4136 (1): 129 140 Articlesymbiont.ansp.org/ixingu/publications/publications/2016... · ·...

ZOOTAXA

ISSN 1175-5326 (print edition)

ISSN 1175-5334 (online edition)Copyright © 2016 Magnolia Press

Zootaxa 4136 (1): 129–140

http://www.mapress.com/j/zt/Article

http://doi.org/10.11646/zootaxa.4136.1.5

http://zoobank.org/urn:lsid:zoobank.org:pub:100BC0A4-08BF-4C1F-8E09-9DE2C5F3ADB4

Oxyropsis ephippia, a New Hypoptopomatine Catfish (Siluriformes: Loricariidae)

from Guyana

ADRIANA E. AQUINO1,3 & MARK H. SABAJ PÉREZ2

1Division of Vertebrate Zoology, American Museum of Natural History, Central Park West at 79th Street, New York, New York,

10024–5192. E-mail: [email protected] Academy of Natural Sciences of Drexel University, 1900 Benjamin Franklin Parkway, Philadelphia, PA 19103.

E-mail: [email protected] author

Abstract

Oxyropsis ephippia, a new species of loricariid catfish in the subfamily Hypoptopomatinae, is described from the Essequ-

ibo and Branco basins, Guyana. Based on the presence of a keel-like row of relatively enlarged odontodes on trunk median

plates immediately above the lateral line canal, the new species is assigned to the genus Oxyropsis Eigenmann & Eigen-

mann 1889. It can be distinguished from its congeners by having the keel-like row on each median plate dominated by a

single odontode (one closest to the posterior margin of the plate) conspicuously larger than preceding ones, and by having

the sides of the trunk below the median series (approximately between median plates 7 to 12) shielded only by plates of

the midventral series, with the exclusion of plates from the ventral series. The report of O. ephippia from the Essequibo is

the first record of the genus in a river system that drains the north-central portion of the Guiana Shield into the Atlantic

Ocean.

Key words: Essequibo, armored catfish, taxonomy, new species, key, distribution

Introduction

Aquino & Schaefer (2002) recognized three species of Oxyropsis Eigenmann and Eigenmann 1889 in theirtaxonomic revision of the genus: two species in the middle and upper Amazon system (O. carinata (Steindachner1879) and O. wrightiana Eigenmann and Eigenmann 1889), and one in the upper Orinoco and rio Negro basins (O.

acutirostra Ribeiro 1951). The latter species occurs in systems draining the Western Guiana Shield and its outliersfurther west (i.e., Colombian Guiana Shield; Funk & Kelloff 2009). Hereby we describe a new species ofOxyropsis based, in part, on the first records of the genus from the Essequibo basin, Guyana, which drains thenorth-central portion of the Guiana Shield into the Atlantic Ocean. The new species is assigned to Oxyropsis based on a shared feature that is autapomorphic for the genus in Loricariidae (Aquino & Schaefer 2002): single row of enlarged odontodes along the trunk midline, lying adjacent and immediately dorsal to the lateral-line canal (Figs.1B–D).

Material and methods

Counts follow Schaefer (1997) and Aquino & Schaefer (2002) (Fig. 2A). Only the right side series of plate countsare included in the table. The series of median dermal plates bears the lateral-line canal. Total lateral plate countsinclude all plates in the median series. The first in the ventral series is a triangular plate between the 4th and 5thplates of the midventral series, above the pelvic fin, and that, unlike adjacent midventral plates, does not articulate1 to 1 with a median plate. Measurements were taken following Buckup (1981) and Aquino & Schaefer (2002) using digital calipers to the nearest 0.1 mm. Throughout the text, BD denotes body depth, HL, head length, CP,

Accepted by M.R. de Carvalho: 23 Dec. 2015; published: 5 Jul. 2016 129

FIGURE 1. Left lateral view of the posterior caudal peduncle of (A) Oxyropsis ephippia, (B) O. wrightiana, (C) O. carinata,

and (D) O. acutirostra. Scale is 1 mm.

AQUINO & PÉREZ130 · Zootaxa 4136 (1) © 2016 Magnolia Press

FIGURE 2. Left lateral view of the trunk plates in (A) O. ephippia, (B) Oxyropsis wrightiana, (C), O. carinata, and (D) O.

acutirostra. Vertical lines identify first plate in corresponding series of trunk plates. Scale is 5 mm.

caudal peduncle, SL, standard length, alc, alcohol preserved specimen(s) and cs, cleared and stained specimen. Theterm marginal odontodes refers to the column of enlarged odontodes on the posterior margin of the trunk dermalplates; the expression ventral canal-bearing plate refers to the large triangular dermal plate of the head locatedventrally between cleithrum and infraorbital bones that bears the terminus of the preoperculo-mandibular canal;compound pterotic is the term applied to the complex of bones located in the temporal region of the head composed of posttemporal, supracleithrum, pterotic, and ossified Baudelot’s ligament; nuchal plate is applied to the plateanterior to the dorsal-fin spine; thoracic plates refers to the dermal plates anterior to the paired cleithra, abdominal

plates to the ventral shield of dermal plates between the pectoral and pelvic fins, and anal plate to the plate betweenthe anus, abdominal plates, and pelvic fins. Throughout the text, fully developed individuals (mature specimens)are recognized by having complete development of abdominal plates, which are the last plates to form duringontogeny. Institutional abbreviations are as listed as in Sabaj Pérez (2010).

Zootaxa 4136 (1) © 2016 Magnolia Press · 131NEW OXYROPSIS EPHIPPIA FROM GUYANA

Oxyropsis ephippia Aquino & Sabaj Pérez sp. nov.

(Figs. 3–5)

Holotype: ANSP 177381, female 42.0 mm SL, Guyana, Burro Burro River (Essequibo Drainage), Deer Falls between Deer Creek and Water Dog Falls, 4°39'53"N, 58°50'28"W, G. Watkins et al., 21 November 1997.

Paratypes (49, 22.3–44.8 mm SL).—Guyana, Essequibo–Atlantic Ocean Drainage: AMNH 265342, 3 (1 cs)29.7–36.7 mm SL, Rupununi River 4.6 km NW of village of Massara, 3°55'34"N 59°16'49"W, M. Sabaj et al., 26October 2002; ANSP 175918, 1, 30.8 mm SL, small creeks crossing Kurupukari–Surama River road ca. 3.0 milesfrom Kurupukari field station, 4°22’29”N 58°50’30”W, W.G. Saul et al., 4 February 1997; ANSP 175919, 1, 29.0mm SL, Essequibo River approximately three hours upstream from Kurupukari field station, 4°34’17”N58°35’17”W, W.G. Saul et al., 3 January 1997; ANSP 175920, 1, 27.0 mm SL, clearwater creek at campsite 3.1miles from Kurupukari field station on Kurupukari–Surama River road, 4°38'0"N 58°42'59"W, W.G. Saul et al., 5February 1997; ANSP 175921, 1, 29.5 mm SL, Essequibo River approximately two hours downstream fromKurupukari field station, 4°47'44"N 58°48'52"W, W.G. Saul et al., 20 January 1997; ANSP 175922, 4, 25.8–27.8 mm SL, Essequibo River, sandbar ca. 800 m downstream from Essequibo campsite (Maipuri), 4°45’43”N58°45’52”W, W.G. Saul, et al., 29 January 1997; ANSP 180659, 3, 26.2–40.5 mm SL, Essequibo River (east bank) at Kurukupari, 4°39'41"N 58°40'31"W, J.W. Armbruster et al., 24 October 2002; ANSP 180662, 3, 22.3–24.7 mm SL, Rupununi River, 3.7 km SSE village of Massara, 3°51'44"N 59°17'4"W, M. Sabaj et al., 27 October 2002;ANSP 180664, 2, 29.5–35.4 mm SL, AUM 35652, 12, 22.5–30.9 mm SL, INPA 50886, 3, 27.7–30.0 mm SL, and ROM 91534, 3, 26.1–29.0 mm SL, same data as AMNH 265342; ANSP 180666, 5, 23.0–25.0 mm SL, SimoniRiver (trib Rupununi), four stations along river from 6.6 km SE to 3.2 km W of Karanambo Ranch, ca. 3°43'9"N59°15'40"W, M. Sabaj et al., 29 October 2002; ANSP 180685, 1, 33.0 mm SL, Araquai Creek (trib Rupununi), 77.3 km SSE of Lethem, 2°45'45"N 59°27'60"W, M. Sabaj et al. 15 November 2003; MCP 49016, 2 alc, 26.2–30.8 mm SL, same data as ANSP 180666; MCP 49017, 2, same data as ANSP 175919.—Branco–Negro–AmazonasDrainage: ANSP 180670, 2, 40.4–44.8 mm SL, Yuora River (trib Ireng, Takutu drainage), 6.7 km NE of village ofKarasabai on road to Tiger Creek village, 4°3'14"N 59°29'7"W, M. Sabaj et al., 31 October 2002.

Diagnosis. Oxyropsis ephippia is distinguished from its congeners by having a keel-like row of odontodesabove the lateral-line canal on each median plate that is dominated by a single odontode (one closest to posteriormargin of plate) conspicuously enlarged, typically one-third to one-half larger (along base-tip axis) than precedingone in same row (Figs. 1A and 4A) (vs.keel-like row immediately above lateral-line with odontodes of roughlyequal size; Figs. 1B–D). It is further distinguished by having the sides of the trunk below the median series,approximately between plates 7 to 12, shielded by plates of the midventral series, with the exclusion of plates fromthe ventral series, which are visible only in ventral view of the trunk (Fig. 2A) (vs. sides of the trunk shielded byplates of the midventral series and ventral series, the latter visible in lateral and ventral views of the trunk; Figs.2B–D).

Oxyropsis ephippia is further distinguished by having 23 plates along the trunk median series (vs. 18–19 in O.

acutirostra and 25–26 in O. carinata and O. wrightiana) and the caudal peduncle in cross section slightlycompressed at the level of the median plates 20–23 (vs. posterior caudal peduncle depressed); from O. acutirostra

by having median series of plates complete (vs. series incomplete; Fig. 2D); from both O. acutirostra and O.

wrightiana by having a deeper caudal peduncle (mean depth 4.8% SL vs. 2.9% and 2.0%, respectively), and shortercaudal peduncle (mean length 36.0% SL vs. 42.4% and 44.4%, respectively); and from O. carinata by having alarger eye (mean orbital diameter 18.2% HL vs. 15.7% HL).

Description. General size small; largest specimen examined 48.7 mm SL. Head and trunk slender, moderatelydepressed (cleithral width 62.5–71.7% HL); greatest body depth at dorsal-fin origin (12.1–14.7% SL), only slightlydeeper than head (11.6–12.7% SL). Dorsal profile straight to slightly convex from tip of snout to dorsal-fin origin(Figs. 3-4). Dorsal profile of trunk straight from dorsal-fin origin to anteriormost procurrent ray of caudal fin. Ventral profile of head and abdomen approximately straight to slightly convex from snout tip to procurrent caudal-fin rays. Dorsal and ventral profiles gently diverging from procurrent towards marginal rays of caudal fin. Snoutsmoothly rounded, parabolic in dorsal view; dorsal rostrum smooth, with paired smooth concavity in region anterior to naris. Dorsal surface between eyes and origin of dorsal fin convex in cross section, flattening caudally. Crosssection of body between pectoral and pelvic-fin origins ovoid, becoming progressively fusiform-shaped (taperingposteriorly) between verticals lines through approximately tip of pectoral fin and median plates 17–18; gradually


compressed at level of 6–7 most posterior median plates; CP mean width 75.5% (range 67.2–91.2%) of CP depth at plates 21–23).

FIGURE 3. Oxyropsis ephippia, ANSP 177381, holotype, 42.0 mm SL, Guyana: Burro Burro River (Essequibo Basin). Photos

by K. Luckenbill and T. Tran.

Eyes moderately large, orbital diameter 17.3–19.9% HL, center of eye positioned closer to posterior tip of pterotic than to tip of snout. Eye dorsolateral on head; fourth infraorbital lateroventral. Tip of adpressed dorsal finreaching vertical through midlength of adpressed anal-fin spine. Pelvic fin not reaching plate anterior to base of anal-fin spine. Pectoral fin reaching vertical through posterior half of pelvic-fin spine length. Serrae (teeth) alongposterior aspect of pectoral-fin spine present, less developed toward basal fifth and distal fifth of spine; bestdeveloped in specimens shorter than about 27.0 mm SL, wherein serrae are conical, moderately acute, each with tiporiented toward base of spine (retrorse); serrae become less conspicuous, more blunt with increasing standard length, and tips variably slanted toward base of spine.

Dermal plates on trunk arranged in five longitudinal rows (Fig. 2A): dorsal series 20; middorsal series 3; median series 23; midventral series 13 (including 4 plates between cleithrum lateral process and first plate of ventral series); ventral series typically 19-20. Ventral plates positioned either lateroventrally (1 to 4 and 11 to 20) or ventrally (5 to 10). Midventral plates deep above ventrally positioned plates in ventral series, shielding side of trunk below median series (Fig. 2A). Lateral line complete, continuous along median series. Midventral plates


articulating with median plates via interlocking digit-like projections; ventral and median plates in contact viaoverlapping smooth edges. Thoracic plates absent. Abdominal plates fully developed at 29 mm SL (development ofplates incipient at about 24–25 mm SL); abdominal plates arranged in paired series of 5–9 elongate lateral platesand medial series of 4–9 polygonal plates; three or more polyhedral plates posterior to pectoral girdle; patch of small polyhedral plates between abdominal series and anal plate. Single anal plate. Canal-bearing plate betweencleithrum and infraorbital bones well developed, mostly ventral except for posterior ventro-lateral portion in contactwith opercle, and with lateral pore of canal close to pore of infraorbital canal between infraorbital plates 4 and 5.

Odontodes uniformly small and evenly distributed dorsally on head, progressively arranged in longitudinalrows toward sides and dorsum of trunk. Subtle keel-like longitudinal row of odontodes immediately above lateral-line canal on each median plate is dominated by single odontode (close to posterior plate margin above pore of lateral-line canal) that is conspicuously enlarged, typically one-third to one-half longer (along base-tip axis) than preceding one in same row (Fig. 1A); keel-like row most noticeable in dorsal view of trunk between median plates8 and 18. Enlarged odontode usually paired with similarly enlarged odontode below lateral-line canal.

Midventral plates 8 to 13 with area of slightly enlarged odontodes, particularly along margin of plates; odontodes less noticeable with increasing SL. On ventral side of body, odontodes tightly and evenly arranged overventral canal-bearing plates, abdominal plates, anal plate, and ventral series of plates posterior to anal plate.Odontodes on ventral margin of pelvic-fin spine enlarged; odontodes on ventral margin of pectoral-fin spinemoderate in size.

Anterior tip of rostral plate with narrow pad of soft tissue; odontodes dorsal and ventral to tip irregularlyarranged. Anterior and lateral rostral snout plates not noticeably reflected ventrally. Nuchal plate width about 2.5 times width of dorsal-fin spine at origin.

Teeth small, slender; premaxillary teeth 19–27, mandibular teeth 16–26. Oral disk round, papillose. Maxillarybarbels present, short. Dorsal fin i,7; pectoral fin i,6; pelvic fin i,5, anal fin i,5. Adipose fin absent.

Sexual dimorphism. Male genital papilla present. In males, odontodes small and tightly packed on plates 2–4 of trunk ventral series, lateral to anal plate and anus region; odontode arrangement more spaced on anal plate andon plates between anal fin and anus. In females, distribution of odontodes on same ventral plates not noticeablydifferent from patterns on adjacent plates.

Coloration. Ground color in ethanol tan (Figs. 3–4). Dark brown punctiform epidermal melanophores in smallclusters irregularly distributed on dorsal and lateral portions of head (Fig. 4), sometimes leaving pale middorsalregion on snout (Fig. 3). Dark brown deep-lying punctiform melanophores roughly arranged in six middorsalblotches (typically, one anterior to dorsal fin, one at base of dorsal fin, and four posterior to dorsal fin). Brownmidlateral stripe through cleithrum lateral process, along trunk median and midventral series of plates to base ofcaudal fin; stripe more diffuse posteriorly, variably connected to darkened lanceolate plates at base of caudal fin. Dorsal portion of cleithrum lateral process, in contact with first midventral plate, dark brown.

Ventral surface of head and trunk, between posterior lip and anus, pale, scarcely pigmented. Punctiformmelanophores concentrated on anterior lip, extended laterally to barbels; scattered at bases of anal, pectoral and pelvic fins. Uneven sprinkling of deep-lying dark melanophores over ventral canal-bearing plates and along ventral series of plates.

Caudal-fin with 6–7 vertical bands of brown melanophores restricted to fin rays; proximal bands variablycoalesced into darker, slightly asymmetrical blotch on basal lower half of caudal fin; basal blotch variablyconnected with dark lanceolate plates (Fig. 5A). Other fins with faint dark bands along anterior edge of spine,continuous with diffuse bands on branched rays (roughly, 8–9 bands on dorsal fin, 3–4 on anal fin, five on pectoralfin, and three on pelvic fin). Interradial membranes of all fins clear, unpigmented.

Distribution. Oxyropsis ephippia is recorded from Guyana (Fig. 6) on both sides of the shallow divideseparating the Essequibo watershed (Atlantic Drainage) from the Branco (Negro–Amazonas Drainage). In theEssequibo Basin, it is known from the mainstem Essequibo, and two of its left bank tributaries (Burro Burro,Rupununi, and their tributaries). In the Branco Basin it is know from the Yuora River, a small tributary of the Irengdraining the southeastern limits of the Pakaraima Mountains.

The cichlid Guianacara dacrya described by Arbour & López–Fernández (2011) occurs in many of the samestreams (e.g., Burro Burro, Rupununi and Yuora), and shares a similar distribution pattern on both sides of theEssequibo–Branco divide. The two watersheds are intermittently connected in wet years (between May and September) when the Rupununi savannas between the Pakaraima and Kanuku mountains becomes a vast floodedplain known as Lake Amaku (Lowe–McConnell 1964).


TABLE 1.

Holotype N Range Mean sd

Standard length 42.0 12 25.2 44.8 36.2 5.7

PERCENT OF STANDARD LENGTH

Predorsal length 41.4 11 40.1 44.5 42.9 1.3

Head length 29.8 11 29.4 33.5 31.2 1.5

Body depth 13.5 11 12.1 14.7 13.5 0.8

Dorsal-fin spine length 27.6 9 24.2 26.2 25.3 0.8

Trunk length 46.2 11 44.8 48.0 45.9 1.0

Pectoral-fin spine length 23.9 11 22.0 24.4 23.0 0.7

Abdominal length 16.0 11 11.6 16.8 15.1 1.3

Caudal peduncle length 35.4 11 33.3 38.5 36.0 1.7

Caudal peduncle depth 5.0 11 4.3 5.3 4.8 0.3

Head depth 11.9 11 11.6 12.7 12.1 0.4

Snout length 15.8 11 15.4 17.6 16.5 0.6

Horizontal eye diameter 5.4 11 5.2 6.3 5.7 0.3

Least orbit-nare distance 2.2 11 1.9 2.4 2.2 0.2

Dorsal least interobital distance 15.4 11 14.1 16.0 15.0 0.6

Ventral least interobital distance 17.7 11 16.7 18.5 17.7 0.6

Cleithral width 20.6 11 19.4 21.6 20.6 0.6

Head width 18.2 11 16.6 18.5 17.9 0.5

Interpelvic distance 9.5 11 8.6 10.5 9.7 0.6

PERCENT OF HEAD LENGTH

Body depth 45.5 11 37.6 49.6 43.5 3.8

Head depth 39.9 11 34.8 43.0 38.9 2.8

Snout length 52.9 11 51.1 56.7 53.0 1.7

Horizontal eye diameter 18.1 11 17.3 19.9 18.2 0.7

Least orbit-nare distance 7.4 11 5.9 8.0 7.0 0.8

Dorsal least interobital distance 51.7 11 43.0 54.2 48.2 3.6

Ventral least interobital distance 59.3 11 52.3 62.4 56.9 2.9

Cleithral width 69.1 11 62.5 71.7 66.1 2.8

Head width 61.1 11 53.9 61.9 57.4 2.3

Interpelvic distance 31.8 11 28.6 32.9 31.0 1.3

LATERAL SERIES OF PLATES

Dorsal series 19 11 18 20 18.9 0.8

Middorsal series 3 11 3 3 3.0 0.0

Medial series 23 11 23 23 23.0 0.0

Midventral series 9 12 9 11 9.4 0.7

First midventral series 4 11 4 4 4.0 0.0

Ventral series 19 10 19 20 19.1 0.3

ABDOMINAL SERIES OF PLATES

Right lateral series 6 11 5 10 7.1 1.7

Left lateral series 7 11 5 10 7.1 1.9

Medial series 6 10 4 8 7.1 1.3

TEETH

Premaxillary teeth 27 11 19 27 22.1 2.2

Dentary teeth 26 10 16 26 19.0 2.5


FIGURE 4. Oxyropsis ephippia, ANSP 180670, paratype, XX mm SL, Guyana: Yuora River (trib Ireng, Takutu–Branco–Negro

Dr., Amazon Basin).

Habitat. Oxyropsis ephippia generally inhabits small to medium-sized streams with moderate current and riparian forest; water ranges from moderately turbid (e.g., Essequibo mainstem), to clear (Yuora), to black (BurroBurro). A variety of substrates are found at most collecting localities, sand being particularly common.

Etymology. The specific epithet ephippia (L. ephippium, Gr. ephippion, meaning saddle) refers to the saddle-like middorsal blotches.

Discussion

Species of Oxyropsis are sympatric with similar-looking species of Hypoptopoma, and both genera are members of the loricariid subfamily Hypoptopomatinae (sensu Roxo et al. 2014). For example, O. ephippia was collected withH. guianensis in the Rupununi River and its tributary the Simoni in Guyana. Oxyropsis wrightiana and H.

psilogaster occur in proximity in the lower río Nanay basin, a moderate blackwater tributary to the río Amazonas in Peru. Oxyropsis wrightiana, however, appears restricted to small tributary creeks whereas H. psilogaster occursover sandy beaches in the main channel of the Nanay.

Diagnostic features of the Oxyropsis aside, abdominal plating and caudal fin pigmentation can be useful to distinguish sympatric species of Oxyropsis and Hypoptopoma. In both genera, the abdomen becomes fully plated in adults (Aquino & Schaefer 2002; 2010); however, Oxyropsis matures at a smaller size. Accordingly, O. ephippia

has abdomen fully plated, medial abdominal plates wide, contacting lateral ventral plates in specimens >29 mm SL


(Figs. 3–4) vs. medial abdominal plates reduced, leaving unplated gaps on either side in specimens of H.

guianense <41.5 mm SL. Similarly, specimens of O. wrightiana >40 mm SL have wide medial abdominal platescontacting lateral ventral plates vs. medial abdominal plates highly reduced or lacking entirely, leaving abdomennaked in specimens of H. psilogaster <47 mm SL.

Subtle differences in caudal-fin pigmentation also exist between the aforementioned species (Fig. 5). In O.

ephippia, the caudal fin has 6–7 faint vertical bands of brown melanophores restricted to fin rays with proximal bands variably coalesced into darker, slightly asymmetrical

blotch on basal lower half of caudal fin (i.e., lower half of 2–3 most proximal bands more intensely pigmented;Fig. 5A). In H. guianense, the caudal fin typically has fewer (≤5), wider brown bands that coalesce along themiddle rays and membranes, forming an elongate blotch; the lower half of each band appears darker withmelanophores occurring on both the rays and membranes, and the distal tips of the upper and lower caudal lobes aresomewhat darkened (Fig. 5C). In O. wrightiana, the caudal fin has 3–4 wide vertical bands of brown melanophoreswith lower half of two most proximal bands coalesced into a darker, slightly asymmetrical blotch; melanophoresoccur on both the rays and membranes in the proximal bands, but are restricted to the rays of in the distal bands(Fig. 5B). In H. psilogaster, the vertical bands are scarcely evident in adults, and the pigmentation pattern isdominated by a dark elongate blotch on the middle rays and membranes, a large dark blotch on the distal lowerlobe, and a smaller dark blotch on the distal upper lobe (Fig. 5D).

There are noteworthy convergences in coloration, morphology and habitat between Oxyropsis ephippia and aspecies of hillstream lizard loach in the Asian genus Balitoropsis (Cypriniformes: Balitoridae). For example, O.

ephippia and Balitoropsis ophiolepis (Bleeker 1853) share six dark brown middorsal saddles and dark bands in themedial and paired fins (see Fig. 11 in Randall & Riggs 2015:220). Shared morphological features include smallsize, depressed head with elongate, parabolic snout, ventral mouth, ventrally flattened body, and a long and slendercaudal peduncle. Balitoropsis also has scales highly textured with longitudinal keels, up to eight keels per scale(Randall & Riggs 2015); the central keel of each scale is enlarged and aligned along the dorsal, lateral and posteriorventral sides. In Oxyropsis, odontodes on the plates are aligned to form longitudinal keels, effecting a similarsurface texture. In Oxyropsis, the vent is located near the center of its standard length, midway between the origins of the pelvic and anal fins. In Balitoropsis, the vent is closer to midbody than in other balitorins (i.e., nearer to pelvic-fin base vs. anal-fin origin; Z. Randall, pers. comm. 2015). Balitoropsis and Oxyropsis both occur in relatively small tropical streams in southeastern Asia and cis-Andean South America, respectively, and are often associated with woody debris in swift flowing water. The parent taxon of balitorids, order Cypriniformes, isentirely absent from South America whereas the parent taxon of Oxyropsis, family Loricariidae, is endemic to Central and South America. Accordingly, characteristics shared by Oxyropsis and Balitoropsis may represent a“globally distributed, strong evolutionary convergence” as discussed by Winemiller et al. (2015). In light of theniche classification scheme advanced by Winemiller et al. (2015), one would predict that O. ephippia and B.

ophiolepis share a discrete niche defined by a particular combination of functional traits associated with life history,trophic position, habitat, defense and metabolism.

Key to the species of Oxyropsis

1 Median plate series truncated, 18–19 plates along median series (Fig. 2D); caudal peduncle extremely shallow, depth 1.8–2.2%

SL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. acutirostra Ribeiro

(Upper Orinoco basin; upper and lower Negro, Amazon basin)

- Median plate series complete, 23–26 plates along median series; caudal peduncle depth greater than 2.5% . . . . . . . . . . . . . . . 2

2 Plates along median series 23 (Fig. 2A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. ephippia Aquino & Sabaj Pérez sp. nov.

(Essequibo basin; trib Ireng, Takutu–Branco–Negro drainage, Amazon basin)

- Plates along median series 25–26 (Figs. 2B–C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 Caudal peduncle depth 2.5–3.7% SL (22.6–30.8% BD); 15–26 premaxillary teeth, 15–24 . mandibular teeth; last four median

series plates with 1–2 rows of odontodes above and below mid-lateral row of enlarged odontodes (Fig. 1B) . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. wrightiana Eigenmann and Eigenmann

(Middle and upper Amazon basin)

- Caudal peduncle depth 3.8–4.6% SL (29.5–35.8% BD); 30–40 premaxillary teeth, 25–35 . mandibular teeth; last four median

series plates with 5–6 rows of odontodes above and below mid-lateral row of enlarged odontodes (Fig. 1C) . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. carinata (Steindachner)

(Middle and upper Amazon basin; lower Negro, Amazon basin)


FIGURE 5. Pigmentation pattern in caudal fin of (A) Oxyropsis ephippia, 29.1 mm SL (ANSP 180664) (B) Oxyropsis

wrightiana, 50.1 mm SL (ANSP 178336), (C) Hypoptopoma guianense, 41.4 mm SL (AUM 35652), (D) Hypoptopoma

psilogaster, 34.9 mm SL (ANSP 180658). Vertical line points to enlarged odontode on posterior margin of median plate,

immediately dorsal to pore of lateral-line canal. Scale is 5 mm. Photos by K. Luckenbill and T. Tran.


FIGURE 6. Drainage map of northern South America showing distribution of species of Oxyropsis (modified from Aquino &

Schaefer, 2002). Symbols may indicate more than one collection locality; open symbol represents type locality of O. ephippia.

Comparative Material

(Additional examined material listed in Aquino & Schaefer, 2002).

Hypoptopoma guianense: (all specimens from Guyana) AUM 35652, 3, Rupununi River 4.6 km northwest of Massara, 3.92603°N 59.28037°W; AUM 35658, 26, Simoni River, 3.71917°N, 59.26121°

Hypoptopoma psilogaster: (all specimens from Peru, Loreto) ANSP 174917, 1, stream ca. 70 km south of Iquitos, 5°0’S 73°38’W; ANSP 178335, 2, río Itaya at Iquito–Nauta hwy bridge; ANSP 180658, 26, río Nanay near Santa Clara, 3°46’45”S, 73°22’06”W; ANSP 182470, 1, río Nanay at Pampa Chica, 3°45’09”S 73°17’0”W; ANSP 193203, 1, río Nanay 7 km west of Iquito, 3°45’6”S 73°18’26.3”W.

Oxyropsis acutirostra: ANSP 192451, 22, Colombia, Guainía, río Inirida, caño Caranacoa, upstream of Puerto Inirida, 3°45.6’N 67°58.7’W; ANSP 180816, 1, ANSP 191366, 1, Venezuela, Amazonas, caño Marujeta, tribVentuari, 4°17’41.3”N 66°17’19.97”W; ANSP 196771, 9, Venezuela, río Guapuchi, trib Ventuari, 4°7’49”N66°45’14”W; AUM 43090, 1, Venezuela, Amazonas, caño Grulla, trib Orinoco, 4°43’48”N 67°49’8”W.

Oxyropsis wrightiana: (all specimens from Perú, Loreto) ANSP 176154, 1, creek trib to río Momon, NanayDr., 3°42’S 73°13’W; ANSP 178336, 3, río Yanayacu, 25 miles south of Iquitos; ANSP 191997, 1, caño Shirui, trib río Nanay, 3°45’5”S 73°17’24.8”W; ANSP 193942, 1, Moena caño and mouth of Ullpa caño near Iquitos,3°46’19”S 73°14’16”W.


Acknowledgments

We thank the following individuals and institutions for relevant information and field assistance: C. Allison, J.Armbruster, N. Lujan, and D. Werneke (AUM), W. Eschmeyer (CAS), R. Ota, M. Rocha (INPA), E. Holm (ROM), M. Thomas (SIUC), Z. Randall (UF), and M. Hardman. Thanks to Kyle Luckenbill (ANSP) and Trung Tran (Drexel University) for photographic assistance. AEA also thanks B. Brown and S. Schaefer (AMNH) for their support in her research. Project supported in part by grants to MHSP from U.S. National Science Foundation(DEB–0315963, DEB–1257813).

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