Priocharax phasma Mattox, Lima, Britz, Souza & Oliveira, 2024, sp. nov.
Creators: name: Mattox, George M. T.
name: Lima, Flávio C. T.
name: Britz, Ralf
name: Souza, Camila S.
name: Oliveira, Claudio
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Characiformes
Characidae
Priocharax
Priocharax phasma

description: Priocharax phasma sp. nov.
Figures 3, 6, 7
Holotype.
MZUSP 129748, 10.2 mm SL, Brazil, Pará State, Santarém municipality, Lago Santana, Ilha de Marimarituba, Rio Amazonas near Rio Tapajós mouth, 02 ° 11 ’ 12.31 ” S 55 ° 02 ’ 12.00 ” W, 07 Nov 2021, G. M. T. Mattox, F. C. T. Lima, M. Lima, E. Cerdeira.
Paratypes.
All from Brazil, Pará State, Santarém municipality, Rio Amazonas basin: LBP 31742 (10, 9.2–11.0 mm SL), INPA 60218 (20, 9.5–11.0 mm SL), MPEG 39637 (20, 9.2–10.7 mm SL), MZUSP 129749 (348, 9.5–13.8 mm SL; 28 c & s, 10.1–11.2 mm SL), UFOPA-I 1368 (20, 9.3–12.9 mm SL) and ZUEC 17854 (30, 8.7–12.0 mm SL), collected with holotype; LBP 31743 (3, 9.7–12.1 mm SL) and MZUSP 129750 (5, 9.9–12.8 mm SL), Lago Pajaú, Ilha Nazareth, Rio Amazonas near mouth of Rio Tapajós, 02 ° 11 ’ 28.53 ” S 54 ° 51 ’ 27.93 ” W, 06 Nov 2021, G. M. T. Mattox, F. C. T. Lima, M. Lima, E. Cerdeira; ZUEC 8998 (2, 9.3–10.3 mm SL), Lago Pajaú (or Tamoatá), Ilha Nazareth, Rio Amazonas near mouth of Rio Tapajós, 2 ° 11 ’ 29 ” S 54 ° 51 ’ 28 ” W, 21 Sep 2013, F. C. T. Lima, J. S. Ready, W. G. R. Crampton, E. Cerdeira; MCP 55309 (2, 10.4–12.2 mm SL); UF 249763 (2, 10.1–10.3 mm SL); ZUEC 9017 (5, 10.1–12.3 mm SL), same locality as holotype, 21 Sep 2013, F. C. T. Lima, J. S. Ready, W. G. R. Crampton, E. Cerdeira.
Diagnosis.
Priocharax phasma sp. nov. is distinguished from all congeners by the complete lack of pigmentation on the body (vs. presence of at least some chromatophores), and by fewer maxillary teeth in slightly irregular series (13–21 vs. 21–45). Priocharax phasma sp. nov. is distinguished from all congeners except P. conwayi sp. nov. by fewer dentary teeth (18–26 vs. 26–55). It is distinguished from all congeners except Priocharax ariel and P. conwayi sp. nov. by the presence of a single postcleithrum (vs. two in most congeners and absence in P. pygmaeus). The presence of two infraorbitals, Ios 1 + 2, distinguishes Priocharax phasma sp. nov. from most congeners except P. marupiara and P. toledopizae (vs. three infraorbitals, Ios 1 + 2 + 3 in P. ariel and P. conwayi sp. nov.; one infraorbital, Io 2, in P. britzi; and absence of infraorbitals in P. nanus, P. pygmaeus and P. varii). Priocharax phasma sp. nov. has more branched anal-fin rays than P. ariel (21–26 vs. 16–21), and fewer branched pelvic-fin rays than P. nanus and P. varii (five vs. six). P. phasma sp. nov. is further distinguished from P. conwayi sp. nov., P. nanus and P. toledopizae by the absence of the claustrum (vs. presence), and from P. varii by the absence of the adipose fin (vs. presence). It also has a longer anal-fin base (32–38 vs. 25–31) and a shorter caudal peduncle (13–19 vs. 18–23) than Priocharax conwayi sp. nov.
Description.
For overall appearance, see Figure 6. Morphometric data are presented in Table 3. Body laterally compressed and elongated, greatest depth at vertical through dorsal-fin origin. Dorsal-fin origin approximately at midbody, at vertical through anal-fin origin. Pectoral-fin bud at vertical through anterior portion of pseudotympanum. Pelvic-fin origin approximately 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, and straight from latter point to base of ventral procurrent rays. Caudal peduncle narrow and elongate. Pseudotympanum located anterior to the rib of the fifth vertebra.
Snout rounded in lateral view. Eye diameter about one-third of head length. Antorbital and infraorbitals 1 and 2 present, infraorbitals 3–6 and supraorbital absent (n = 18) (Fig. 7 A). Mouth terminal. Tip of maxilla elongate, posterior border almost reaching vertical through posterior border of eye. Premaxillary teeth in single series, with 15 (3), 16 (2), 17 (5), 18 (3), 20 (1), 22 (1), or 23 (1) teeth. Maxilla with 12 (1), 13 (4), 15 (1), 16 (1), 17 (2), 18 (2), 19 (1), or 20 (3) teeth. Dentary with 17 (1), 18 (2), 19 (3), 20 (4), 21 (1), 22 (3), 23 (1), 24 (2) or 25 (1) teeth. Dentary teeth in single series, with few anterior teeth slightly displaced from series anteriorly. Conspicuous elongate foramen at anterior portion of dentary. All jaw teeth small, conical and curved lingually to moderate extent (Fig. 7 B).
Dorsal-fin rays ii, 8 (2), ii, 9 * (72), or ii, 10 (1). Endoskeletal part of pectoral fin and some thin exoskeletal bones of the pectoral girdle showing larval structure (Fig. 7 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, 4 (1) or i, 5 * (77). Posterior tip of pelvic fin on vertical through vent in females and extending further posterior to anal-fin origin in males. Anal-fin rays ii, 21 (5), ii, 22 (8), ii, 23 * (16), ii, 24 (20), ii, 25 (16), ii, 26 (6), or ii, 27 (2). Anal-fin margin concave with anterior lobe formed by elongated fin rays and posterior section of short rays. Principal caudal-fin rays 10, 9 * (69), dorsal procurrent rays 8 (4), 9 (10), or 10 (2), ventral procurrent rays 6 (7), 7 (10), or 8 (1). 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 20 (1), 21 (8), 22 (6), 23 (14), 24 * (14), 25 (14), or 26 (5); no canal-bearing lateral line scales. Scale rows between dorsal-fin origin and pelvic-fin origin 7 (1) or 8 * (9). Scale rows around caudal peduncle 8 (2) or 10 * (8). Predorsal scales typically absent, occasionally with one or two scales immediately anterior to the dorsal fin. Caudal-fin squamation restricted to base of caudal-fin rays, no scales on caudal-fin lobes.
Total vertebrae 32 (2), 33 (15), or 34 (2) with 14 (12), or 15 (6) abdominal vertebrae and 17 (1), 18 (5), 19 (11), or 20 (1) caudal vertebrae. Total number of gill-rakers on first branchial arch 8 (2), 9 (3), 10 (4), 11 (5), 12 (3), or 13 (1), 2 (13), or 3 (5) gill-rakers on upper limb, and 6 (2), 7 (5), 8 (2), 9 (7), or 10 (2) gill-rakers on lower limb. Weberian apparatus well-developed, all components ossified except for claustrum, which is absent (Fig. 7 D). Large gap between neural arches 3 and 4, 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 (7), 6 (5), 7 (5), or 8 (1).
Color in alcohol.
Overall body color pale yellow (Fig. 6 B – D). Melanophores absent from most parts of body, except for thin inconspicuous superficial line along ventral portion of hypaxial myomeres starting at vertical through 10-11 th anal-fin ray and extending to last anal-fin ray. Scattered melanophores forming inconspicuous line along base of caudal-fin rays. Eye silvery with guanine, with thin line of melanophores along dorsal margin.
Color in life.
Body mostly translucent, with patterns of melanophores as described in alcohol specimens (Fig. 6 A). Thin line of melanophores along anal-fin base and ventral profile of caudal peduncle up to level of ventral procurrent caudal rays. Patch of xanthophores on dorsal surface of head and along vertebral column. All fins hyaline.
Sexual dimorphism.
Hooks present either on anal-fin (10.7–12.3 mm SL, n = 7) or on both anal- and pelvic-fin rays (10.7–13.4 mm SL, n = 11) of mature males (Fig. 3 C, D). Hooks better developed on anal fin. Anal-fin hooks present on longest unbranched ray and anterior three branched rays, one pair of hooks at posterior edge of distal four or five segments of branched rays, and two pairs in middle segments on longest unbranched ray. One or two poorly developed hooks on medial margin of first and second branched pelvic-fin rays in most mature males (11 out of 18 males). One specimen (12.8 mm SL) with a horizontal slit along the dorsal portion of the pelvic-fin musculature (Fig. 3 E). This specimen has the ventral profile of body along the anal fin sinuous. 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 at level of rib of fifth vertebra) in mature males.
Distribution.
Priocharax phasma sp. nov. is known from floodplain lakes on two islands, Ilha Marimarituba and Ilha Nazareth, in the Rio Amazonas slightly upstream from the Rio Tapajós mouth, Santarém municipality, Pará State, Brazil (Figs 4, 5).
Ecological notes.
Priocharax phasma sp. nov. was sampled among marginal vegetation (presumably Echinochloa sp. or Paspalum sp. grasses) in both lakes, at depths approximately between 0.5–1 m (Fig. 5). Other fish species sampled with Priocharax phasma sp. nov. at the type locality were a larva of the pike characin Acestrorhynchus sp., the characin tetras Phenacogaster sp., Roeboides descalvadensis Fowler, 1932, the tetras Aphyocharax nattereri (Steindachner, 1882), Hemigrammus hyanuary Durbin, 1918, Hemigrammus sp., Hyphessobrycon sp., Prionobrama filigera (Cope, 1870), Serrapinnus micropterus (Eigenmann, 1907), the hatchet characin Triportheus albus Cope, 1872, the armored catfish Farlowella amazona (Günther, 1864), the flag cichlid Mesonauta insignis (Heckel, 1840), juveniles of the demon eartheater Satanoperca sp, and the eleotrid Microphilypnus ternetzi Myers, 1927.
Etymology.
The name phasma is derived from the Greek word φάσμα which means ghost. It alludes to the almost completely transparent appearance of the new species, resembling a ghost. A noun in apposition.
Molecular data analysis
The molecular dataset included 50 sequences with 526 bp and 230 variable sites (43.7 %). The nucleotide frequencies were 23.9 % adenine, 16.8 % guanine, 33 % thymine, and 26.2 % cytosine. DAMBE indicated no saturation for either transitions or transversions in both asymmetrical (Iss. cAsym) and symmetrical (Iss. cSym) topologies. The maximum likelihood (ML) tree showed high bootstrap values supporting each of the analyzed species (Fig. 8). The best partition proposed by ASAP recognized 9 species (asap-score: 2.00) supporting Priocharax conwayi sp. nov. and Priocharax phasma sp. nov. as new species. ML solution of the bPTP analysis recovered identical results (Figs 8, S 1). The overall mean of genetic distances (K 2 P) among Priocharax species was 21.3 %. Intraspecific genetic distances ranged from 0 % within Priocharax pygmaeus and P. marupiara to 0.2 % within P. ariel, P. conwayi sp. nov., P. phasma sp. nov. and P. varii. The values of interspecific distances ranged from 8.8 % between Priocharax pygmaeus and P. toledopizae to 31.8 % between P. pygmaeus and P. ariel. The genetic distance between Priocharax conwayi sp. nov. and P. phasma sp. nov. was 26.4 % (Table 4).
description: Published as part of 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), pp. 533-550 in Vertebrate Zoology 74 on pages 533-550, DOI: 10.3897/vz.74.e130038