Priocharax conwayi, Mattox & Lima & Britz & Souza & Oliveira, 2024

Mattox, George M. T., Lima, Flávio C. T., Britz, Ralf, Souza, Camila S. & Oliveira, Claudio, 2024, Two new miniature species of the fish genus Priocharax from the Rio Tapajós and Amazonas drainages, Pará, Brazil (Teleostei: Characiformes: Characidae), Vertebrate Zoology 74, pp. 533-550 : 533-550

Priocharax conwayi sp. nov.

Figures 1 , 2 , 3

Holotype.

MZUSP 129745 , 12.2 mm SL, Brazil, Pará State, Santarém municipality, Rio Mentaí, in the vicinity of settlement Boca do Mentaí, affluent of Rio Arapiuns, Rio Tapajós drainage , 02 ° 37 ’ 52.51 ” S 55 ° 34 ’ 40.98 ” W, 04 Nov 2021, G. M. T. Mattox, F. C. T. Lima, M. Lima, E. Cerdeira.

Paratypes.

All from Brazil, Pará State, Santarém municipality, Rio Tapajós basin : LBP 31741 (5, not measured), INPA 60217 (20, 8.4–14.2 mm SL), MPEG 39636 (20, 10.8–12.9 mm SL), MZUSP 129746 (190, 10.8–19.0 mm SL; 18 c & s, 10.3–12.3 mm SL), UFOPA-I 1367 (20, 9.2–12.3 mm SL) and ZUEC 17853 (30, 9.6–12.8 mm SL), collected with holotype ; MCP 55310 (3, 11.4–11.9 mm SL); UF 249762 (2, 11.0– 11.6 mm SL); ZUEC 11648 (10, 11.2–17.5 mm SL), same locality as holotype, 21–24 Nov 2015, F. C. T Lima, E. Cerdeira, B. B. Calegari ; LBP 31740 (3, not measured) and MZUSP 129747 (47, 11.1–14.5 mm SL), Igarapé do Henrique, Rio Maró, affluent of Rio Arapiuns, Rio Tapajós drainage , 02 ° 41 ’ 9.30 ” S 55 ° 40 ’ 32.97 ” W, 05 Nov 2021, G. M. T. Mattox, F. C. T. Lima, M. Lima, E. Cerdeira ; ZUEC 8774 (1, 11.1 mm SL), same locality as previous, 19 Nov 2013, F. C. T. Lima, W. G. R. Crampton, J. S. Ready, E. Cerdeira .

Diagnosis.

Priocharax conwayi sp. nov. is distinguished from all congeners except P. nanus and P. toledopizae by the presence of the claustrum (vs. absence). Priocharax conwayi sp. nov. is distinguished from all congeners except P. ariel by the presence of three infraorbitals, Ios 1 + 2 + 3 (vs. absence of infraorbitals in P. nanus , P. pygmaeus and P. varii ; presence of a single infraorbital, Io 2, in P. britzi and P. marupiara ; presence of two infraorbitals, Ios 1 + 2, in P. marupiara , P. phasma sp. nov. and P. toledopizae ). Priocharax conwayi sp. nov. can be distinguished from P. nanus and P. varii by fewer premaxillary teeth (14–20 vs. 23–29), from P. ariel , P. nanus and P. varii by fewer maxillary teeth (24–29 vs. 32–45), and from P. ariel and P. varii by fewer dentary teeth (24–34 vs. 35–46). The presence of a single postcleithrum distinguishes P. conwayi sp. nov. from P. britzi , P. marupiara , P. nanus , P. toledopizae , and P. varii (vs. two), and from P. pygmaeus (vs. absence). Priocharax conwayi sp. nov. can be further distinguished from P. nanus and P. varii by five branched pelvic-fin rays (vs. six), and from P. varii by the absence of an adipose fin (vs. presence). Priocharax conwayi sp. nov. is further distinguished from P. phasma sp. nov. by the shorter anal-fin base (25–31 % SL vs. 32–38 % SL) and longer caudal peduncle (18–24 % SL vs. 13–19 % SL).

Description.

For overall appearance, see Figure 1 . Morphometric data are presented in Table 2 . Body laterally compressed and elongated, greatest depth at vertical through pelvic-fin in small specimens, at vertical through dorsal-fin origin in larger specimens. Dorsal-fin origin approximately at midbody, at vertical through vent and slightly anterior to anal-fin origin. Pectoral-fin bud at vertical through anterior portion of pseudotympanum. Pelvic-fin origin slightly posterior to vertical at midway between posterior margin of opercle and anal-fin origin. Dorsal profile of head and body slightly convex from tip of snout to dorsal-fin origin. Dorsal profile of body along dorsal-fin base nearly straight, gently sloping posteroventrally; slope less conspicuous from latter point to caudal peduncle. Dorsal profile of caudal peduncle straight to base of dorsal procurrent rays. Ventral profile of head and body slightly convex from symphysis of lower jaw to vertical through pectoral-fin origin; straight to slightly convex from latter point to anal-fin origin. Ventral profile of body slightly concave and posterodorsally rising along anal-fin base, slightly concave from end of anal-fin base to origin of ventral procurrent rays. Caudal peduncle short and relatively robust. Pseudotympanum large, located anterior to rib of fifth vertebra.

Snout round in lateral view. Eye diameter about one-third of head length. Antorbital and infraorbitals 1, 2 and 3 present (n = 8) (Fig. 2 A ). Infraorbitals 4 to 6 and supraorbital absent (n = 8). Mouth terminal. Tip of maxilla elongate, posterior border reaching vertical through midway between middle and posterior border of eye, but closer to middle of eye in largest males. Premaxillary teeth in single series, premaxilla with 15 (1), 18 (4), or 19 (3) teeth. Maxilla with 24 (1), 26 (4), 27 (2), or 28 (1) teeth. Dentary with 27 (2), 28 (1), 29 (2), or 30 (3) teeth. Dentary teeth in single series, with few anterior teeth slightly displaced from series anteriorly. A conspicuous, elongate foramen at the anterior portion of the dentary. All jaw teeth small, conical and curved lingually to a moderate extent (Fig. 2 B ).

Dorsal-fin rays ii, 8 (7) or ii, 9 * (118). Endoskeletal part of pectoral fin and some thin exoskeletal bones of the pectoral girdle showing larval structure (Fig. 2 C ). Cartilaginous pectoral-radial plate with incomplete longitudinal middle fissure leaving upper and lower halves connected at base and tip; base articulating with vertically elongated scapulocoracoid cartilage and round distal margin with larval-like pectoral-fin fold supported solely by actinotrichia. Pectoral-fin rays absent. All bones of endoskeletal pectoral girdle absent, exoskeletal part with posttemporal, supracleithrum, cleithrum and one postcleithrum. Cleithrum with posteriorly directed, curved process immediately below ventral tip of supracleithrum. Pelvic-fin rays i, 5 * (125). Posterior tip of pelvic fin on vertical through vent in females and extending further posterior slightly beyond anal-fin origin in males. Anal-fin rays ii, 16 (1), ii, 18 (1), ii, 19 (19), ii, 20 (36), ii, 21 * (47), ii, 22 (17), or ii, 23 (1). Anal-fin margin concave with anterior lobe formed by elongated fin rays and posterior section of short rays. Principal caudal-fin rays 9, 9 (1), 10, 8 (1), 10, 9 * (115) or 10, 10 (1), dorsal procurrent rays 6 (1), 7 (2), or 8 (5), ventral procurrent rays 5 (1), 6 (3), or 7 (4). Caudal fin forked. Adipose fin absent.

Squamation present in almost all specimens, but scales highly deciduous and easily lost during handling. Scales cycloid, very thin, with no obvious circuli or radii. Scales in midlateral row 19 (5), 20 (8), 21 (19), 22 (29), 23 * (21), 24 (20), 25 (4), 26 (5), 27 (2), or 28 (5); no canal-bearing lateral line scales. Scale rows between dorsal-fin origin and pelvic-fin origin 8 (2) or 9 * (8). Scale rows around caudal peduncle 10 * (10). Predorsal scales typically absent but occasionally one or two scales present immediately anterior to dorsal fin. Caudal-fin squamation restricted to base of caudal-fin rays, no scales on caudal-fin lobes.

Total vertebrae 32 (8) with 13 (1), or 14 (7) abdominal vertebrae and 18 (7), or 19 (1) caudal vertebrae. Total number of gill-rakers on first branchial arch 11 (1), 12 (4), 13 (2) or 14 (1), with 3 (3) or 4 (5) gill-rakers on upper limb, and 8 (3), 9 (4), or 10 (1) gill-rakers on lower limb. Weberian apparatus well-developed, all components ossified including claustrum (Fig. 2 D ). Large gap between neural arches 3 and 4, with gap partially covered by dorsally projecting pointed process from vertebra 3. Inner arm of os suspensorium large, projecting forward to vertical through middle of second centrum. Supraneurals 5 (5) or 6 (3).

Color in alcohol.

Overall body color pale yellow (Fig. 1 B – D ). Melanophores scattered on dorsal surface of head in region of brain. Horizontal line of two melanophores from tip of snout to anterior margin of orbital cavity in some specimens. A conspicuous melanophore approximately at articulation between premaxilla and maxilla, and another conspicuous melanophore ventral to that, on dentary. A line of 3-4 melanophores along posteroventral margin of dentary, with patch of melanophores concentrated on posterior margin of lower jaw. A few specimens with inconspicuous line of three deep melanophores radiating horizontally from posterior margin of orbital cavity. Deep melanophores along ventral margin of neurocranium. Thin line of melanophores along posteroventral margin of orbital cavity. Dorsal portion of eye black, with melanophores fading ventrally towards middle of eye. Overall coloration of eye silver with guanine. Deep vertical lines of 2-3 melanophores on anterior portion of heart chamber and halfway between heart chamber and pelvic-fin base. Line of superficial melanophores along pelvic-fin base, a single melanophore on ventral surface of body at vertical through middle of pelvic fin, and a deep inconspicuous vertical line of melanophores from anus along posterior portion of abdominal cavity. These vertical lines give a striped aspect to ventral portion of body along abdominal cavity. Thick patch of melanophores along dorsal surface of swim bladder, more visible through pseudotympanum. Irregular thin line of melanophores along dorsal-fin base. A few specimens with irregular line of melanophores along dorsal profile of body. Thin line of scattered melanophores along entire anal-fin base, and another thicker line of melanophores along ventral margin of hypaxial myomeres starting at vertical through 8-9 th anal-fin ray, approaching thin line of anal-fin base posteriorly. Both lines continuing posteriorly to caudal-fin ventral procurrent rays. Two or three isolated melanophores along midlateral surface of caudal peduncle. Scattered melanophores on lateral surface of hypural plate. Fins mostly hyaline, with small dark patch on first rays of dorsal- and anal-fin bases. Dorsal, anal and caudal fins with scattered melanophores along rays.

Color in life.

Body mostly translucent, with patterns of melanophores as described in alcohol specimens (Fig. 1 A ). Xanthophores scattered on dorsal surface of head and snout. Anterior tip of dentary with few xanthophores. Scattered xanthophores on dorsal midline of body anterior to dorsal fin and dorsal surface of swim bladder. Line of conspicuous superficial xanthophores extending from anterior portion of swim bladder to tip of caudal peduncle. Xanthophores along dorsal surface of vertebral column. Line of xanthophores along dorsal-fin base and small patch of xanthophores on base of anterior two or three dorsal-fin rays. Few xanthophores along anterior portion of anal-fin base approximately at level of first five anal-fin rays. Xanthophores along some of longest principal caudal-fin rays.

Sexual dimorphism.

Hooks present on anal- and pelvic-fin rays of mature males as small as 11.1 mm SL and 12.4 mm SL, respectively (Fig. 3 A, B ). Hooks better developed on anal fin. Hooks on anal fin present in longest unbranched and subsequent branched rays up to seventh ray, one pair of hooks on posterior edge of six to nine distal segments of rays. Approximately six to ten small hooks on medial margin of four lateralmost branched pelvic-fin rays in most mature males (n = 3). Two specimens (11.1–13.5 mm SL) with a horizontal slit along the dorsal portion of the pelvic-fin musculature (Fig. 3 A ). Overall size of pelvic girdle in mature males larger than that of females, pelvic bone restricted posteriorly to level of rib of sixth vertebra in females, but reaching further anteriorly (e. g., halfway between ribs of fifth and sixth vertebra, or rib of fifth vertebra) in mature males. Basipterygium of males better ossified, more robust, and closer to contralateral part than in females. General color pattern more pronounced in males than in females.

Distribution.

Priocharax conwayi sp. nov. is known from two localities in the upper Rio Arapiuns, Rio Tapajós system, Santarém municipality, Pará State, Brazil: rios Mentaí and Maró (Fig. 4 ).

Ecological notes.

Priocharax conwayi sp. nov. occurs in black water systems and was collected in two slightly different habitats, a shallow riverine area at the margin of the flooded forest presenting dense aquatic vegetation and a small, slow-flowing forest stream also presenting dense aquatic vegetation (Fig. 5 A, B ). Individuals were collected along the margins where riparian vegetation was still present. At the type locality, Priocharax conwayi sp. nov. was collected with the small scale pike characin Acestrorhynchus minimus Menezes, 1969 , the characin tetras Charax condei (Géry & Knöppel, 1976) , Microschemobrycon melanotus (Eigenmann, 1912) , and Tyttobrycon xeruini Géry, 1973 , the tetras Hemigrammus analis Durbin, 1909 , Hemigrammus levis Durbin, 1908 , Hemigrammus stictus (Durbin, 1909) , Hyphessobrycon diancistrus Weitzman, 1977 , the toothless characin Curimatopsis cryptica Vari, 1982 , a juvenile of the wolf-fish Hoplias sp. , the pencil fishes Nannostomus digrammus (Fowler, 1913) , Nannostomus unifasciatus Steindachner, 1876 , unidentified larvae of Characiformes , larvae and juveniles of the pacu Metynnis sp. , the checkerboard cichlid Dicrossus maculatus Steindachner, 1875 , the flag cichlid Mesonauta insignis (Heckel, 1840) , the eleotrid Microphilypnus ternetzi Myers, 1927 , the guppy Poecilia scalpridens (Garman, 1895) , and the lampeye Fluviphylax simplex Costa, 1996.

Etymology.

Priocharax conwayi sp. nov. honours Dr. Kevin W. Conway, esteemed friend and notable ichthyologist. Dr. Conway has greatly contributed to our knowledge of miniature fish taxonomy and morphology. A noun in the genitive case.

Figures

Figure 1. Priocharax conwayi sp. nov. A Live paratype, MZUSP 129746, female, not measured, Brazil, Pará State, Santarém municipality: Rio Mentaí, in vicinity of settlement Boca do Mentaí, tributary of Rio Arapiuns, Rio Tapajós drainage. B Paratype, MZUSP 129746, male, 10.7 mm SL, collected with holotype. C Holotype, MZUSP 129745, female, 12.2 mm SL, Brazil, Pará State, Santarém municipality: Rio Mentaí, in vicinity of settlement Boca do Mentaí, tributary of Rio Arapiuns, Rio Tapajós drainage. D Paratype, same specimen as (B).

Figure 2. Priocharax conwayi sp. nov., paratype, MZUSP 129746, male, 12.1 mm SL, c & s. A Dorsolateral view of head showing infraorbital bones. B Jaws in lateral view. C Right pectoral girdle in lateral view, image flipped. D Weberian apparatus in lateral view. E Detail of claustrum. Abbreviations: Ana, anguloarticular; Ant, antorbital; Cl, cleithrum; Cla, claustrum; Cm, coronomeckelian; De, dentary; Ect, ectopterygoid; Exoc, exoccipital; Fr, frontal; Int, intercalarium; Io 1–3, infraorbitals 1–3; LEt, lateral ethmoid; Mx, maxilla; NA 3–4, neural arches 3–4; PecRdC, pectoral-fin radial cartilage; Pcl, postcleithrum; Pmx, premaxilla; Pt, posttemporal; OsS, os suspensorium; Qua, quadrate; Ra, retroarticular; Sc, scaphium; ScCoC, scapulocoracoid cartilage; Sn 3, supraneural 3; Suc, supracleithrum; Tr, tripus. Scale bar: (A) 2 mm, (B) 0.5 mm, (C) 1 mm, (D) 0.5 mm, (E) 0.25 mm.

Figure 3. A Priocharax conwayi sp. nov., paratype, male, ZUEC 11648, 13.5 mm SL, lateral view of anal fin showing the bony hooks. B Priocharax conwayi sp. nov., paratype, female, MZUSP 129746, 11.1 mm SL, c & s, lateral view of the ventral portion of the body showing rib of fifth vertebra (red arrow), anterior tip of basipterygium (black arrow) and anal-fin rays without hooks. Anal fin slightly damaged and specimens with alizarin red faded. C Priocharax phasma sp. nov., paratype, male, MZUSP 129750, 12.8 mm SL, lateral view of anal fin showing the bony hooks. D Priocharax phasma sp. nov., paratype, female, MZUSP 129749, c & s, lateral view of the ventral portion of the body showing rib of fifth vertebra (red arrow), anterior tip of basipterygium (black arrow) and anal-fin rays without hooks. E Priocharax phasma sp. nov., same specimen as (C) showing longitudinal slit along the pelvic girdle musculature (black arrows).

Figure 4. Map of South America showing details of lower Rio Tapajós and tributary Rio Arapiuns, and Rio Amazonas close to mouth of Rio Tapajós, in vicinity of Santarém municipality, Pará State, Brazil, with records of Priocharax conwayi sp. nov. (losangle and triangle) and Priocharax phasma sp. nov. (circle and star). Triangle and star represent type localities.

Figure 5. Type localities of Priocharax conwayi sp. nov. (A, B) and P. phasma sp. nov. (C). (A) General view of type locality: Rio Mentaí, in vicinity of settlement Boca do Mentaí, tributary of Rio Arapiuns (B) Detail of submerged macrophytes associated with Priocharax specimens in (A). (C) General view of type locality: Lago Santana, Ilha de Marimarituba, Rio Amazonas near the mouth of Rio Tapajós. Both localities in Santarém municipality, Pará State, Brazil.