Poecilocharax rhizophilus, Ohara & Pastana & Camelier, 2023

Ohara, Willian M., Pastana, Murilo & Camelier, Priscila, 2023, The monophyly of Crenuchinae and description of two new species of Poecilocharax (Teleostei: Crenuchidae) based on phenotypic and genotypic evidence, Zoological Journal of the Linnean Society 197 (2), pp. 442-473 : 455-460

POECILOCHARAX RHIZOPHILUS SP. NOV.

( FIGS 12–14 ; TABLE 3 )

Zoobank registration: urn: lsid: zoobank. org:act: 1B74686B-BA11-4F5F-829F-28ECD9A13C1E.

Holotype: MZUSP 121652 , male, 20.3 mm SL, BRAZIL, Amazonas State , Apuí , Igarapé Mutum , tributary of the Rio Juma , Rio Aripuanã drainage, Rio Madeira Basin, 7º14′58′′S 59º58′40′′W, 123 m a.s.l., 10 October 2016, O. Oyakawa, W. Ohara, M. Pastana and T. Teixeira (collectors).

Paratypes: BRAZIL, Amazonas State, Apuí. MZUSP 121651 (30, 15.9–23.4 mm SL; 3 C&S, 14.9–17.9 mm SL; 4 MOL, 16.7–19.5 mm SL) ; INPA 59405 (5, 16.6–17.5 mm SL) ; MNRJ 51748 (5, 16.1–19.1 mm SL), same data as the holotype . MZUSP 117653 (1, 16.2 mm SL), Rio Madeira Basin , Rio Aripuanã drainage, Rio Juma upstream from Paredão waterfall, 7º02′58′′S 60º03′04′′W, 23 June 2015, W. M. Ohara and V. Abrahão (collectors) .

Diagnosis: Poecilocharax rhizophilus can be promptly distinguished from its congeners, except P. weitzmani , by having the anterior and posterior nares separated from each other by a distance equal to or greater than anterior nostril diameter (see Géry, 1965: fig. 11; vs. anterior and posterior nares separated only by a narrow skin fold); and by the absence of a nasal flap (vs. presence). The new species can be distinguished from P. weitzmani by the absence of a dark suborbital bar (vs. presence); absence of maxillary teeth (vs. presence); presence of a small unbranched ray preceding the two long unbranched anal-fin rays (vs. absence); presence of a dark humeral spot (vs. absence); absence of dark pigmentation on the median margin of the branchiostegal membrane in dimorphic males (vs. presence) and by its overall yellowish colour in life (vs. overall colour in life reddish).

Description: Morphometric data presented in Table 3 . Miniature species, largest specimen analysed reaching 23.3 mm SL ( Fig. 12 ). Body moderately compressed and elongated. Greatest body depth approximately at vertical through tip of pectoral fin. Dorsal profile convex between tip of snout and base of last dorsalfin ray; straight or slightly concave between that point to origin of anteriormost dorsal procurrent caudal-fin ray. Ventral profile of head convex; ventral profile of the body straight or slightly convex from posterior portion of the head to anal-fin origin; slightly convex along anal-fin base; straight or slightly concave between terminus of anal fin to origin of anteriormost ventral procurrent caudal-fin ray. Body elliptical in cross-section at pectoral-fin origin, broader ventrally, gradually becoming more compressed toward caudal-fin base.

Mouth small, terminal, jaws vertically aligned anteriorly. Snout shorter than eye diameter, gently rounded. Maxilla short, reaching level of anterior margin of orbit. Orbital margin free. Cheek narrow, less than half of eye diameter. Anterior and posterior nares conspicuously separated from each other; lacking a skin flap. Anterior naris circular, posterior naris crescent-shaped. Dorsal profile of head concave, concavity extending anteriorly from mesethmoid to midlength of frontal bones portion, allocating a frontal organ. Each frontal containing one relatively large foramen for passage of the trigeminal branch ophthalmicus superficialis that innervates the organ. Supraorbital absent. Antorbital positioned dorso-anteriorly to infraorbital 1; infraorbitals 2, 3 and 4 present (3); infraorbitals 5 and 6 absent (3). Pseudotympanum present, underneath third to fifth scales of longitudinal line.

Dentary in one row with 11–13 (3) conical to tricuspid teeth. Premaxillary teeth in a single row with ten to 11 (3) conical to tricuspid teeth. Premaxillary and dentary teeth increasing in size toward symphysis. Maxillary teeth absent ( Fig. 13 ). Ectopterygoid with minute teeth. Branchiostegals five (2); four attached to anterior ceratohyal and one to posterior ceratohyal. First arch with two gill rakers on hypobranchial (3), six on ceratobranchial (3), one on cartilage between ceratobranchial and epibranchial (3) and five (2) or six (1) on epibranchial. Supraneurals four (3), cartilaginous.

Laterosensory system developmentally truncated, tubules opening in individual pores (i.e. never forming subpores). Supraorbital canal present, posteriorly truncated, associated with the nasal and frontal bones only. Parietal branch of supraorbital canal absent. Preopercular canal present, restricted to the horizontal axis of the pre-opercular bone. Infraorbital, mandibular, otic, postotic, supratemporal canals absent.

Scales cycloid; circuli distributed over entire area of scale. Two to five parallel and well-defined radii present on posterior portion of scale. Trunk lateralline poorly developed, short, visible along first five to seven scales from longitudinal row. No visible pores on scales (except in two specimens, with pores on fifth and seventh scales, respectively). Longitudinal series with 28 (7), 29* (8), 30 (10) or 31 (2) scales. Horizontal scale rows from dorsal-fin origin to lateral line four* (29). Horizontal scale rows from pelvic-fin origin to lateral line four* (26). Scales around caudal peduncle ten (1), 11(3), 12* (21) or 13 (1). Predorsal scales series seven (1), eight* (8), nine (12), ten (4) or 12 (1), covered by skin. Isthmus with scales reaching anteroventral margin of rays. Adipose fin absent. Hypurals one and two fused to each other; hypurals three to six autogenous. Total vertebrae 31 (3); precaudal vertebrae 18 (2) or 19 (1), caudal vertebrae 12 (1) or 13 (2).

cleithrum anteriorly. Scales between anus and anal fin none (6) or one* (24). Anterior portions of scales with vertically oriented superficial neuromasts. Neuromast rows arched anteriorly and more conspicuous on anterior half of body.

Pectoral-fin rays i, ten (2) or 11 (1). Tip of longest pectoral-fin rays anterior to pelvic-fin origin and nearly at vertical through dorsal-fin origin. Pelvic-fin rays i,six,i* (30). Tip of longest pelvic-fin rays slightly anterior to anal-fin origin, close to vertical through last ray of dorsal-fin base. Dorsal-fin rays iii,12,i (3), iii,13,i* (25) or iii,14,i (2); in the three C&S specimens there is a fourth additional anteriormost unbranched ray below the skin, not visible in alcohol-preserved specimens. Distal margin of dorsal fin straight to rounded. Dorsal-fin origin slightly anterior to vertical through pelvic-fin origin. First dorsal-fin pterygiophore located behind neural spine of eighth (1) or ninth (2) vertebrae. Externally visible anal-fin rays ii,six (12) or ii,seven* (18) with distal margin straight to rounded; in three C&S specimens there is a third, small anteriormost unbranched anal-fin ray below skin, not visible in alcohol-preserved specimens. Anal-fin origin slightly posterior to vertical through last dorsal-fin ray. Scales covering base of anteriormost anal-fin rays none (5), one* (22) or two (3). First dorsal anal-fin pterygiophore located behind neural spine of 18 th (2) or 19 th (1) vertebrae. Principal caudal-fin rays i,9,8,i* (2). Caudal fin naked. Five (1) or six (2) dorsal procurrent caudalfin rays and five (3) ventral procurrent caudal-fin Colour in alcohol: Overall background coloration of head and body beige, darker dorsally, with chromatophores densely distributed along two or three dorsalmost series of scales ( Fig. 12 ). Small, dark chromatophores densely concentrated on premaxilla, tip of dentary and maxilla. Head with a dark diffuse stripe extending from tip of snout to dorsal half of opercle, crossing eyes. Ventral portion of head and gular region with silvery tinge and few, scattered, dark chromatophores. Eyes predominantly dark with scattered pigmentation on ventral portion. Suborbital stripe absent. Guanine on ventral portion of opercle, pre-opercle, subopercle and interopercle. Body with one dark, irregularly shaped blotch present immediately posterior to opercle, continuous with a dark midlateral stripe, which extends to tip of median caudal-fin rays. Midlateral stripe encompasses two series of scales vertically, overlapping with dark blotch on its anterior portion and extending to tip of middle caudal-fin rays.

Dorsal-fin coloration sexually dimorphic ( Fig. 12 ). Adult males having dark chromatophores on rays and interradial membranes; chromatophores roughly forming two to five descending dark stripes. Stripes restricted to anterior two-thirds of the dorsal fin, encompassing the first ten to12 dorsal-fin rays. Remaining dorsal-fin area hyaline. Females and immature specimens of both sexes with dorsal fin mostly hyaline, except for few, dark, scattered chromatophores restricted to anterior edge of fin. Pectoral and pelvic fins predominantly hyaline, with few, scattered chromatophores present along margins of rays. Analfin coloration sexually dimorphic. Adult males having three to four ascending, dark, irregular stripes on anal fin formed by chromatophores along rays and interradial membranes. Stripes present on first eight to nine anal-fin rays. Remaining anal-fin area hyaline. Anal fin of females and immature specimens of both sexes with chromatophores restricted to margin of rays and interradial membrane, lacking stripes. Caudal fin mostly hyaline, except of middle caudal-fin rays; dorsal and ventral edge with chromatophores along rays and interradial membranes. Upper and lower caudal-fin base with concentration of brown pigmentation.

Colour in life: Overall body coloration yellowish, darker dorsally ( Fig. 14 ). Abdominal region yellow to silvery. Humeral spot and midlateral stripe usually visible in live specimens. Males and females similar in life coloration. Head yellow dorsally, silver ventrally. Guanine deposits on infraorbitals 2 and 3, cheeks, ventral portion opercular bone, along sub- and interopercle. Upper half of opercle golden. Dentary, premaxillary, and maxillary yellowish.

Dorsal-fin coloration sexually dimorphic.Adult males lacking yellow pigment on the base of the fin and with dark pigments arranged in descending stripes (see ‘Colour in alcohol’). Females and immature specimens of both sexes with proximal portion of interradial membranes yellow from first 11–14 anteriormost dorsal-fin rays and lacking dark pigmentation. Pectoral fin predominantly hyaline and pelvic fin yellowish in both sexes. Yellow pigmentation more concentrated on base of fin rays. Anal-fin coloration sexually dimorphic; adult females with more conspicuous yellow coloration, and adult males with dark blotches forming irregular ascending dark stripes. Pigmentation on females and juveniles of both sexes stronger on base of first five branched anal-fin rays. Caudal fin mostly yellowish, except from middlemost caudal fin rays, with black pigmentation following from dark midlateral stripe.

Sexual dimorphism: Dorsal fin of adult males with two to five conspicuous dark descending stripes, restricted to anterior two-thirds of the fin; anal fin with three or four ascending dark stripes on rays, present along the first eight or nine anal-fin rays ( Fig. 14A ). Females and immature specimens of both sexes with dorsal and anal fins mostly hyaline ( Fig. 14B ). Further details of dimorphic coloration in ‘Colour in alcohol’ section. Bony hooks were not observed on fins of either sex.

Etymology: The specific name rhizophilus is Latinized from the Greek words ρίζα [rhiza], root, and φίλος [philos], friend. The name refers to habitat where the species was collected, in between subaquatic roots of riparian vegetation. It is a declinable adjective.

Geographic distribution: Poecilocharax rhizophilus is known from two localities, both upstream from Paredão Falls, in the Rio Juma, middle Rio Aripuanã drainage, Rio Madeira Basin, Apuí Municipality, Amazonas State, Brazil ( Fig. 10 ).

Ecological notes: Poecilocharax rhizophilus occurs in black (Rio Juma) and clear water (Igarapé Mutum). The type locality is a tributary of the Rio Juma (Igarapé Mutum), that runs through impacted pasture area, at an elevation of 123 m, with swift current, 2–4 m wide, 1–2 m deep and a substrate composed mainly of mud and sand. One specimen was captured in the Rio Juma, which is a black-water river. Different microenvironments were exhaustively sampled during collecting activities, but P. rhizophilus was only captured in the medium-upper water column between subaquatic roots of riparian vegetation ( Fig. 15 ). Other species sampled syntopically with P. rhizophilus were Acestrorhynchus falcatus (Bloch, 1794) , Bario steindachneri (Eigenmann, 1893) , Characidium sp. , Corydoras gracilis Nijssen & Isbrücker, 1976 , Gymnotus coropinae Hoedeman, 1962 , Hemigrammus ocellifer (Steindachner, 1882) , Hoplias malabaricus (Bloch, 1794) , Hyphessobrycon platyodus Ohara, Abrahão & Espíndola, 2017 , H. procyon Pastana & Ohara, 2016 , Moenkhausia comma Eigenmann, 1908 , Otocinclus mura Schaefer, 1997 , Satanoperca jurupari (Heckel, 1840) and Tatia dunni (Fowler, 1945) . The analysis of the stomach contents of three paratypes of P. rhizophilus revealed the presence of Cladocera (Chydoridae) , Chironomidae , unidentified insect fragments and inorganic sediments.

KEY TO THE SPECIES OF CRENUCHINAE

1a. Asymmetrical dark spot on caudal peduncle present; dark midlateral stripe on flanks absent....................2

1b. Asymmetrical dark spot on caudal peduncle absent; dark midlateral stripe on flanks present (sometimes diffuse)…..………................................................................................................................................................3

2a. Adipose fin present; dark blotches on flank absent; posterior terminus of maxilla surpassing vertical through anterior margin of orbit.……………..................................................................… Crenuchus spilurus

2b. Adipose fin absent; dark blotches on flank present; posterior terminus of maxilla never surpassing vertical through anterior margin of the orbit...…................................................................... Poecilocharax callipterus

3a. Two dark, longitudinal stripes positioned dorsally and ventrally along the head and body; anterior and posterior nasal openings separated by a narrow skin fold; presence of nasal flap between anterior and posterior nares………….….……................................................................................ Poecilocharax bovaliorum

3b. One dark, longitudinal stripe positioned on middle of flank; anterior and posterior nasal openings widely separated from each other; absence of a nasal flap….……...............……........................................................4

4a. Suborbital bar present; humeral blotch absent; dimorphic males with dark pigmentation on medial margin of branchiostegal membrane....................................................................................… Poecilocharax weitzmani

4b. Suborbital bar absent; humeral blotch present; dimorphic males lacking dark pigmentation on medial margin of branchiostegal membrane.....................................................................…. Poecilocharax rhizophilus

Conservation assessment: The extinction risk for this species is preliminarily assessed as high. Poecilocharax rhizophilus is a species of restricted geographical range, with an Extent of Occurrence (EOO) of 50 km 2 and known from two localities ( Fig. 10 ). The type locality has moderate riparian forest surrounded by pasture, and the other site is a touristic area (Paredão Falls), intensely impacted by agriculture. There are three Conservation Units surrounding the type locality (Floresta Nacional do Jatuarana to the south, Parque Nacional do Acari to the east and Floresta Nacional do Aripuanã to the west) and there are some preserved, but unprotected areas nearby the type locality. However, the new species was not found elsewhere other than the type locality, despite intense collecting efforts, and it is uncertain if P. rhizophilus is present in these Conservation Units or in other areas. Sampling activities took place in 2015 and 2016, and at that time, the two localities where the species was found (i.e. the Igarapé Mutum and Rio Juma) did not present signs of silting, water turbidity and erosion on the banks ( Fig. 15 ). However, the territory of Apuí has been heavily impacted by deforestation since the discovery of the new species, and it is currently ranked in second place in a list of Brazilian municipalities with greatest loss of native forest ( Fonseca et al., 2021). A continuous decline in the habitat quality is expected and inferred based on erosion, silting and increased turbidity, as results of continued deforestation in the region. There are no estimates of population size or population decline. For these reasons, P. rhizophilus is tentatively assessed Near Threatened (NT) by criterion B2ab(iii) according to the International Union for Conservation of Nature

(IUCN) categories and criteria (IUCN Standards and Petitions Sub-Committee, 2019).

Figures

Figure 10. Type-locality (red square) of Poecilocharax callipterus sp. nov. and P. rhizophilus sp. nov. (blue dot), tributary of the Rio Juma, Rio Aripuanã drainage, Rio Madeira Basin, Apuí, Amazonas, Brazil.

Figure 12. Poecilocharax rhizophilus sp. nov.: A, holotype, male, 20.3 mm SL, MZUSP 121652; B, paratype, male, 23.1 mm SL, MZUSP 121651; C, paratype, female, 23.3 mm SL, MZUSP 121651.

Figure 13. Poecilocharax rhizophilus sp. nov., medial view of premaxilla, maxilla and dentary, right side, MZUSP 121651, paratype, 16.5 mm SL.

Figure 14. Poecilocharax rhizophilus sp. nov., immediately after capture. A, holotype, male, 20.3 mm SL, MZUSP 121652. Paratypes: B, male, 23.1 mm SL; C, female, 23.3 mm SL, MZUSP 121651.

Figure 15. Igarapé Mutum, tributary of Rio Juma, Rio Aripuanã Basin, Apuí, Amazonas, Brazil, type-locality of Poecilocharax rhizophilus sp. nov. Inset details the microenvironment where P. rhizophilus sp. nov. was captured.