 3(2), 4(10), 5*(10), 6(7) or 7(3) are perforated. Circumpeduncular scales 10(3), 11(4), 12*(25) or 13(1). Scale rows between dorsal- and anal-fin origins 8(1), 9*(11), 10(17) or 11(4).

Pectoral-fin rays i,7(8) or i,8*(25). Tip of pectoral fin reaching slightly beyond vertical through pelvic-fin origin in females; total pelvic-fin rays 7*(28) or 8(5) (see ‘‘Sexual Dimorphism”). Supraneurals absent. Dorsal-fin rays ii,6(6) or ii,7*(27). First dorsal-fin pterygiophore inserted immediately posterior to neural spine of 15 th (6) or 16 th (6) centrum. Dorsal-fin origin immediately posterior to anal-fin origin. Adipose fin absent. Anal-fin rays iii,13(2), iii,14(5), iii,15*(9), iii,16(12) or iii,17(5). First anal-fin pterygiophore inserted immediately posterior to haemal spine of 13 th (11) or 14 th (1) centrum. Mature males with anal-fin lobe longer than that of females and bilateral hooks on branched and unbranched rays (see “Sexual Dimorphism”). Principal caudal-fin rays 10/9; highly modified, and with bony hooks (see “Sexual Dimorphism”). Dorsal caudal-fin procurrent rays 5(10) or 6(2); ventral caudal-fin procurrent rays 6(9) or 7(3). Precaudal vertebrae 12(12). Caudal vertebrae 24(9) or 25(3).

Color in alcohol. Body pale yellow with small chromatophores on posterior margin of scales. Chromatophores highly concentrated on lips, but more disperse on dorsal portion of head, infraorbital and mandibular areas. Postorbital area with scattered chromatophores, more concentrated anteriorly to dark longitudinal stripe. Narrow, dark longitudinal stripe extending from fifth or sixth longitudinal scale to end of caudal peduncle. Narrow, dark dorsal stripe extending from posterior margin of supraoccipital to dorsal caudal-fin procurrent rays, whitish at dorsal fin base. Narrow, dark ventral stripe from first anal-fin ray to ventral caudal-fin procurrent rays. Usually, only base of first pectoral-fin ray, and rarely others, pigmented. Dorsal, anal and posterior half of caudal-fin rays densely pigmented.

Sexual dimorphism. Anal-fin base slightly concave in females, and nearly straight in males. Number of scales between pelvic-fin insertions in mature males 5(7) or 6(4), in females 1(6) or 2(4). Scales between mesial pelvic-fin rays larger with more radii than other body scales (except for pouch scale) in mature males, and equal in size in females and juveniles. Number of scales between mesial pelvic-fin rays 2(2) or 3(9) in mature males (a single male with one large scale, almost as large as the pouch scale), and 1(10) in females. Pouch scale somewhat teardrop shaped, similar to that of X. polyancistrus ( Weitzman 1987: fig. 3) but with numerous, loosely positioned radii extending over posterior, posterodorsal, and posteroventral margins, being more numerous on latter portion.

Tip of pectoral fin at vertical through 9 th (11) or 11 th (1) scale of lateral line longitudinal series in mature males, whereas in females and juveniles, tip of pectoral fin located at vertical through 11 th (7) scale. Pelvic fin hyaline in females and juvenile specimens inserted at vertical through 10 th (9) scale of lateral line longitudinal series, with vii(16) rays. In mature males, pelvic fin pigmented from first to fourth, or sometimes fifth ray, inserted at vertical through 5 th (11) or 7 th (l) scale of lateral line longitudinal series; pelvic-fin rays i,6(1), ii,5*(11) or ii,6(5). Mature males with two unpaired antrorse hooks per segment on ventral margin of unbranched and branched pelvic-fin rays; hooks increasing in size until middle of hooked portion, then decreasing distally; hooks on first unbranched ray larger than on branched ones. Anterior tip of pelvic bone located anterior to vertical through pectoral-fin rays insertion (5), posterior tip of pelvic bone between 2 nd and 3 rd (5) ribs in mature males. In female and juvenile specimens, anterior tip of pelvic bone between 1 st and 2 nd (6) ribs, posterior tip of pelvic bone at 3 rd (2) or between 3 rd and 4 th (4) ribs. Pelvic -fin of mature males significantly longer than in females (32.2-38.9% SL vs. 9.1-13.3% SL p<0.001; Fig. 6 ). Distance between snout to pelvic-fin insertion between male and female or juvenile specimens (28.0-36.0% SL vs. 33.9-43.2% SL; Fig. 7 ) not significantly different.

Anterior anal-fin lobe formed by 3 rd unbranched ray and anteriormost four branched rays ( Fig. 4a ), longer in mature males than in females. Lamellar process of pterygiophores well developed in 1 st proximal radial, gradually increasing in size from 7 th to 16 th or 17 th proximal radials but poorly developed or, absent from 2 nd to 6 th pterygiophores ( Fig. 4b ). Bilateral, antrorse anal hooks located from 3 rd unbranched ray to 8 th branched rays, and strongly recurved hooks on branched rays 9 th- 12 th; usually one pair on each segment. Anal hooks roughly equal in size, but larger on posteriormost rays. Caudal-fin musculature of mature males same as that described for X. macropus (Weitzman & Fink, 1985: 77, 81-83, and fig. 11). Caudal-fin rays with bilateral antrorse hooks, usually one pair per lepidotrichia segment; approximately equal in size on most rays but lager on unbranched rays ( Fig. 3a ). In mature males, set of lamellar processes present on eighth principal caudal-fin ray of lower lobe composed by ventral, paired lamellar expansions on 3 rd to 5 th lepidotrichia segments, and an unpaired lamellar expansion from 4 th to 5 th lepidotrichia segments ( Fig. 3b ).

Distribution. Xenurobrycon varii is known from tributary streams of rio Tapajós and rio Jamanxim ( Fig. 8 ).

Etymology. This species is named in honor of Richard P. Vari, an esteemed person and ichthyologist, for his contributions to the systematics of fishes and his continuous support and aid to the authors.

Conservation status. Considering that present relevant threats to the species were not detected in its distribution area, Xenurobrycon varii could be classified as Least Concern (LC), according to the International Union for Conservation of Nature (IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2014). On the other hand, at least five major hydroelectric power plants denominated Complexo Tapajós (São Luiz do Tapajós, Jatobá, Cachoeira dos Patos, Cachoeira do Caí and Jamanxim) are expected to be built in the occurrence area of the species by the Brazilian government, causing highly plausible impacts to the population of Xenurobrycon varii , leading to a revaluation of the conservation status of the species, along with others, in the medium term.

Figures

Fig. 3. Xenurobrycon varii, MPEG 26591, male, 15.0 mm SL, left side of caudal-fin rays (pouch-scale removed): (a) bilateral, antrorse hooks, usually one pair per lepidotrichium segment (rectangle indicates magnified area represented in b); (b) set of lamellar processes on eighth principal caudal-fin ray of lower lobe, dashed lines represent the delimitation of left elements of paired ventral processes and dorsal unpaired process along ray segments 3 to 5 and 4 to 5, respectively. Scale bars = 1 mm and 0.25 mm respectively.

Fig. 4. Xenurobrycon varii, anal-fin rays:(a) left side, MPEG 26591, male, 15.0 mm SL, with bilateral, antrorse hooks; (b) right side (inverted), MPEG 26592, male, 13.5 mm SL, with well-developed lamellar process on pterygiophores. Scale bars = 1 mm and 0.25 mm respectively.

Fig. 5. Xenurobrycon varii, MPEG 25239, 13.4 mm SL, left side of maxilla and premaxilla and right side (inverted) of dentary, Scale bars = 0.2 mm.

Fig. 6. ANCOVA plot showing the difference between pelvic-fin length of mature males and females of Xenurobrycon varii.

Fig. 7. ANCOVA plot showing relation between snout to pelvic-fin length and SL of mature males and females of Xerunobrycon varii.

Fig. 8. Map of portion of rio Tapajós basin, and adjoining areas, showing collecting sites (dark circles) and the type locality (white circle) of Xenurobrycon varii.