Paracanthopoma ahriman Pinna & Dagosta 2022, new species
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 ahriman

description: Paracanthopoma ahriman, new species
(Fig. 5)
Holotype: FMNH 105525, 19.9 mm SL, Venezuela, T.F. Amazonas, río Autana at Playa Cucurito in front of caño Cucurito (approx. 05°14′N, 66°10′W), col., B. Chernoff, A. Machado & J. Wheeler, 09 Feb 1992.
Paratypes: All collected with holotype. FMNH 147290, 10 ex (2 c&s, 1 SEM), 17.5-20.4 mm SL; MZUSP 126890, 3 ex (1 c&s), 17.2-19.6 mm SL.
Non-type specimens: MHNLS 18018, 8 ex, 15.0- 17.4 mm SL, Venezuela, Amazonas, Caño Guachapana (trib. to Río Orinoco) (03°21′17,6″N, 69°02′25,0″W), col., C. Lasso, O. Lasso-Alcala, O. Leon Mata, D. Rodriguez Olarte, 28 Nov 2003; MHNLS 24334, 1 ex, 21.82 mm SL, Colombia, Vichada, Rio Guaviare (Río Orinoco drainage), Laguna El Gusano, margen derecha (03°57′36,6″N, 67°57′56,6″W), col., C. Lasso, M. Sierra, M. Patiño, F.Villa, A. Ortega, 16 Feb 2008.
Diagnosis: Unique among Paracanthopoma in having 45 vertebrae (vs. 44 or fewer). Distinguished form all congeners except Pc. cangussu, Pc. capeta, and Pc. irritans by the presence of five median premaxillary teeth (with one or two often in replacement) (vs. either three or 9 to19 in total). The species is further distinguished from all congeners, except Pc. cangussu and Pc. irritans, by the broad and horizontally 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.cangussu by the shorter caudal peduncle (19.2-21.5% SL,vs.21.8-24.0), by the longer predorsal length (71.8-76.7% SL;vs. 66.7-71.3); by the wider anterior internarial width (17.6-20.2% HL; vs. 13.3-17.1); by the wider posterior internarial width (10.1-11.4% HL; vs. 8.1-10.0). Distinguished from Pc. capeta by the broader head (head width 80.7-87.6% HL; vs. 68.0-72.0); 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 the broader head (head width 80.7-87.6% HL; vs. 73.3-76.9); by the broader interorbital (14.8-17.9% HL; vs. 11.0-12.8); by the wider anterior internarial width (17.6-20.2% HL; vs. 13.4-16.5); by the larger posterior internarial width (10.1-11.4% HL; vs. 3.3-5.5). The heavy dark pigmentation of the head, forming striking contrast with its mostly white body, distinguishes Pc.ahriman from all other vandelliines. The peculiar dark pattern is composed of brain pigment, seen by transparency, in combination with integumentary chromatophores disposed in specific areas. Brain pigment covers the posterior part of the neurocranium, extending anteriorly alongside lateral margins of skull as narrow dark fields. Integumentary pigment covers the opercular odontodophore and region immediately surrounding it, with a dark band extending along the ventral margin of opercular odontodophore anteriorly to alongside dorsal margin of interopercular odontodophore, and slightly beyond.The intensity of such dark cephalic pigmentation is unique to the species, but is now faded in available specimens, so it can only be useful for identification in freshly-preserved specimens.
Description: Morphometric data for the holotype and paratypes are provided in Table 1. Body relatively short (HL 17.0-18.3%SL). Cross-section of body depressed at pectoral-fin insertion, becoming round at approximately midlength of pectoral fin, and increasingly compressed posterior to that point. Caudal peduncle tapering gradually to caudal fin as seen in dorsal view. Dorsal profile of body gently convex from head to origin of dorsal fin (Fig. 5), with translucent middorsal keel along posterior two-thirds of that trajectory. Dorsal profile of head continuous with that of dorsum, anterior portion of which flattened.Caudal peduncle paddle-shaped,its dorsal and ventral profiles convex, strongly expanded immediately posterior to tips of dorsal and anal fins, due to well-developed procurrent caudal-fin ray series (Fig. 5). Ventral profile of body and head straight until tip of pectoral fin, then gently convex or straight to origin of pelvic fin. Ventral profile of body posterior to anus straight to region of ventral accessory caudal-fin rays. Myotomes visible along whole body, progressively narrower and more sloped posteriorly. Region of longitudinal skeletogenous septum visible along nearly whole body. Integument thin, not heavily covering bases of fins. Axillary gland large, involving most of pectoral-fin base, except anteriorly, and extending posteriory to beyond limit of pectoral fin for variable distance, maximally for distance equivalent to fin length. Gland tapering posteriorly, with its posterior part more or less visible according to volume of secretion in lumen at time of fixation. Axillary gland pore hypertrophied, located at vertical through midlength of pectoral fin, directed dorsoposteriorly and widely open in most specimens.
Dorsal profile of head continuous with that of dorsum (Fig. 5). Head longer than broad, (head width 80.7-87.6% HL) snout round and broad, slightly differentiated from rest of head (Fig. 5). Muscles not significantly covering dorsal part of head, neurocranium entirely exposed. Head depressed, its depth 34.0-45.9% HL, with dorsal profile straight and horizontal in lateral view until anterior nostrils,then angled ventrally and straight to tip. Eye large, (15.0-17.6% HL) without free orbital rim, located dorsolaterally on head and directed anterodorsolaterally. Integument over eye thin, whole eyeball visible in preserved specimens. Eyes mostly on anterior half of HL, interorbital width approximately equal to longitudinal diameter of eye. Eyelens occupying much of lateral surface of eye and constricted by round iris only marginally. Anterior nostril small (Fig. 6), located in small depression of integument and surrounded by short tubule of integument produced posteriorly into small round or slightly pointed process, with double elastin cores. Anterior internarial width equal or slightly larger than interorbital. Posterior naris roundish and slightly smaller than anterior ones, with short flap of integument anteriorly, not occluding opening (Fig. 6). Posterior naris positioned mesially to eye, their anterior margin posterior to transverse line through anterior margin of eyes. Posterior internarial width narrower than interorbital.
Opercular odontodophore large, larger than eye when periodontodal fold included, dorsolaterally located on head, at middepth of head in lateral aspect (Fig. 5). Periodontodal fold very large, especially ventrally, encircling dorsal, posterior and ventral sides of odontodophore and maximally over 50% of depth of toothed portion. Ventral portion of periodontodal fold extending anteriorly as broad straight or slightly convex ridge to dorsal margin of interopercular periodontodal fold, forming horizontal keel between two odontodophores. Opercular odontodes 6, closely positioned in roughly circular arrangement, with three smaller anterior and three posterior larger ones. Main axis of opercular odontodes oriented horizontally in lateral view, with distal portions of larger posterior ones curved strongly mesially (with top and bottom odontodes of that series with some dorsal and ventral components, respectively). Curvature less intense in smaller three odontodes of anterior series.Few caps of replacement odontodes interspersed with mature ones. Interopercular odontodophore similar in size to opercular one, located ventrolaterally on head, immediately ventral to horizontal through origin of pectoral fin, with 7 odontodes closely positioned in two irregular rows, with larger ones in posterior row. Interopercular odontodophore closer to opercular one than to eye.Two or three replacement tooth caps located posteromesially to mature ones. Interopercular periodontodal fold of integument well-developed, oval and extending well-beyond tips of odontodes, especially posterolaterally. Epiodontodeal velum thin and transparent,covering more than half of length of odontodes.
Mouth inferior (ventral), strongly flattented (Fig. 5). Each premaxilla with single scalpelloid teeth attached to its distal tip (visible only in skeletal preparations; Figs. 4A, 7), but actually two adjacent tooth sockets, one of which normally vacant, corresponding to half-formed replacement tooth adjacent to mature one. Three additional initial-stage replacement caps suspended in soft tissue directly dorsal to mature one and its incomplete neighbor. Mature scalpelloid tooth with distal portion disproportionately reduced and very strongly curved over rest of teeth, with tiny pungent tip nearly adpressed to margin of basal plate. Scalpelloid tooth deeply hidden in labial tissue and impossible to expose in preserved specimens without damaging soft tissue. Conical teeth absent in premaxilla (Figs. 4A, 7). Paralabial sac apparently reduced to space immediately mesial to distal portion of premaxilla, entirely inside of mouth and difficult to locate externally. Upper lip very thick, obliterating much of mouth opening. Median premaxilla small, with 5 teeth disposed in single row, with one central largest tooth and two smaller ones on each side (Figs. 4A, 7). 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 median tooth slightly more anterior. All teeth posteriorly oblique to ventral surface of median premaxilla at base, at approximately 45° angle, and curved further posteriorly at distal pungent portion. All median premaxillary teeth strongly laterally compressed basally, with the central one extremely broad longitudinally- and flat-based.Three to five replacement tooth caps posterodorsally to mature dentition. Median premaxillary velum thick, covering all teeth when extended. Hypodontal pad of median premaxilla narrow, following profile of median premaxilla. Lower jaw narrow, composed mostly of narrow and pointed, triangular dentary lobes, continuous with mental region posteriorly (Figs. 5, 6). Jaw cleft short and strongly directed laterally, its lateral portion almost transverse to longitudinal axis and leaving little or no space separating lower jaw from inner margin of upper jaw. Dentary diastema small, strongly concavely or angulate, fitting snugly onto posterior margin of median premaxilla. Rami of mandible very close together at midline. Dentary teeth 3 or 4, closely packed at mesial end of dentary and disposed as two ventral teeth and one or two dorsal ones (Figs.4A, 7). Axis of dentary teeth anteromesially-directed at base, but curved anterolaterally at distal third. Branchiostegal velum forming large, continuous, round and posteriorly concave curve across whole of mental region.Dorsal portion of branchial membrane approaching but not covering anterior margin of pectoral-fin base. Branchial openings small,spanning approximately area between ventral margin of opercular odontodophore and dorsal margin of interopercular periodontodeal fold. Maxillary barbel very short and proximally broad, its base flap-like, only distal portion filamentous (Figs. 5 and 6). Posterior point of its base at, or slightly anterior to, vertical through anterior margin of eye, its tip extending posteriorly maximally to base of interopercular odontodes, but often shorter than that. Mesial (or ventral) part of maxillary-barbel base inserting directly onto corner of mouth without major intervening membranous outgrowth. Rictal barbel (Fig. 6) located mesially to base of maxillary one and varying in size (sometimes between sides of specimen), ranging from nearly absent externally to approximately one-fifth of maxillary barbel length. Nasal barbel vestigially represented by posterior elongated portion of fold around anterior naris described above, with double internal elastin core.
Lateral line short and mostly straight, surrounded by thickened tissue similar to that of axillary gland, making its profile extremely thick on surface of body. Terminal lateral-line pore approximately at vertical through midlength of pectoral-fin, near dorsal margin of axillary pore, slightly produced laterally from surface of body. Short secondary branch splitting off ventrally from anterior portion of canal, with corresponding pore opening approximately at midlength of main canal. Single short lateral-line tubule curved and irregularly calcified, extending approximately for middle one-third of main canal.
Pectoral fin short (69.2-78.4% HL), with i + 5 rays,truncate or gently convex, its distal margin irregular at close range, its base on ventral side of body. Pelvic fins small, well-separated from each other at base, with i + 4 rays. Pelvic splint present. Origin of pelvics well anterior to vertical through origin of dorsal-fin, entirely covering anus and extending posteriorly well beyond origin of anal fin. Posterior margin of pelvic fin round. Dorsal fin small, with approximately same area as caudal fin in lateral aspect, broadly triangular with round apex or roughly rectangular, with gently convex distal margin and ii + 5 (only one specimen) or ii + 6 fin rays, plus 5 procurrent ones. Anal fin small, approximately with same size as dorsal fin and slightly more elongate and rectangular in shape than latter,with gently convex distal margin and ii +5 fin rays,plus 5 procurrent ones. Origin of anal fin at vertical through origin of dorsal-fin. Anal fin with same size, slightly smaller or slightly larger than dorsal one.Caudal fin truncate with round edges, slightly convex in some specimens, less deep than maximum depth of caudal peduncle. Principal caudal-fin rays 5 + 6, 6 + 6 or 6 + 7 (modally 6 + 6), with variation apparently due mostly to differences in branching patterns. Procurrent caudal-fin rays 26 dorsally and 25 ventrally (values based on one specimen only).
Vertebrae 45 (n = 10). One specimen with 46, but due to one deformed duplicated vertebra. First dorsal-fin pterygiophore subsequent to neural spine of vertebra 23 (n = 3). First anal-fin pterygiophore subsequent to haemal spine of vertebra 23 (n = 2) or 24 (n = 1). Dorsalfin pterygiophores 7 (n = 3). Anal-fin pterygiophores 6 (n = 3). Branchiostegal rays 3 or 4, with number bilaterally asymmetrical in two specimens.
Pigmentation in preservative: Specimens nearly entirely white at present, due to postmortem fading. Description below based on condition prior to fading. Body mostly white. Irregular row of internal dark chromatophores along vertebral column in caudal peduncle, irregularly outlining individual vertebrae. Large dark dots irregularly spaced along dorsal and ventral profiles of caudal peduncle, extending along bases of dorsal and anal fins and sometimes also along dorsum. Series of peritoneal dark chromatophores on dorsal limit of abdominal cavity, near border of hypaxial series, especially pronounced on posterior half of abdomen. Head with intense dark pigmentation (Fig. 3A) contrasting with mostly white body. Main dark field on head formed by brain pigment visible by transparency on posterior part of neurocranium, with two narrow convergent fields extending anteriorly and meeting between eyes. Integumentary pigment covering opercular odontodophore and region immediately surrounding it, with very dark narrow band along ventral margin of opercular periodontodal fold extending anteriorly alongside dorsal margin of interopercular periodontodal fold, and further anteriorly to approximately vertical through middle of eye. Separate irregular dark field anteroventral to eye. Few dark spots on anterior portion of dorsal surface of pectoral-fin base.
Etymology: The name is from Zoroastrian religion, the oldest monotheism, and refers to Angra Mainyu (Ahriman in Persian), enemy of Ahura Mazda, creator of the universe. Ahriman is the maker of snakes, demons and all things evil from a human standpoint (thus, presumably also candirus) and is approximately equivalent to, and probably historical ancestor of, the devil in Abrahamic mythology.
Geographical distribution: Paracanthopoma ahriman, is known from the upper río Orinoco in Venezuela (Fig. 20).
Remarks: This species shows the most constant vertebral number in Paracanthopoma, with 10 examined specimens all with 45 vertebrae.
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 11-16, DOI: 10.11606/1807-0205/2022.62.072, http://zenodo.org/record/7617440