Liosomadoras oncinus (Jardine, 1841)

Birindelli, José L. O. & Zuanon, Jansen, 2012, Systematics of the Jaguar catfish genus Liosomadoras Fowler, 1940 (Auchenipteridae: Siluriformes), Neotropical Ichthyology 10 (1), pp. 1-11 : 2-6

Liosomadoras oncinus (Jardine, 1841) Figs. 1-2

Arius oncinus Jardine in Schomburgk, 1841: 173, plate 4 [type locality: rio Padauiri ; no types known].

Arius oncina Jardine in Schomburgk, 1841: figure legend of plate 4 [misspelled]. - Eigenmann & Eigenmann, 1890: 266 [considered a doubtful species of Centromochlus ]. - Mees, 1974: 59 [name included in a footnote removing the species from Centromochlus and Tatia ].

Centromochlus oncinus Gosline, 1945: 10 [catalog, new generic combination].

Liosomadoras oncinus Mees, 1978: 270 [redescription, new generic combination]. - Burgess, 1989: 241 [ornamental fish catalog]. - Eschmeyer, 1998: 1241 [catalog]. - Ferraris, 2003: 475 [catalog]. - Ferraris, 2007: 75 [catalog]. - Akama & Soares-Porto, 2007: 118 [catalog, incorrectly assigning L. oncinus for Suriname and Peru].

Diagnosis. Liosomadoras oncinus is readily distinguished from L. morrowi by differences in color pattern. Liosomadoras oncinus has two longitudinal rows of about seven large squarish dark-brown blotches on the body in small specimens (up to 60 mm SL), which become pale in the center, in larger specimens. In even larger specimens, the blotches start to fragment into opened blotches and, eventually (in specimens of 100 mm SL or more), in widespread small spots, some still forming a fragmented open square (vs. widespread, non-organized, dark round blotches on body in specimens of all sizes), and for having a pale midlateral line on body, without dark blotches (vs. midlateral line of body colored as the remaining lateral portion of body).

J. L. O. Birindelli & J. Zuanon 3

portion of body (pleuroperitoneal) cavity; apple-shaped or abbreviated cordiform with internal T-shaped septum ( Birindelli et al., 2009: fig. 2).

Description. Morphometric data for Liosomadoras oncinus is presented in Table 1. Species moderately sized (reaching up to approximately 150 mm SL) with a somewhat depressed head and compressed body, especially posteriorly; mouth terminal, with prognathous jaw. Eye relatively small, anterolaterally positioned on head; posterior cleithral process long, shallow, with several rows of spines. Dorsal-fin rays II,6 (n = 25); pectoral-fin rays I,6 or 7 (mode 6, n = 25); pelvic-fin rays i,6 (n = 25); anal-fin rays iii,11 or 12 (mode 11, n = 25); caudal-fin rays i,7,8,i (n = 25). Dorsal-fin spine robust, with approximately 20 strong spines on anterior face and about 10 weak spines on posterior face; pectoral-fin spine robust, with strong spines on both anterior and posterior faces. Axillary pore with single opening, located immediately ventral to base of posterior cleithral process. Adipose fin thick, with base slightly larger than anal-fin base. Anal fin short, with lobe length slightly greater than base length. Lateral line complete, straight to slightly sinuous anteriorly, unbranched at caudal fin, few transverse rows of free neuromasts dorsal to lateral-line canal, usually visible as clear areas on body. Caudal fin weakly forked, ventral lobe slightly larger than dorsal one. Gas bladder occupying most of dorsal Osteology. Lateral and dorsal view of head in Fig. 3 . Cranial-roof bones and nuchal plates well developed and ornamented with shallow grooves and reticulated ridges. Dorsal surface of cranial-roof bones straight in lateral view, and slightly convex in frontal view, especially at nuchal region.

Mesethmoid short and wide, bifid anteriorly with cornua anterolaterally oriented, posteriorly contacting frontals (not enclosing fontanel). Mesethmoid anteriorly covered by thick skin, its middle and posterior portion covered by a thin layer of skin. Anterior cranial fontanel rounded or divided into a smaller opening anteriorly, delimited by frontals. Posterior cranial fontanel completely occluded.

Premaxilla plate-like with many minute, acicular teeth closely set in multiple, irregular rows; attached dorsally to mesethmoid cornua. Maxilla short, proximal end with hollow condylar process at base of maxillary barbel. Autopalatine short, rod-like. Nasal long, tubular, running from anterior tip of mesethmoid to suture between mesethmoid and frontal; also, possessing small laterally oriented branch located at approximately the anteriormost one-fourth of the bone.

Lateral ethmoid broad, contacting first infraorbital anterolaterally, mesethmoid medially and frontal posteromedially; covered by thick skin, except for outer margin near perimeter of orbit. Sphenotic large, contacting lateral ethmoid, thus excluding frontals from orbit. Epioccipital with a small lateral border enclosing tympanic area, and short, weakly defined posterior process. Posttemporo-supracleithrum subtriangular, V-shaped ventral margin, tip articulating with dorsal process of cleithrum; conspicuous pitline in area near suture between pterotic and epioccipital; contacting only pterotic, and epioccipital (falling short from reaching middle nuchal plate).

Nuchal shield formed by anterior, middle and posterior nuchal plates, ventrally fused with neural spines of the 4 Systematics of the Jaguar catfish genus Liosomadoras complex vertebrae. Anterior nuchal plate pentagonal, with apex pointed posteriorly; anterior nuchal plate sutured to parieto-supraoccipital anteriorly, epioccipital laterally and middle nuchal plate posteriorly. Middle nuchal plate butterflyshaped, anteriorly sutured to anterior nuchal plate, and epioccipital. Lateral margins of middle nuchal plate concave. Posterior nuchal plate with lateral wings ventrally expanded; posteroventral portion attached to the infranuchal ligament (latter attached to the first rib). Tympanic area delimited by posttemporo-supracleithrum anteriorly, posterior cleithral process ventrally, middle nuchal plate dorsally and posterior nuchal plate plus infranuchal ligament posteriorly ( Fig. 4 ).

Four infraorbitals. First infraorbital broad, with smooth anterior expansion, medially pointed towards anterolateral cornu of mesethmoid and laminar posteromedial expansion participating in orbital perimeter. Second, third and fourth infraorbitals tubular, with bony granulations on lateral face.

Dentary with teeth similar in form and arrangement to those present on premaxilla. Dentary with six ventral openings for the preoperculomandibular laterosensory canal. Coronomeckelian bone small and connected posteriorly to angulo-articular and laterally to dentary (not connected anteriorly to dentary), covering part of Meckelian cartilage.

Metapterygoid roughly trapezoidal, articulating with quadrate ventrally and hyomandibula posteriorly and to entopterygoid anterodorsally. Entopterygoid small, situated between metapterygoid and lateral ethmoid. Hyomandibula broad, dorsally articulated to sphenotic and pterotic. Quadrate relatively large, sutured to metapterygoid, hyomandibular and preopercle, and articulated with angulo-articular. Suprapreopercle absent. Opercle roughly triangular, with broad posterior border.

Urohyal relatively small, longer than wide, with strong ventral keel, and without lateral wings. Ventral hypohyal larger than dorsal hypohyal ( Fig. 5 ); with small suture to anterior ceratohyal laterally. Anterior ceratohyal elongate, joined to posterior ceratohyal laterally via suture and medially via synchondral joint. Seven branchiostegal rays; first four articulated with the anterior ceratohyal, and last three with the posterior ceratohyal. Basibranchials 2 and 3 ossified with cartilaginous caps, the former broad and the latter elongate. Basibranchial 4 entirely cartilaginous, roughly hexagonal. Three hypobranchials, first two partially ossified, third (posteriormost) entirely cartilaginous; first hypobranchial rod-like, with cartilage caps restricted at medial and lateral end. Five ceratobranchials ossified, elongate, with cartilaginous caps at both ends; fifth ceratobranchial with middle portion broad, bearing lower pharyngeal plate with many acicular teeth. Four or five epibranchials, first two elongate, third with well-developed uncinate process posteromedially oriented, fourth possessing small dorsal expansion; fifth epibranchial greatly reduced and cartilaginous (INPA 35453), or entirely

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absent (MZUSP 93497). Pharyngobranchials 1 and 2 absent. Cartilaginous nodule joining medial ends of epibranchials 1 and 2 and anterior tip of pharyngobranchial 3. Pharyngobranchials 3 and 4 ossified; third elongate, with posterior extremity broad; fourth short and broad. Upper pharyngeal tooth plate oval, bearing many ventrally directed acicular teeth. First four gill arches with two rows of approximately 15 minute rakers; last gill arch with only an anterior row of approximately eight rakers.

Total vertebrae 39 (n = 2) or 40 (n = 1). Complex vertebra completely sutured to fifth, sixth, and seventh vertebrae, and partially to eighth vertebra; first completely free vertebra is ninth. Aortic passage enclosed by superficial ossification (n = 3), and ventrally keeled. Müllerian ramus round, broad, oriented about 45° to longitudinal body axis. Vertebra 5 with pair of process-like parapophyses directed posterolaterally. Vertebrae 6 to 14 or 15 bearing ribs.

Pectoral girdle strong, broad, with well-developed dorsal, posterodorsal, and posterior processes of cleithrum, and relatively short coracoid process ( Fig. 6 ). Posterior cleithral process elongate (length more than six times depth), ornamented with denticulate longitudinal ridges. In ventral view, girdle completely covered by muscle layers. Bony crest (keel) on ventral surface of coracoid oriented at approximately 45° to longitudinal axis of body, separating abductors superficialis and arrector ventralis muscles. Two proximal radials ossified, elongate, rod-like. One or two distal radials cartilaginous (hardly visible in the examined cs specimens). Pectoral spine with antrorse serrations along anterior margin and retrorse along posterior margin.

Basipterygium subtriangular ( Fig. 7 ), external and internal anterior processes long, roughly straight, rod-like; external process longer. Lateral process weakly developed. Posterior process small, short, ossified. Cartilaginous cap along medial, posterior and posterolateral margins of basipterygium.

Anal fin with12-13 pterygiophores ( Fig. 8 ), all rod-like except last one, broad and supporting 2-3 rays. Caudal skeleton with parhypural, hypural 1 and hypural 2 fused, forming a single ventral plate, which is in turn fused to compound centrum ( Fig. 9 ). Hypural 3 and 4 fused, but not fused to compound centrum; hypural 5 independent. Hypurapophysis of type C following Lundberg & Baskin (1969).

Coloration. Ground color tan to cream laterally and brown dorsally; sometimes more yellowish, other times grayish. Small specimens (up to 60 mm SL) with two longitudinal rows of about seven large squarish dark-brown blotches on body and smaller blotches on head and fins. In larger specimens, blotches become pale inside and start to fragment into opened blotches and then, eventually, into widespread small spots, some still forming a fragmented open square (in specimens of 100 mm SL or more; Fig. 2 ). Midlateral line of body pale, without dark blotches, from tympanic area to caudal-fin base. Neuromasts of lateral line and transversal lines dorsal to lateral line with pale border. Ventral portion of head and abdomen pale cream, usually without spots, or rarely with few dark spots.

6 Systematics of the Jaguar catfish genus Liosomadoras

Coloration in live specimens very similar to that described above based on alcohol-preserved specimens, except that live specimens have more conspicuous dark blotches over pale yellow background.

Sexual dimorphism. Nuptial males of Liosomadoras oncinus exhibit the dorsal fin with an irregular row of serrations on the anterior face and the capacity of moving it far forward, at an angle of more than 90°. As in other Auchenipterinae , nuptial males of Liosomadoras oncinus also have the genital papilla as a tube attached to the anterior border of the anal fin and opening at the distal edge of last unbranched ray.

Distribution. Liosomadoras oncinus is known from the rio Negro basin (including rio Branco) from Barcelos, Amazonas upstream to near the mouth of rio Içana, in Brazil, and upper rio Orinoco in the río Ventuari, río Casiquiare and río Atapabo, in Venezuela ( Fig. 10 ). Royero (1999) listed specimens of Liosomadoras oncinus collected in the río Casiquiare (MBUCV 26062;MCNG 12150), and its tributaries río Siapa (MCNG 12309, MCNG 25970)and río Pasimoni(MAC-PAY 2295,MCNG 12437).

Ecology. There is no comprehensive published information on the biology and ecology of Liosomadoras oncinus in its natural habitat. Specimens collected by us were found in cavities and nooks of submerged tree trunks of black water rivers, such as rio Negro, and swamp forest (igapós) of clear water rivers, such as río Ventuari. Aquarium observations indicate that the species is carnivorous.

Etymology. Named in reference to the overall color pattern, noticeably similar to the color pattern of the South American Jaguar Panthera onca .

Figures

Fig. 1. Schomburgk’s original drawing of Arius oncinus (Schomburgk, 1841: Fig. 4).

Fig. 2. Liosomadoras oncinus: (a) specimen purchased on theAquarium trade in Montreal (photo by Oliver Lucanus); (b) and (d) AUM uncatalogued, collected with MZUSP 105828 (photo by Nathan Lujan); (c) MZUSP 105828 (nuptial male), río Ventuari, Orinoco basin. All photographed live.

Fig. 3. Head in dorsal (a) and lateral (b) view of Liosomadoras oncinus,MZUSP105828,99mmSL.AAR=angulo-articular,acf anterior cranial fontanel; ANP anterior nuchal plate, CLE = cleithrum,COR=coracoid,DEN =dentary,ENT= entopterygoid, EPO = epioccipital, FRO= frontal,HYO = hyomandibular, IO= infra-orbital, IOP = interopercle,LET = lateral ethmoid,MAX = maxilla, MES = mesethmoid, MNP = middle nuchal plate, Mr Müllerian ramus, MTP = metapterygoid, OPE = opercle, PNP = posterior nuchalplate,POP =preopercle,PTO = pterotic,QUA = quadrate, SCL = posttemporo-supracleithrum, SOC = parietosupraoccipital,SPO = sphenotic.Scale bar = 5 mm.

Fig. 4. Tympanic area in lateral view of Liosomadoras oncinus, MZUSP 93497, 74.8 mm SL.Scale bar = 10 mm.

Fig. 5. Schematic illustration of the hyoid and branchial arches in dorsal view of Liosomadoras oncinus, based on MZUSP 93497, 70.7 mm SL. Left side of dorsal branchial arches omitted for ease of understanding. Urohyal and branchiostegal rays not represented. AC = anterior ceratohyal, BBn basibranchials, CBn = ceratobranchials, cn = cartilaginous nodule, DH = dorsal hypohyal, Epn = epibranchials, HBn = hypobranchials, IH = interhyal, PBn = pharyngobranchials, PC = posterior ceratohyal, UPTP = upper pharyngobranchial tooth plate, VH = ventral hypohyal. Scale bar = 5 mm.

Fig. 6. Pectoral girdle in ventral view of Liosomadoras oncinus, MZUSP 105828, 99 mm SL. Scale bar = 5 mm.

Fig. 7. Schematic illustration of the pelvic girdle in dorsal view of Liosomadoras oncinus, based on MZUSP 105828, 101 mm SL.Scale bar = 5 mm.

Fig.8.Anal fin in lateral view of a nuptialmale ofLiosomadoras oncinus, MZUSP 105828, 99 mm SL. Scale bar = 5 mm.

Fig.9. Caudal skeleton in lateral view of Liosomadoras oncinus, MZUSP 105828, 99 mm SL. EP = epural, H = hypurapophysis, HS = hemal spine, HY = hypural, NS = neural spine, PH = parhypural, PS = pleurostyle, PU1+U1 = fused first preural and first ural centra, PU2 = second preural centra.Scale bar = 5 mm.

Fig. 10. Distribution of the species of Liosomadoras, L. oncinus represented by yellow circles, and L. morrowi by red squares. Type locality represented by open symbols.