Paracanthopoma truculenta, Pinna & Dagosta, 2022

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, Papéis Avulsos de Zoologia 62, pp. 1-90 : 64-69

Paracanthopoma truculenta , new species ( Fig. 39 )

Paracanthopoma sp. 1 – Wosiacki & de Pinna, 2007: 73 [catalog].

Holotype: MZUSP 30399 , 39.7 mm SL, Rondônia, rio Madeira, Calama (08°01′42″S, 62°52′34″W), col., M. Goulding, Feb-May 1980.

Paratypes: BRAZIL: INPA 8188 , 1 ex, 38.6 mm SL, Amazonas, rio Solimões, downstream from mouth of rio Purus (trawled at 20 m depth),col., C. Cox, J. Lundberg & L. Rapp Py-Daniel, 19 Oct 1992 ; INPA16830 , 1 ex, 41.4mm SL, rio Madeira,col., M. Goulding,no date ; MZUSP 30401 , 6 ex, 35.1-47.1 mm SL, Brazil, Rondônia, rio Madeira at Calama (08°01′42″S, 62°52′34″W),col., M.Goulding, Feb-May 1980 ; MZUSP 30404 , 20 ex (2 c&s), 26.5-40.6 mm SL, Rondônia, rio Madeira at Calama (08°01′42″S, 62°52′34″W), col., M. Goulding, Feb-Apr 1980 ; MZUSP 30409 , 11 ex, 25.6-39.5 mm SL, Rondônia, rio Madeira at Calama (08°01′42″S, 62°52′34″W),col., M.Goulding, Feb-May 1980 ; MZUSP 30422 , 13 ex, 22.3-44.4 mm SL, Rondônia, rio Madeira at Calama (08°01′42″S, 62°52′34″W), col., M. Goulding, Feb-Apr 1980 ; MZUSP 100750 , 7 ex (1 c&s), 25.6-37.4 mm SL, Rondônia, rio Madeira at Calama (08°01′42″S, 62°52′34″W), col., M. Goulding, Feb-Apr 1980 ; MZUSP 103048 , 10 ex, 35.5-50.7 mm, collected with holotype ; PERU: MUSM10849 , 1 ex, 37.5mm SL, Madre de Dios, Tambopata ,río Madre de Dios,col., F.Chang, 16 May 1996 ; MUSM 19977 , 1 ex, 41.0 mm SL, Madre de Dios, Manu , río Madre de Dios, col., M. Goulding et al., 24 Aug 2001 .

Non-type material: BOLIVIA: MZUSP 27854, 3 ex, 28.3-37.8 mm SL, Madre de Dios at Riberalta (rio Madeira drainage), col., joint expedition ORSTON-UTB, 20 May 1983; BRAZIL: MZUSP 30402 , 3 ex, 35.9-41.0 mm SL, Rondônia, rio Madeira at Calama (08°01′42″S, 62°52′34″W), col., M. Goulding, Feb-Apr 1980 ; MZUSP30403 , 1 ex, 33.7mm SL, Amazonas, rio Madeira at Aripuanã [= Novo Aripuanã] (from body of Piraíba, Brachyplatystoma filamentosum , 82 cm), col., M. Goulding, 11 Dec 1980 ; MZUSP 30410 , 1 ex, 35.9 mm SL, rio Madeira, col., M. Goulding, 21 Dec 1979 ;

Diagnosis: Distinguished from all congeners by the very reduced opercular odontodophore, bearing only one or two odontodes not protruding from surface of head, sunk in small slit of integument (vs. opercular odontodes minimally four, clearly visible on surface of skin, even when small). Distinguished from all congeners, except Pc. carrapata , Pc. daemon , and Pc. parva , by the presence of nine (sometimes 10 in Pc. daemon ) teeth on the median premaxilla (vs. 3 to 5 or 11 and more); by the presence of a single median s6 pore, visible on the middle of skull posterior to eyes (vs. paired s6 pores, distant from midline of skull), and by the supraoccipital anteriorly produced into large pointed spike (vs. either anteriorly concave or straight across skull roof). Distinguished from all congeners except Pc. parva and Pc. carrapata by the posterior margin of the anal fin well posterior to vertical through that of the dorsal fin (vs. margins of two fins approximately at same vertical or that of anal fin only slightly posterior to that of dorsal fin); and by the deeply emarginate, bilobed caudal fin (vs. truncate with round corners or only slightly concave). Distinguished from all congeners except Pc. carrapata by the extensive invasion of the skull roof by head musculature, with widest exposed part of neurocranium approximately equivalent to interorbital (vs. exposed part of neurocranium larger than interorbital). Further distinguished from Pc. carrapata by the proportionally smaller eye (9.9-13.3% HL; vs. 13.9-14.4); and the shorter head (16.5-20.0% HL; vs. 20.9-22.2).

Description: Morphometric data for the holotype and paratypes are provided in Table 12 . Body elongate (HL 16.5-20.0% SL). Cross-section of body depressed at pectoral-fin insertion, becoming round along anterior fourth trunk and increasingly compressed posterior to that point, tapering to caudal fin. Dorsal profile of body gently convex from head to origin of dorsal fin ( Fig. 39 ). Dorsal and ventral profiles of caudal peduncle gently convex sometmes slightly angulate at beginning of pro-current caudal-fin rays. Caudal peduncle narrow, but expanded by procurrent rays along posterior third or half. Ventral profile of body slightly swollen at cardiac region, then concave, straight or convex, depending on condition of gut content, until pelvic-fin origin. Myotomes clearly visible along whole body. Longitudinal skeletogenous septum also evident along whole of body, except anterior third of trunk in large individuals. Axillary gland short, posteriorly not reaching margin of adducted pectoral fin, not protruding markedly on surface of body and covering only very base of pectoral fin. Its large pore opening slightly anterior to midlength of pectoral fin.

Dorsal profile of head separated from that of dorsum by pronounced muscle separation. Head longer than broad (head width 55.4-66.1% HL), snout broad, parabolic with a roundish-pointed tip ( Figs. 39 , 40 ). Muscles covering most of dorsal part of head, with head width approximately 4.5 times the width of exposed skull roof in dorsal view. Exposed area proportionall larger in small specimens. Head deep for Paracanthopoma (head depth 20.5-32-0% HL), with convex dorsal profile, strongly curved ventrally anteriorly to eye. Eye small (9.0-13.3% HL), without free orbital rim, located dorsolaterally on head and directed dorsolaterally. Integument over eye thin, entire eyeball visible through skin. Middle of eye slightly anterior to middle of HL, interorbital width approximately 1.5 times longitudinal diameter of eye. Eyelens very large, taking most of lateral surface of eye and either entirely unconstricted by iris or constricted only marginally, with large round pupil, in specimens examined. Anterior nostril small, surrounded by short tubule of integument produced posteriorly into small pointed process ( Figs. 39 , 40 ), with double elastin cores. Anterior internarial width equal or slightly larger than interorbital. Posterior naris slightly larger than anterior ones, round, but usually with semilunar opening because of partial occlusion by anterior flap of integument ( Figs. 39 , 40 ). Posterior naris positioned anteromesially to eye, their middle approximately at transverse line through anterior margin of eyes. Posterior internarial width narrower than interorbital.

Opercular odontodophore tiny, laterally or slightly dorsolaterally located on head, approximately at, or slightly dorsal to, middepth of head ( Figs. 39 , 40 ). Odontodophore externally identifiable mostly by its proportionally small, oval associated periodontodeal fold. Opercular odontodes 1 or 2, closely positioned and not protruding from surface of head and sometimes entirely sunk in integument, their location in these case externally indicated by narrow horizontal slit. Main axis of opercular odontodes oriented horizontally in lateral view, with their distal portion curved dorsally. One or two caps of replacement odontodes posteromesially to mature ones. Interopercular odontodophore tiny ( Figs. 39 , 40 ), located ventrolaterally on head, at horizontal through origin of pectoral fin, with 2 or 3 odontodes closely positioned in single row,much closer to opercular odontodophore than to eye. Two or three replacement tooth caps located posteromesially to mature ones. Interopercular periodontodal fold of integument small, nearly semicircular. Epiodontodeal velum translucent, very small but proportional to size of odontodophore, entirely covering odontodes when extended.

Mouth inferior (ventral), filled in most specimens with tightly bitten chunks of meat, supposedly from host fish, often entirely hiding internal mouth morphology. Mouth very large, occupying most of anterior part of head ventrally ( Figs. 39 , 40 ). Each premaxilla with single scalpelloid teeth attached to its distal tip (visible only in skeletal preparations), but actually two tooth sockets adjacently-positioned,one of which normally vacant,corresponding to half-formed replacement tooth adjacent to mature one ( Figs. 4K , 41 ). Normally one additional initial-stage replacement cap nearby. Mature scalpelloid tooth with distal portion disproportionately reduced and very strongly curved over rest of teeth, with pungent tip nearly adpressed to margin of basal plate. Scalpeloid teeth deeply hidden in labial tissue, its distal surface barely rupturing surface even when premaxilla forcibly abducted. Conical teeth absent in premaxilla. Upper lip thick, deeply plicate on parabucal surface. Median premaxilla very large, with 9 teeth disposed in one anterior row of four (anteriorly convex), one posterior row of four (convex posteriorly), plus single middle tooth ( Figs. 4K , 41 ). Teeth on anterior row more or less evenly spaced, those on posterior row more widely spaced medially than laterally. All nine teeth perpendicular to median premaxilla at base, but strongly curved posteriorly at distal pungent portion, those of anterior row taller than those of posterior row. All median premaxillary teeth strongly laterally compressed basally. Numerous replacement tooth caps posterodorsally to mature dentition, creating crowded aspect at posterior limit of median premaxillary dentition. Median premaxillary dentition occupying almost all of upper jaw and most of interior of mouth. Median premaxillary velum absent. Hypodontal pad of median premaxilla thickly cushioning teeth. Lower jaw wide, with long dentary lobes nearly entirely fused to each other at midline, continuous with mental region posteriorly. Lower jaw cleft deep and strongly directed posteriorly, approaching parallel to longitudinal axis and with broad space separating it laterally from inner margin of upper jaw. Dentary diastema poorly differentiated, represented by small concave, sometimes angulate area at midline, entirely absent in some specimens. Rami of mandible very close together at midline. Dentary teeth 4 or 5 (normally 4), closely packed at mesial end of dentary ( Figs. 4K , 41 ). When 4, teeth disposed in two pairs, one dorsal and one ventral, with only latter visible in ventral view. When five, ventral row with three and inner row with two teeth. Axis of dentary teeth anteriorly-directed at base, with distal portions curved dorsally or dorsolaterally. Branchiostegal velum forming large, continuous, round and posteriorly concave, free fold across whole of mental region ( Fig. 40 ). Dorsal portion of branchial membrane partly covering anterior margin of pectoral-fin base. Branchial openings small, located anterodorsally to pectoral-fin base, spanning approximately for area between ventral margin of opercular odontodophore and ventral margin of interopercular odontodophore. Maxillary barbel very short and broad, its dorsal margin expanded into membranous keel, progressively larger proximally, only distal portion filamentous. Posterior point of is base anterior to vertical through anterior margin of eye in lateral view, its tip extending posteriorly approximately to vertical through middle of eyes in lateral view. Mesial (or ventral) part of maxillary-barbel base adjacent to membranous outgrowth extending posteriorly from corner of mouth. Rictal barbel small, located mesially to base of maxillary one and approximately half of its size, its base immersed in membranous expansion at corner of mouth, with well-defined membranous lobule mesially ( Fig. 40 ). Rictal barbel sometimes difficult to identify among irregularities of surrounding integument flap, but homology with trichomycterid rictal barbel evident by well-developed internal core. Nasal barbel vestigially represented by posterior elongated portion of fold around anterior naris described above, with double internal elastin core.

Lateral line short, straight along anterior half and bent dorsally at midlength, at approximately 30° to 45°. Its terminal pore approximately at vertical through midlength of pectoral-fin, at horizontal through eye in lateral view, at or slightly posterior to vertical through posterior margin of axillary pore. Short secondary branch splitting off ventrally from anterior portion of canal, with corresponding pore opening approximately at midlength of main canal or slighly anterior to that point. Single lateral-line tubule extending for section of canal between bifurcation and dorsal bending.

Pectoral fin very short, aproximately 50% of HL or less, with i + 4 or i + 5 rays (modally i + 5; one abnormal specimen in MZUSP 30422 with i + 1 rays on left side), first one (unbranched) slightly longer than others in some specimens. Distal margin of pectoral fin gently convex, its base near ventral margin of body in lateral view, when abdomen not distended by gut contents. Pelvic fins small, well-separated from each other at base, with i + 4 rays. Pelvic splint present. Origin of pelvics located anteriorly to vertical through origin of dorsal-fin, covering anus and extending posteriorly to almost reach origin of anal fin. Posterior margin of pelvic fin round. Dorsal fin small, broadly triangular with roundish apex,with gently convex distal margin and ii + 6 fin rays,plus 4 or 5 procurrent ones. Anal fin small,slightly more elongate than dorsal one,with gently convex distal margin and ii + 5 fin rays, plus 4 or 5 procurrent ones.Origin of anal fin slightly posterior to vertical through middle of dorsal-fin base. Anal fin normally smaller than dorsal one, but opposite in some specimens. Caudal fin emarginate, with concavity more pronounced with growth. Principal caudal-fin rays 6 + 7. Procurrent caudal-fin rays 14 or 15 dorsally and 16 or 17 ventrally.

Vertebrae 37 (n = 2), 38 (n = 2), 39 (n = 8) or 40 (n = 14). First dorsal-fin pterygiophore subsequent to neural spine of vertebra 22 (n = 2) or 23 (n = 1). First anal-fin pterygiophore subsequent to haemal spine of vertebra 24 (n = 2) or 25 (n = 1). Dorsal-fin pterygiophores 7 (n = 2). Anal-fin pterygiophores 6 (n = 2). Branchiostegal rays 3 (n = 2).

Pigmentation in preservative: Body almost entirely white. Middorsal region of head, corresponding to narrow neurocranium, dark with brain pigment seen by transparency. Dark field anteriorly to lateral margin of eyes, extending anterolaterally to region immediately dorsal to base of maxillary barbel.Distal magin of hypural plate with narrow dark line, followed shortly posteriorly by similar but slightly wider and more irregular dark field crossing bases of principal caudal-fin rays,sometimes extending shortly horizontally along proximal portions of middle rays.

Etymology: From the Latin truculentus, meaning harsh, cruel, brutish; an allusion to the size of this species, the largest of all Paracanthopoma .

Geographical distribution: Paracanthopoma truculenta occurs primarily in the rio Madeira, along nearly its entire course, through upland and lowland sectors in Bolivia, Brazil and Peru ( Fig. 45 ). A single record exists in the rio Solimões, this being the only record of any Paracanthopoma species in the main channel of the Amazon.

Biology: Surprisingly few specimens of Paracanthopoma truculenta have obvious remains of blood in their gut, with only one or two specimens in few lots with abdomens distended with dark coagulated blood. On the other hand,most individuals (including those distended with blood) have remains of flesh tightly held in their jaws. It seems possible that they attach to the surface of the body of their hosts by a tight bite, so firm that the removal by collectors result in tearing and removal of part of the bitten tissue. That, plus the fact that so few specimens have blood in their guts, raises the possibility that Pc. truculenta feeds partly from blood and other fluids taken directly from the superficial tissues of their hosts, with only occasional visits to the gill chamber for a large intake of blood. Or perhaps even that the occasional blood found comes from superficial sources as well, when the bitten spot happens to be particularly well-vascularized. The mouth morphology of Pc. truculenta is markedly sucker-shaped, more so than in other vandelliines, and it is possible that it can actually exert negative pressure sufficient to extract blood from systemic vascularization, and not only from major vessels.Whichever the case may be, there are indications that Pc. truculenta has rather especial feedings habits among vandelliines and that further study may reveal most interesting trophic adaptations in that species. Paracanthopoma truculenta was collected sympatrically with Pc. carrapata (lots MZUSP 30402 and 30404 of former and 100145 and 100143 of latter).

Remarks: Paracanthopoms truculenta is the largest species as yet known in its genus (max. 50.7 mm SL, MZUSP 103048). However, indirect evidence suggests that the species probably reaches even larger sizes. Cleared and stained large specimens show extensive cartilaginous areas in their skeleton, typical of young bony fishes.The contact area between pterotic, sphenotic and supraoccipital has a wide cartilaginous component very evident in dorsal view. Anteriorly in the skull, the median region between lateral ethmoids and posteriorly between that and the orbitosphenoids is largely cartilaginous. The entire ethmoid cartilage is still large. Finally, the anterior ceratohyal has a band of cartilage near its anterior end which is typical of long bones still undergoing linear growth. All that indicates that Pc. truculenta may reach a size larger still than that of the largest individuals so far captured. Why such specimens have not yet been captured, despite a relative abundance of halfgrown individuals, remains to be discovered.

Figures

Figure 4. Comparative chart of jaws and anterior portion of head of Paracanthopoma species, cleared and stained specimens, ventral views: (A) Pc. ahriman FMNH 105525;(B)Pc.alleynei MZUSP 103052;(C) Pc.cangussu MZUSP 86250;(D)Pc.capeta MZUSP 29154;(E) Pc.daemon MZUSP 95597;(F)Pc.irritans INPA 20529; (G) Pc.malevola MCP 36217;(H) Pc.parva MZUSP 30400;(I) Pc.saci MZUSP 125626; (J) Pc.satanica MZUSP 100149;(K) Pc.truculenta MZUSP 30404;(L) Pc.vampyra MZUSP 100138. Scale bars = 500 μm. Pc.carrapata not shown.

Figure 39. Paracanthopoma truculenta, holotype, MZUSP 30399, 39.7 mm SL.Brazil, Rondônia,Rio Madeira, Calama.(A) Lateral view of body; (B) Dorsal view of head;(C) ventral view of head.

Figure 40. Paracanthopomatruculenta, paratype,MZUSP 30404,SEM images of head.(A) Lateral;(B) Dorsal;(C) Ventral.Scale bar = 500 μm.

Figure 41. Paracanthopoma truculenta, holotype,MZUSP_30399,CT scan images of head skeleton,(A) Lateral;(B) Dorsal;(C) Ventral.

Figure 45. Map of northern South America showing geographical distribution of Paracanthopoma saci (square); Pc. satanica (5-tip star); Pc.truculenta (dot); and Pc. vampyra (10-tip star). Open symbols represent type localities. Some symbols may represent more than a single locality or lot of specimens.