Paracanthopoma cangussu Henschel, Katz & Costa 2021
Creators: name: Pinna, Mário de
name: Dagosta, Fernando Cesar Paiva
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Siluriformes
Trichomycteridae
Paracanthopoma
Paracanthopoma cangussu

description: Paracanthopoma cangussu Henschel, Katz & Costa, 2021
(Fig. 11)
Paracanthopoma cangussu Henschel, Katz & Costa, 2021a: 3, figs. 1-2 [holotype: UFRJ 12696, 11.8 mm SL; type locality: Brazil: Tocantins State: Pium Municipality: sandbank at a beach in the Bananal Island, Javaés River drainage, Araguaia River basin, 09°59′52″S, 50°06′49″W].
Material examined
All from Brazil: INPA 16558, 3 ex, 14.4-16.2 mm SL, no data; MZUSP 94982, 15 ex, 14.2-17.5 mm SL, Brazil, Parque Estadual do Cantão, rock pool in rio Araguaia, col., unknown, Jan 2006; MZUSP 86236, 39 ex (7 mol), 12.2-14.6 mm SL, Mato Grosso, Cocalinho, Corixo da Saudade (= Corixinho, trib. to rio Araguaia), 25 km NW of Cocalinho by road MT-326 (14°17′20.6″S, 51°09′12.1″W), col., O. Oyakawa, 13 Oct 2004; MZUSP 86250, 8 ex (2 c&s), 12.5-17.3 mm SL, Mato Grosso, Cocalinho, rio Cristalino (trib. to rio Araguaia), 47 km from Cocalinho by road MT-326 (14°12′45″S, 51°18′21″W), col., J.L. Birindelli et al., 14 Oct 2004; MZUSP 86257, 6 ex, 12.4-14.1 mm SL, Mato Grosso, Cocalinho, Ribeirão Água Preta (trib. to rio Cristalino, rio Araguaia drainage), approx. 79 km NW of Cocalinho by road MT-326 (14°08′57″S, 51°32′21″W), col., C. Moreira, 14 Oct 2004; MZUSP 86271, 40 ex (4 c&s), 12.0- 15.3 mm SL, Mato Grosso, Cocalinho, Corixão do Meio (trib. to rio Cristalino; rio Araguaia drainage), approx. 12 km NW of Cocalinho, at road MT-326 (14°11′14″S, 51°14′58″W),col., MZUSP team, 14 Oct 2004; MZUSP 105899, 1 ex, 13.0 mm SL, from MZUSP 86271.
Diagnosis: Distinguished form all congeners except Pc. ahriman, Pc. capeta, and Pc. irritans by the presence of five median premaxillary teeth (some of which often in replacement) (vs. either three or 9 to19 in total). The species is further distinguished from all congeners, except Pc. ahriman and Pc. irritans, by the broad and long ventral portion of the opercular periodontodal fold, forming a lateral ridge of integument extending anteriorly to the dorsal margin of the interopercular odontodophore (vs. ventral part of fold not anteriorly extended, independent from interopercular odontodophore). Distinguished from Pc. ahriman by the longer caudal peduncle (21.8-24.0% SL, vs. 19.2-21.5); by the shorter predorsal length (66.7-71.3% SL; vs. 71.8-76.7); by the narrower anterior internarial width (13.3-17.1% HL; vs. 17.6-20.2); by the narrowersmaller posterior internarial width (8.1-10.0% HL; vs. 10.1-11.4). Distinguished from Pc. capeta by the longer caudal peduncle (21.8-24.0% SL; vs. 18.0-20.4); by the deeper caudal peduncle (10.8-13.0% SL; vs. 7.0-8.8); by the longer predorsal and preanal lengths (66.7-71.3 and 68.6-70.3% SL; vs. 72.2-74.1 and 71.8-75.9, respectively); by the wider head (75.7-83.3% SL; vs. 68.0-72.0); by the smaller eye (14.7-16.2% SL; vs. 16.7-21.7); by the mouth cleft directed more strongly posteriorly than laterally (vs. opposite); by the roundish median premaxilla (vs. trapezoidal with nearly straight anterior margin). Distinguished from Pc. irritans by having 5 + 5 principal caudal-fin rays (vs. 6 + 6); by the deeper caudal peduncle (10.8-13.0% SL; vs. 8.3-10.6); by the wider posterior internarial width (8.1-10.0% HL; vs. 3.3-5.5); by more numerous procurrent caudal-fin rays (28-30 dorsally and 27-29 ventrally, vs. 19-25 dorsally and 21-25 ventrally); by the deepest portion of the caudal peduncle (corresponding to longest procurrent caudal-fin rays) approximately at its halflength (vs. caudal peduncle progressively deeper to base of caudal fin); by the dorsal and ventral profiles of caudal peduncle posteriorly strongly converging towards base of caudal fin, forming pronounced concave regions clearly delimiting beginning of caudal fin (vs. dorsal and ventral profiles of caudal peduncle gently continuous with caudal fin, with only slight depression in some specimens); by the interorbital larger than eye diameter (vs. smaller).
Description: Morphometric data for the holotype and paratypes are provided in Table 3. Body moderately elongate (HL 16.7-18.0% SL). Cross-section of body slightly broader than deep at pectoral-fin insertion and increasingly compressed posterior to that point, tapering to caudal fin. Dorsal profile of body gently convex, nearly straight, from head to origin of dorsal fin (Fig. 11). Dorsal and ventral profiles of caudal peduncle strongly convex posterior to ends of dorsal and anal fins, spatulate, expanded by procurrent caudal-fin rays (Fig. 11). Dorsal and ventral profiles of caudal peduncle strongly converging towards base of caudal fin, forming pronounced concave regions clearly delimiting beginning of caudal fin. Ventral profile of body straight to pectoral-fin base and then gently convex until pelvic-fin origin, with some specimens with distented abdomens due to gut contents.Myotomes and longitudinal skeletogenous septum clearly visible through thin integument along whole body. In few specimens, axillary gland full with secretion, very large and protruding markedly on surface of body. In majority of specimens, gland empty, much smaller and less conspicuous. When full, anterior end of gland surrounding dorsoposterior, ventral and posterior margins of muscular pectoral-fin base, as thick corselet, extending posteriorly beyond margin of adpressed pectoral fin for distance equivalent to fin length. Gland narrowing to blunt posterior end, extending along limit between hypaxial musculature and abdominal cavity, its large round or oval pore located at middle of pectoral-fin length or slightly anterior to that, in dorsal view. Condition of gland posterior to pore evidently related to amount of secretion stored at time of preservation.
Dorsal profile of head continuous with that of dorsum (Fig. 11), its origin indicated by slight constriction of anterior end of epaxial musculature. Head longer than broad (head width 75.7-83.3% HL), snout broad, parabolic with a continuous round anterior margin. Head muscles not entering skull roof. Head moderately depressed (head depth 33.3-41.7% HL) with dorsal profile gently convex, nearly straight, with curvature accentuated close to tip of snout. Ventral profile of head straight, flat. Eye small (14.7-16.2% HL), without free orbital rim, located dorsolaterally on head and directed dorsolaterally, with pronounced lateral component (Fig. 11). Integument over eye thin and transparent. Middle of eye slightly anterior to middle of HL. Interorbital larger than eye diameter.Eyelens unconstricted by iris in specimens examined. Anterior nostril small, surrounded by short tubule of integument produced posteriorly into well-defined pointed nasal barbel, with double elastin cores. Anterior internarial width approximately equal to interorbital. Posterior naris as large as anterior one, adjacent to anteromesial margin of eye and partly occluded by anterior flap of integument. Anterior margin of posterior naris leveled or slightly anterior to transverse line through anterior margin of eyes. Posterior internarial width narrower than interorbital and larger than diameter of one nostril.
Opercular odontodophore well exposed on dorsolateral surface of head, on dorsal half of head depth in lateral view, anterodorsally to pectoral-fin base. Opercular odontodes 6 to 9, closely positioned in more or less irregular roundish disposition, with two largest ones posteriorly. Main axis of opercular odontodes oriented horizontally in lateral view, with distal portions of larger posterior ones curved dorsoposteriorly. Opercular periodontodal fold well-differentiated but short, extending shortly beyond tips of odontodes, its ventral side extending anteriorly as broad straight or slightly convex ridge to dorsal margin of interopercular periodontodal fold. Interopercular odontodophore slightly smaller than opercular one, located ventrolaterally on head, immediately ventral to horizontal through origin of pectoral fin, with 8 or 9 odontodes closely positioned in two irregular, partly imbricating, rows. Interopercular odontodes larger posteriorly, dorsal ones curved dorsoposteriorly and ventral ones curved ventroposteriorly. Interopercular odontodophore slightly closer to opercular one than to eye. Interopercular periodontodal fold of integument well-developed, roundish, extending well beyond tips of odontodes. Epiodontodeal velum thin and transparent, covering most of odontodes.
Mouth inferior (ventral). Each premaxilla with 1 or 2 scalpelloid teeth attached (in parallel when 2) to its distal tip (Figs. 4C, 12). Two tooth sockets always present, but one of them usually in process of replacement. Scalpelloid teeth deeply hidden in labial tissue and impossible to expose in preserved specimens without damaging soft tissue. No conical teeth on premaxilla. Upper lip very broad, continuous with ventral surface of snout (Fig. 11). Median premaxilla small, restricted to middle of upper jaw, with 5 teeth closely disposed in one row, with central tooth largest and two smaller ones on each side (Figs.4C, 12). In most specimens, one or two teeth in process of replacement, but total count of five obvious by tooth sockets and relative position of attached teeth. Tooth bases disposed at approximately same transverse line, with lateral-most teeth slightly anterior to others. All teeth posteriorly oblique to ventral surface of median premaxilla at base and curved further posteriorly at distal pungent portion. Basal portion of all median premaxillary teeth strongly compressed laterally. Median premaxillary velum well-defined, semicircular, covering whole dentition when intact. Hypodontal pad of median premaxilla small, forming round mound following tooth distribution. Lower jaw narrow, composed mostly of short pointed dentary lobes, mostly confluent at midline, continuous with mental region posteriorly (Fig. 11). Jaw cleft short, oblique relative to longitudinal axis. Dentary diastema small and angulate. Dentary teeth 4 (when 3, replacement one in formation), closely packed at mesial end of dentary and disposed as two ventral and two dorsal ones, not exactly aligned (Figs. 4C, 12). Dentary teeth long and strongly curved, with ventral ones longer and with curvature positioned distally and dorsal ones shorter and with curvature approximately at midlength. All dentary teeth with their axis anteromesially-directed at base, but strongly curved dorsally at distally.
Branchiostegal velum forming large free fold, in continuous posteriorly concave arc across whole of mental region (Fig. 11). Dorsal portion of fold reaching, but not covering, anterior margin of pectoral-fin base. Branchial openings small, spanning part of area between ventral margin of opercular odontodophore and mid-depth of interopercular odontodophore,anteroventrally to pectoral-fin base. Maxillary barbel very thin, especially distally, reaching to midlength of interopercular odontodophore. Posterior point of its base at, or slightly anterior to, vertical through anterior margin of eye in lateral view. Mesial (or ventral) part of maxillary-barbel base inserting directly onto corner of mouth without intervening membranous outgrowth. Rictal barbel small to vestigial, attached mesially to base of maxillary. Nasal barbel small but well differentiated, continuous with posterior portion of integument fold around anterior naris described above, with double internal elastin core visible in cleared and stained specimens.
Lateral line very short, slightly curved dorsally distally, extending alongside dorsal margin of anterior portion of axillary gland. Terminal lateral-line pore dorsal to axillary gland opening. Very short secondary branch splitting off ventrally from proximal portion of main canal, with corresponding pore opening at approximately basal third of main canal. Single lateral-line tubule very poorly calcified, extending for most of main canal posterior to bifurcation.
Pectoral fin short (62.5-70.0% HL), with convex-truncate margin, its base on ventral side of body. Pectoral-fin rays i + 5 (i + 6 on one side of one specimen). Pelvic fin very small, close to each other at base, modally with i + 4 rays, (a few specimens with i + 3 or i + 5), with variable branching pattern ranging from all rays unbranched to maximum of four branched. Pelvic splint present. Origin of pelvics close to origin of anal fin, slightly anterior to vertical through origin of dorsal-fin, entirely covering anus and urogenital papilla and extending posteriorly to origin of anal fin. Posterior margin of pelvic fin round. Dorsal fin roughly rectangular-roundish,with gently convex distal margin. Dorsal-fin rays ii + 5 plus 3 or 4 procurrent ones. Anal fin similar in size and shape to dorsal fin but more roundish, modally with ii + 5 rays, plus 4 or 5 procurrent ones. Origin of anal fin at vertical through origin of dorsal fin. Caudal fin truncate with round corners, less deep than maximum depth of caudal peduncle. Principal caudal-fin rays 5 + 5. Procurrent caudal-fin rays 28 (n = 2), 29 (n = 3) or 30 (n = 1) dorsally and 27 (n = 2), 28 (n = 2) or 29 (n = 2) ventrally.
Vertebrae 42 (n = 1), 43 (n = 2) or 44 (n = 3). First dorsal-fin pterygiophore subsequent to neural spine of vertebra 21 (n = 3) or 22 (n = 3). First anal-fin pterygiophore subsequent to haemal spine of vertebra 21 (n = 1), 22 (n = 2) or 23 (n = 3). Dorsal-fin pterygiophores 6 (n = 1) or 7 (n = 5). Anal-fin pterygiophores 6 (n = 6). Branchiostegal rays 3.
Pigmentation in preservative: Body almost entirely white. Faint series of irregular dark spots along dorsal midline to origin of dorsal fin, bilaterally arranged in few specimens. Posterior part of caudal peduncle with irregular longitudinal stripe formed by internal chromatophores along vertebral column, with some dark spots also over hypural plate in some specimens. Dorsal half of abdomen with isolated dark chromatophores, especially visible in specimens with distended abdomens. Posterior half of neurocranium with irregular dark brain pigment seen by transparency, forming anteriorly concave rough pattern, extending anteriorly along edges of neurocranium as two lines sometimes extending as series of spots between eyes and nostrils and along mesethmoid. Intense irregular dark fields anteriorly to eyes, also extending ventrolaterally towards maxillary barbel base. Some specimens with few isolated chromatophores at base of opercular odontodophore. Internal pigmentation intense, with nearly entire vertebral column covered with dark chromatophores, especially concentrated on bases of neural spines of trunk. Internal chromatophores also on dorsal surface of peritoneum and lateral surface of cardiac region.
Geographical distribution: Known so far from the rio Araguaia basin (Fig. 20).
description: Published as part of Pinna, Mário de & Dagosta, Fernando Cesar Paiva, 2022, A taxonomic review of the vampire catfish genus Paracanthopoma Giltay, 1935 (Siluriformes, Trichomycteridae), with descriptions of nine new species and a revised diagnosis of the genus, pp. 1-90 in Papéis Avulsos de Zoologia 62 on pages 21-25, DOI: 10.11606/1807-0205/2022.62.072, http://zenodo.org/record/7617440