Hoplomyzon cardosoi

Carvalho, Tiago P., Reis, Roberto E. & Friel, John P., 2017, A new species of Hoplomyzon (Siluriformes: Aspredinidae) from Maracaibo Basin, Venezuela: osteological description using high-resolution computed microtomography of a miniature species, Neotropical Ichthyology 15 (1), No. e 160143, pp. 1-16 : 2-12

Hoplomyzon cardosoi

urn:lsid:zoobank.org:act:8331CD18-B92C-4F13-A403-CB9718586E3F

Figs. 1-11

Holotype. MCNG 375 , 18.5 mm SL, Venezuela, Zulia, Colon, Caño La Raya tributary to Río Escalante , Hacienda San Jose , approx. 08°50′N 71°45′W, 8 Sep 1977, D. Taphorn and others.

Paratypes. MCNG 11560 , 1 , 15.7 mm SL, Venezuela, Zulia, Río Ariquaisa [Aricuaisa] bridge via Machiches , approx. 09°24′N 72°36′W, 14 Mar 1981, D. Taphorn . MCNG 26955 , 1 , 15.1 mm SL, Venezuela, Zulia, Río Santa Ana , approx. 09°23′N 72°36′W, 10 Dec 1982, F. Mago Leccia .

Diagnosis. Hoplomyzon cardosoi is distinguished from all congeners by the straight anterior margin of the mesethmoid (vs. with medial notch); a smooth and straight ventral surface of the premaxilla (vs. presence of bony humps on the ventral surface of premaxilla); absence of teeth on dentary (vs. teeth present on dentary); vertebrae anterior to anal-fin pterygiophore with simple ventral processes (vs. bifurcated processes); presence of several filamentous barbel-like structures on the ventral surface of head (vs. small papillous structures on the ventral surface of head); and anal-fin rays 8 (vs. 6 or 7). Additionally, Hoplomyzon cardosoi differs from remaining congeners by the following morphometric features: greater cleithral width 29.8-33.5% SL, mean 31.1 (vs. 23.5-28.7% SL); shorter scapulocoracoid process 3.2-3.8% SL, mean: 3.4 (vs. 5.9-6.9% SL); longer cleithral process 14.1-20.5% SL, mean 16.4 (vs. 9.6-13.4% SL); narrower interorbital width 26.8-27.5% HL, mean 27.1 (vs. 28.6-36.4% HL); lesser distance between anterior nares 14.6-20.0% HL, mean 17.8 (vs. 25.0-28.6% HL); and lesser distance between posterior nares 22.0-29.2% HL, mean: 25.4 (vs. 31.7-36.8% HL).

Description. Morphometric data summarized in Tab. 1. Head and body depressed. Dorsal profile rising gently from snout tip to dorsal-fin origin with several small humps in between, then descending gradually to end of caudal peduncle; ventral profile straight to slightly convex from mouth to anus, ascending gradually from this point to end of anal fin, almost straight from this point to posterior end of caudal peduncle. Rostrum rounded in dorsal view, lacking medial mesethmoid notch. Head broad, body broadest at pectoral-fin insertion. Caudal peduncle long and slender, squarish in cross section ( Figs. 1-2).

Anterior nares located dorsally about midway between snout tip and posterior nares, enclosed by fleshy tube; anterior margin of tube with small flap-like papillae. Posterior nares lacking fleshy tube, aligned with lateral margin of eye. Rostrum overhanging ventrally displaced mouth; gape small. Upper lip with pair of lateral main papillae and median unpaired one, additional small papillae displaced anterior to these ones.

Three main pairs of barbels, all simple. Maxillary barbel short, almost reaching pectoral-fin origin. Three rictal barbels within ventral portion of axillary region of maxillary barbel, longest at origin of maxillary barbel and two shorter ones posteriorly displaced about half-length of longest one. Main mental barbels short, posterior pair laterally displaced, separated from counterpart by about twice distance of separation between anterior pair. Additional series of barbel-like filaments widespread in ventral portion of head and cleithrum, these longer on adult specimens ( Figs. 1-2). Smaller specimen showing papillary structures in ventral portion of head that seem undeveloped filamentary barbels ( Fig. 2b). Opercular opening small, transversely displaced relative to main body axis and not extended anteriorly, concealed by rounded membranous flap. Opercular openings separated by distance approximating length of one aperture.

Skin roughened with small rounded unculiferous tubercles. Largest tubercles on dorsal portion of head and body, smaller tubercles on ventral surface of body. Small, oblique, slit-like pore at pectoral-fin axilla. No apparent sexual dimorphism. Largest specimen (holotype, 18.5 mm SL) female, with several large eggs visible in ventral and lateral portions of belly ( Fig. 1).

Neurocranium. External surfaces of skull roof bones with pitted texture and somewhat interdigitating sutures between bones. Dorsal surface of neurocranium with pronounced bony knobs at posterior dorsal surface of mesethmoid, anterior portion of frontals at orbit margin, frontal-sphenotic joint, and posterior tip of parietalsupraoccipital. Mesethmoid long and deep; its middle portion constricted in dorsal view. Anterior margin of mesethmoid straight to slightly convex in dorsal view; no medial notch and weakly projected cornua laterally ( Figs. 3-4). Mesethmoid-frontal joint flat, without dorsally projecting processes. Lateral ethmoid elevating dorsoposteriorly to contact frontal, not contributing to dorsal surface of neurocranium. Lateral process of lateral ethmoid extended laterally, articulating with mesial face of autopalatine at its midlength. Frontal moderately compact (length about twice its width), deeply constricted at its middle. Lateral margin of frontal forming concave orbital margin. Frontal-parietal-supraoccipital joint somewhat interdigitating; frontal-sphenotic joint elevating from main cranial surface. Anterior cranial fontanel ovoid, short and wide (its length about half frontal length), its anterior margin surrounded by mesethmoid, remainder by frontals. Posterior cranial fontanel similarly short and wide (slightly broader than anterior cranial fontanel), diamond shaped, enclosed equally by frontal and parietalsupraoccipital ( Fig. 3a). Epiphyseal bar with broad median suture (suture length slightly shorter than length of either cranial fontanel).

Parietal-supraoccipital compact, its greatest length about same as greatest width, somewhat round dorsal view with deep anterior notch Anterior arms of parietal-supraoccipital short, contacting frontal medially and sphenotic laterally. Posterior process of parietal-supraoccipital short, broad and gently rounded, direct contacting anterodorsal edge of dorsal lamina of Weberian apparatus.

Sphenotic somewhat diamond shaped in dorsal view, its posterior margin contacting pterotic laterally; and extensively articulating with hyomandibula anterolaterally. Pterotic somewhat expanded anterolaterally, contacting sphenotic and hyomandibula; anterolateral margin with strongly concave margin. Pterotic wing greatly expanded laterally, tip acute. Supratemporal fossa closed; concavity at its typical position between pterotic and parietal-supraoccipital. Extrascapula absent. Postemporosupracleithrum plate-like with pitted surface, contributing to dorsal aspect of skull; contacting pterotic and parietalsupraoccipital anteriorly and parapophysis of complex vertebrae posteriorly; bordering dorsal fenestra medially; encompassed also by of the Weberian apparatus (posteriorly) and parietal-supraoccipital (anteriorly). Postemporosupracleithrum strongly sutured to surrounding bones, with laterally pointed process overlying dorsal process of cleithrum.

In ventral view of neurocranium ( Fig. 4) vomer absent and parasphenoid relatively short, its anterior margin not surpassing lateral ethmoid; its posterior margin not surpassing prootic; broadest at about its middle portion ( Fig. 4). Orbitosphenoid and pterosphenoid lateroventrally displaced; former four times larger than latter. Prootic somewhat hexagonal in shape, anteriorly contacting sphenotic; having two unossified regions displaced laterally; anterior foramen smaller than posterior one (likely optic and trigemino-facial nerve foramina, respectively). Basioccipital hexagonal in shape, contacting prootic and posterior tip of parasphenoid anteriorly, and Weberian compound vertebra posteriorly. Epiotic apparently absent or fused to exoccipital. Exoccipital not contributing to dorsal surface of neurocranium, and extensively contacting basioccipital.

Suspensorium and oral jaws. Premaxilla ( Fig. 4a) broad and plate-like with anterior and posterior margins somewhat curved, its ventral surface rugose and not presenting bony knobs; teeth absent. Anterior margin of premaxilla with dorsally expanded process aside mesethmoid cornua; posterior margin with rounded process displaced laterally. Premaxilla displaced lateroventrally to ventral margin of mesethmoid, not contacting counterpart medially and articulating laterally with infraorbital 1 ( Fig. 3a). Maxilla ( Figs. 3-4) long and slender, distally bifurcate for about two-thirds its length with its ventral arm longer than dorsal. Anterior portion of maxilla with two rounded articular processes, contacting anterior face of autopalatine. Dentary slender, not contacting counterpart medially; teeth absent ( Fig. 5). Anguloarticular with dorsally expanded process. Anguloarticular strongly fused with retroarticular (boundaries tentatively reconstructed in Fig. 5); both forming socket for joint with quadrate. Coronomeckelian bone absent.

Hyomandibula with well-developed anterodorsal process contacting ventral surface of contact between frontal and sphenotic. Hyomandibula extensively contacting quadrate ventrally by interdigitating suture; fused to preopercle laterally ( Fig. 5). Hyomandibula with elongate posteroventrally directed process and condyle on posterior margin articulating with opercle. Preopercle strongly fused to lateral margin of hyomandibula. Preopercle with welldeveloped, laterally directed expansion, bearing canal, this exiting dorsally and passing through posterolateral portion of expanded hyomandibula before entering pterotic. Suprapreopercle absent. Quadrate subtriangular. Subpreopercle ossified as tubular canal ventral to quadrate. Entopterygoid absent or perhaps fused with anterior portion of metapterygoid. Metapterygoid elongate, constricted at midlength. Anterior margin of metapterygoid reaching lateral process of lateral ethmoid, posterior margin not contacting quadrate or hyomandibula posteriorly. Autopalatine elongate, posterior end rounded, laterally compressed and not bifurcate ( Fig. 3b). Autopalatine articulating with lateral ethmoid at about its posterior third length.

Opercle ( Fig. 5), boomerang shaped with posterior arm about two times longer than ventral arm. Interopercle present, wedge shaped with dorsoposterior margin firmly attached to anterior margin of ventral arm of opercle.

Hyoid and branchial arches. Dorsal hypohyal absent. Ventral hypohyal somewhat triangular in dorsal view, contacting anterior ceratohyal laterally by interdigitating suture ( Fig. 6). Anterior ceratohyal broad, its anterior margin not expanded into blade; greatly expanded posterolateral portion, broader than interdigitating suture with posterior ceratohyal ( Fig. 6). Posterior ceratohyal somewhat triangular in shape, tapering laterally. Interhyal absent. Four branchiostegal rays; outermost (fourth) with anterior half expanded ventrally as posteriorly elongate blade; third branchiostegal expanded posteriorly from its middle to distal portion; remaining branchiostegals 3 and 4 short and slender. Parurohyal, basibranchials and hypobranchials absent. Five ceratobranchials, all bearing short gill rakers ( Fig. 7); fifth ceratobranchial with one or two irregular rows of acicular teeth on dorsal surface along mesial margin. Four epibranchials, first and second slender and third and fourth broader; third epibranchial not bearing typical uncinate process ( Fig. 7). Pharyngobranchials 1-2 and 4 absent. Pharyngobranchial 3 slender; positioned anterolateral to expanded circular tooth plate ( Fig. 7b). Dorsal tooth plate bearing elongate acicular teeth.

Sensory canals and associated structures. Nasal present, small and tubular positioned lateral to constricted portion of mesethmoid ( Fig. 3a). Infraorbital 1 with anteriorly elongated arm curved medially, dorsal to premaxilla and second medially directed acute process on its dorsal surface. Infraorbital canal entering at medial margin of infraorbital 1 just posterior to medially directed process and exiting from posterior posterolateral surface of bone. Remaining infraorbitals reduced to three small, disjointed ossified tubules; infraorbital canal entering anterolateral portion of sphenotic. Sphenotic receiving both infraorbital and supraorbital canals anteriorly. Preopercle-mandibular canal incomplete represented by single short tubular ossification (subpreopercle) anterior to canal entering preopercle; mandibular portion of preopercle-mandibular canal absent. Posterior portion of preopercle-mandibular canal associated with dorsal portion of hyomandibula and entering pterotic posteriorly. Postotic canal exiting from posterior portion of pterotic and entering anterior portion of postemporo-supracleithrum. Pterotic branch and first branch of main lateral line exiting from posteroventral portion of pterotic. Posterior lateral line associated with parapophyses of complex vertebrae of Weberian apparatus, exiting posterolateral portion of that bone and entering posterior lateral-line canal tubules. Posterior lateral line complete reaching hypural region posteriorly. Posterior lateral line canal follow zig-zag course associated with intercalate dorsally and ventrally expanded plate-like structures (lateral plates). Lateral line pores in body, posterior to dorsal-fin origin, associated with elevated posteriorly oriented hookshaped structures of lateral plates ( Fig. 3).

Axial skeleton. Dorsal crest of complex vertebrae of Weberian apparatus reaching dorsal surface of body, its dorsal margin strongly concave anteriorly and rising to elevated hump at its posterior tip ( Fig. 3). Parapophysis of complex vertebrae short, its posterior end narrowed at contact with parapophyses of vertebra 5. Ventral portion of complex vertebrae of Weberian apparatus with ventral process forming ring-like arch over aortic canal and additional laterally directed arm; this arm with expanded thin bony blade surrounding gas bladder anteriorly ( Fig. 4b). Parapophysis of vertebra 5 long, extending beyond lateral limits of parapophysis of vertebra 4 and reaching body wall. Parapophysis of vertebra 5 directed slightly posteriorly with distal margin not distinctly expanded. Anterior nuchal plate absent. Middle nuchal plate smaller than posterior one, somewhat triangular in shape (dorsal view) and contacting posterior nuchal plate posterolaterally and extensively. Middle nuchal plate distant from dorsal crest of complex vertebrae, ventrally contacting vertebrae 6 and 7. Posterior nuchal plate expanded anterolaterally forming elongate wing with rounded lateral end. Posterior nuchal plate lateral wing posteriorly contacting and overlapping dorsolateral process of vertebra 9 ( Fig. 9). Vertebra 9 to last (or penultimate vertebra ventrally) bearing dorso- and ventro-lateral projecting processes, these not overlapping successive ones. Ventrally directed processes of vertebra 9 expanded laterally and bifurcated distally, processes from vertebrae 10 and 11 simple; from 12 and 13 displaced laterally to anal-fin pterygiophore and bifurcated ( Fig. 9). Dorsally and ventrally directed vertebral processes bifid next to dorsal and anal fins; fused medially after last vertebrae associated with pterygiophores of those fins. Two entrances for hemal canal; on anteroventral portions of vertebrae 6 and 9. Hemal and neural spines short not elongate except for hemal spines associated with last two vertebrae; hemal spines associated with anal-fin pterygiophores slightly bifid distally. Consecutive vertebrae with interdigitating articulations between their neural and hemal arches. Ribs absent. Hypurals fused; ventral lobe longer than dorsal one, diastema greatly pronounced. Hypurapophysis elongate and greatly expanded laterally to contact lateral plates.

Fins and girdles. Dorsal-fin I,4. Dorsal-fin spinelet absent. First ray simple (not pungent or rigid), slender but thicker than following branched dorsal-fin rays. Last dorsalfin ray adnate to dorsum by membrane. Adipose fin absent.

Anal fin iv,4; last ray not adnate. Caudal fin with 9 principal rays, 5 in dorsal lobe and 4 in ventral lobe; distal margin obliquely truncate, with lower lobe slightly longer than upper lobe. Outermost principal caudal-fin rays unbranched and expanded proximally. Procurrent caudalfin rays small; difficult to visualize in X-ray.

Pectoral fin I,6. First ray spine-like, not pungent; other fin rays branched. Pectoral-fin spine curved with strong deflection inwards at about its midlength ( Fig. 8a); conspicuously longer than pectoral-fin branched rays. Anterior margin of pectoral-fin spine smooth; posterior margin with 6 or 7 hooks of similar size except two proximal most ones smaller.Three ossified proximal radials associated with pectoral-fin rays; first radial somewhat triangular in shape; positioned within pectoral-spine proximal cleft; remaining two radials elongate and rod shaped. Dorsal portion of cleithrum with two processes: dorsal process long and narrow with lateral cleft; posterior process articulating to ventral portions of postemporo-supracleithrum and parapophysis of complex vertebrae of Weberian apparatus; posterior process somewhat elongate and triangular, pointed distally ( Fig. 8). Cleithrum and scapulocoracoid partly fused, sutures almost indistinguishable. In ventral view, anterior margin of cleithrum transversely straight at and near midline, then deeply concave before prominent joint with pectoral-fin spine (cleithral bulge). Symphysis between cleithrae contacting anteriorly followed by large, circular fenestra on midline, followed posteriorly by heavilyinterdigitating symphyseal suture of scapulocoracoids ( Fig. 4a). Cleithrum bearing two small foramina of similar size on its ventral blade: anteromedial one positioned parallel to anterior concavity of cleithrum ( Fig. 8: f1) and lateral one positioned near articulation with pectoral-fin spine ( Fig. 8: f2). Scapulocoracoid bearing small foramina posterolaterally displaced; positioned lateral to scapulocoracoid posterior process ( Fig. 8: f3). Scapulocoracoid bearing short and posteriorly directed process with somewhat squared distal margin.

Pelvic fin i,5; second ray longest, just reaching analfin origin. Lateral and medial anterior processes of basipterygium weakly developed ( Fig. 10). Basipterygium with smooth anterior and posterior margins, posteriorly with elongate process. Basipterygium with dorsal process positioned at central portion.

Color in alcohol. Head and body yellowish pale, with scattered brownish chromatophores dispersed mostly on dorsal portions. Dark chromatophores concentrated on internarial and interorbital regions and also on dorsal portion over dorsolateral vertebral processes. All fins hyaline. Pale coloration perhaps due to postmortem bleaching during storage in poor quality alcohol and long exposure to light.

Distribution and habitat. Known from three tributaries, which drain southwestern portions of Lake Maracaibo Basin in Zulia State, Venezuela ( Fig. 12). The Caño raya at type locality is a medium size stream (~ 12m wide) with mostly slow flowing white waters running over sand intercalated with riffles of fast flowing waters over pebbles; little marginal and floating vegetation.

Etymology. Hoplomyzon cardosoi is named in honor and memory of a dear colleague who prematurely passed away, Alexandre Rodrigues Cardoso, for his humbleness, positive attitude, and dedicated friendship, and furthermore for his contributions to the taxonomy of Neotropical fishes, including the family Aspredinidae .

Conservation status. Hoplomyzon cardosoi is only known from three localities in the southeastern tributaries of the Lake Maracaibo, with an Area of Occupancy (AOO) of 12 square kilometers, estimated considering a 2 km grid. The Maracaibo Lake has become heavily polluted in the past decades and many mangrove areas have been destroyed or modified by coastal development and land conversion ( Reis et al., 2016). The three collecting events occurred from 1977 to 1982, and intense agriculture developed in the area since then, resulting in continuing decline in habitat quality. Based on the above evidence H. cardosoi can be categorized as Near Threatened (NT) by the IUCN criteria (IUCN, 2016).