Scott A. Schaefer

Postotic laterosensory canal and pterotic branch homology in catfishes

Morphology of the postotic laterosensory canal was surveyed across loricarioid and outgroup catfishes in order to resolve conflicting statements regarding homology and phylogenetic significance of intrinsic character variation. A pterotic branch is widespread among catfishes and has been identified as a synapomorphy for siluriforms, but its presence in loricarioid catfishes has been disputed. In contrast to previous statements that absence of a pterotic branch is synapomorphic for loricarioids, we confirm the presence of a pterotic branch in Nematogenys inermis and other trichomycterids, callichthyids, and loricariids. The pterotic branch is secondarily absent in scoloplacids and astroblepids. We present criteria for establishing homology of the pterotic branch and review character state optimization schemes on the currently accepted phylogeny. The postotic region of loricariids is further specialized in having an expanded swimbladder capsule that incorporates the trunk lateral line canal and has a lateral opening covered by a greatly expanded pterotic complex. The trunk lateral line enters the swimbladder capsule mesial to the pterotic lateral wall and passes anteromedially as a fleshy tube before forming the postotic canal in the pterotic, a morphology reported previously for a single loricariid representative. Variation in the relative extent and topographic position of postotic canal branches and other morphologies is diagnostic of certain loricariid taxa, suggesting a rich character complex of potential utility in phylogeny reconstruction. J. Morphol. 246:212–227, 2000.

The Temporal Region of the Cranium of Loricarioid Catfishes (Teleostei: Siluriformes): Morphological Diversity and Phylogenetic Significance

Abstract The morphology of the temporal region of the cranium of the monophyletic loricarioid catfishes was examined in representatives of the families Trichomycteridae, Callichthyidae, Scoloplacidae, Astroblepidae, and Loricariidae, and compared to non-loricarioid outgroup taxa. The results indicate the presence of derived specializations in the morphology of the pterotic bone, swimbladder capsule, lateral-line nerve, and associated structures which have not been previously recognized. Astroblepids, callichthyids, loricariids and scoloplacids differ from trichomycterids and non-loricarioid catfishes in having a reduced number of bones in the temporal region. Loricariids share with astroblepids and some trichomycterids the presence of direct contact between the trunk lateral-line canal and swimbladder capsule chamber; however, only loricariids have the lateral-line canal in direct contact with the swimbladder membrane, resulting in a laterophysic connection in addition to the otophysic connection between inner ear and swimbladder characteristic of otophysan fishes. Derived trichomycterids share with the outgroups Amphiliidae, Plotosidae and Sisoridae a cranial exit of the posterior lateral-line nerve separate from that of the vagus nerve, whereas both nerves exit the cranium via a common foramen in other loricarioids and outgroup catfishes. Callichthyids share with scoloplacids and loricariids a lateral-line nerve traversing the swimbladder capsule. Loricariids are further modified in having a compound pterotic bone that is double-layered and bears the postotic canal on the ventral layer. The dorsal layer is posteriorly expanded to enclose the lateral opening of the swimbladder capsule and an expanded capsule chamber. Based on the previously well-established scheme of interrelationships among loricarioid families, we infer that much of the variation in temporal cranial morphology over the course of loricarioid evolution has involved independent convergence toward increased functional association of primitively separate sensory structures of the octavolateralis system.

The Lithogeninae (Siluriformes, Loricariidae): Anatomy, Interrelationships, and Description of a New Species

Abstract A new species of the loricariid genus Lithogenes Eigenmann, 1909, is described on the basis of 84 specimens captured from a single locality in the upper Río Orinoco drainage of southern Venezuela. The new species is only the third representative of the subfamily Lithogeninae to be recognized in the 100 years since the discovery of the type species, L. villosus, and is the only lithogenine known from more than a handful of specimens. This new material provides the basis for a comprehensive review of lithogenine systematics, comparative anatomy, and interrelationships. Lithogenes wahari, new species, shares with its congeners the dermal plates of the trunk comprised of three paired series, presence of a bifurcate levator arcus palatini crest and expanded lateral lamina of the hyomandibula, and the palatine sesamoid not reaching the nasal capsule, thus confirming its placement in Lithogenes among the Loricariidae. The new species is diagnosed among congeners by the absence of odontodes on the proximal portion of the ventral surface of the first pelvic-fin ray (vs. ventral pad covered with embedded odontodes along entire length) and thickened skin of the pelvic pad forming extensive ridges; accessory premaxillary teeth absent; anal fin with intense pigment band along base and diffuse spot at midlength of fin rays (vs. pigment band at base absent, fin rays dusky, without distinct spot). Characters useful for distinguishing lithogenine species are reviewed; revised diagnoses and descriptions are provided for the two previously described species in light of new character evidence. A detailed comparative analysis of the osteology and myology of L. wahari is presented and discussed relative to homologous conditions observed more broadly among the loricarioid catfishes. Of particular importance are aspects of musculoskeletal anatomy that are hitherto unknown for lithogenines, and aspects of sexual dimorphism and the anatomy of the reproductive and digestive systems that are unique or unusual among loricariid catfishes. A phylogenetic analysis of relationships among species based on morphological characters places the two Guyana Shield species (L. villosus and L.wahari) as sister taxa on the basis of four synapomorphies. Both species share reduction in the width and extent of the jaws, resulting in the derived reduction in the numbers of teeth carried by the jaw elements. Evaluated with respect to the geographic distribution of the species, the pattern of phylogenetic relationships suggests an ancestral widespread distribution for the Lithogeninae throughout the Guyana Shield plus the Caribbean and eastern Andean foreland basin of northern South America, followed by vicariance and subsequent divergence of populations now isolated in the coastal mountains of northern Venezuela and the Guyana Shield region. Lithogenine catfishes share a number of unique features with astroblepid catfishes that are not observed to occur in other members of the Loricariidae, such as the morphology of the pelvic fins, specialized pelvic musculature, and associated adaptations for climbing. Evaluated against the evidence supporting their phylogenetic placement as the sister group to all other Loricariidae, exclusive of the Astroblepidae, these shared similarities suggest that the association with rocky habitats of headwater stream systems and the ability to climb vertical surfaces may represent ancestral conditions for the lineage leading to the astroblepid plus loricariid catfishes.

New and Noteworthy Venezuelan Glanapterygine Catfishes (Siluriformes, Trichomycteridae), with Discussion of Their Biogeography and Psammophily

Abstract Four new species of the trichomycterid subfamily Glanapteryginae are described from the Río Orinoco basin of Venezuela. Two new species each in Pygidianops Myers 1944 and Typhlobelus Myers 1944 represent the first documented occurrence of these genera in Venezuela, and for Pygidianops the first occurrence outside the Río Negro basin. The new species were captured from sand-bottom habitats in two disparate locations in the Orinoco River basin and display a remarkable suite of reductive features, such as loss of eyes, fins, and pigment, and reductions or absence of laterosensory canals and odontodes. Pygidianops cuao, n.sp. from the Río Cuao, a clear-water tributary of the upper Orinoco River, is diagnosed from its congeners by the presence of diminutive eyes and a triangular skin flap at the corner of the mouth. Pygidianops magoi, n.sp., known from near the delta of the Orinoco River, is diagnosed from its congeners by the absence of pectoral and anal fins, presence of four laterosensory pores, and nine or ten caudal-fin rays. Typhlobelus guacamaya, n.sp. from the Río Cuao is diagnosed relative to its congeners by the presence of three branchiostegal rays, posterior naris absent, lack of pleural ribs, and is further distinguished from both T. ternetzi and T. macromycterus by the absence of eyes and from T. lundbergi by the presence of three laterosensory canal pores. Typhlobelus lundbergi, n.sp. from the lower Orinoco is diagnosed by the presence of four laterosensory canal pores and further distinguished from T. ternetzi and T. macromycterus by the absence of eyes. We review the characters useful in diagnoses of Pygidianops and Typhlobelus among trichomycterid catfishes and discuss morphological patterns in the diversification of the Glanapteryginae. Species of Pygidianops and Typhlobelus are known only from the rivers draining the Guyana and Brazilian shields, yet within these areas they occupy all major water types. Such broad ecological range suggests that the geographic distribution of species of these two genera are not limited by water type. That observation, plus their common occurrence in the ubiquitous shallow sand-bottom habitats of the larger rivers of the shield regions of northern South America, indicate that species of Pygidianops and Typhlobelus may be expected to occur throughout the entire Amazon and Orinoco basins. The evolution of habitat preference in glanapterygines seems to follow a trend toward increased specialization for interstitial environments. The degree of psammophilic adaptation in species of Pygidianops and Typhlobelus is remarkable, without parallel in siluriforms and perhaps in any other freshwater fishes. We describe the physical characteristics of the sand and review the suite of morphological specializations for life in interstitial sand that are shared by these species, such as loss or reduction of certain structures and presence in these species of paired metapleural keels along the ventral edges of the abdomen formed by a long ridge of stiffened integument, underlain by well-differentiated medial infracarinalis muscles, that are superficially similar to the metapleural folds of sand-dwelling cephalochordates and other interstitial organisms.

New Trichomycterus (Siluriformes: Trichomycteridae) from an Offshore Island of Colombia

Abstract Trichomycterus gorgona, the first insular trichomycterid species, is described from a small stream on Gorgona Island, located approximately 56 km west of the Pacific coast of Colombia. The new species differs from all congeners in the possession of a thick transverse skin flap between the pelvic fins. It is further distinguished by the following combination of characteristics: presence of eight or nine paired ribs (vs 12 or more), reduced pigmentation, and eyes reduced to small ovoid dots. Although epigean, the new species shares features commonly observed among troglomorphs, yet is distinguished from troglobitic Trichomycterinae in having the maxillary barbel extending to the anterior pectoral-fin margin, nasal barbels reaching the opercular odontodes, three supraorbital pores on the head (vs four pores), eight pectoral-fin rays (vs nine or 10) and the first ray prolonged as a filament, tip of adpressed pelvic-fin not reaching anal-fin origin (vs reaching origin of anal-fin), 39 or 40 vertebrae (vs 35 or 36), eight to 13 opercular odontodes (vs 15 or 16), 14 or 15 interopercular odontodes (vs 30 to 37). In consideration of its peculiar insular distribution, we offer extensive comparisons of the new species to congeners distributed in proximate coastal drainages. Trichomycterus gorgona, primera especie insular de tricomictérido, es descripta de un arroyo pequeño de la Isla Gorgona, localizada aproximadamente a 56 km al oeste de la costa del Océano Pacífico de Colombia. La nueva especie difiere de todos los congéneres por poseer un grueso repliegue de tegumento entre las aletas pélvicas. Se diferencia además por la siguiente combinación de características: presencia de ocho o nueve pares de costillas (vs 12 o más), pigmentación reducida y ojos reducidos a pequeños puntos negros. Si bien epigea, la nueva especie comparte caracteres observados comunmente entre los troglomorfos, pero se diferencia de los Trichomycterinae troglobitas en tener las barbillas maxilares extendidas hasta el margen anterior de la aleta pectoral, las barbillas nasales alcanzan los odontoides operculares, tres poros supraorbitales en la cabeza (vs cuatro poros), ocho radios en la aleta pectoral (vs nueve o diez) y el primer radio prolongado como un filamento, extremo de la aleta pélvica no alcanza el origen de la alaeta anal (vs alcanza el origen de la aleta anal), 39 o 40 vértebras (vs 35 o 36), ocho a 13 odontoides operculares (vs 15 o 16), 14 o 15 odontoides interoperculares (vs 30 a 37). Teniendo en cuenta su distribución insular peculiar, ofrecemos una amplia comparación de la nueva especie con los congéneres distribuídos en cuencas próximas a la costa.

A New Species of Hisonotus (Siluriformes, Loricariidae) of the Upper Río Uruguay Basin

Abstract A new species of the hypoptopomatine genus Hisonotus (Loricariidae) is described from a small tributary of the upper río Uruguay basin near the border between Uruguay and Brazil. The new species can be distinguished from all other congeners by the following combination of characters: (1) presence of serrae along distal two thirds of posterior margin of pectoral-fin spine (versus serrae absent, posterior margin smooth); (2) odontodes along anterior margin of snout biserially arranged, dorsad and ventrad series separated by narrow odontode-free area covered by pad of soft tissue; (3) caudal peduncle short (27–34% SL, versus > 34% SL) and deep (13–15 % SL, versus < 13% SL); (4) eye large (15–19% HL, versus < 13% HL); and (5) caudal-fin pigmentation, when well defined, dark brown with a pair of whitish blotches on upper and lower lobes. The significance of the distribution of the new species is discussed relative to the degree of endemism of other fish groups in the Uruguay basin.

Redescription of the Pez Graso, Rhizosomichthys totae (Trichomycteridae), of Lago de Tota, Colombia, and Aspects of Cranial Osteology Revealed by Microtomography

Abstract Rhizosomichthys totae, the Pez Grasso, greasefish, or runcho of Lago de Tota, Colombia, is known from ten specimens and thought to be extinct. The species is unique among trichomycterids in possessing remarkable rings of extensive adipose tissues surrounding the body. Although its internal anatomy is poorly known, diagnosis of Rhizosomichthys totae and taxonomic status within Trichomycteridae have not been questioned. Non-destructive reconstruction of the osteology of one paratype based on computed microtomography, combined with broad character surveys of representatives of other trichomycterid genera, formed the basis for a redescription of R. totae and revealed the presence of four additional autapomorphies involving features of the cranium, autopalatine, and branchiostegal rays. This evidence further confirms the membership of Rhizosomichthys within the putatively non-monophyletic subfamily Trichomycterinae. We evaluate in R. totae the characters serving to diagnose the genera presently included in the Trichomycterinae. Rhizosomichthys totae, el Pez Grasso, bagre gordo, o runcho del Lago de Tota, Colombia, es conocido de diez ejemplares y se piensa extinto. La especie es única entre los tricomictéridos en poseer marcados anillos de abundante tejido adiposo rodeando el cuerpo. Aunque su anatomía interna es conocida pobremente, la diagnosis de Rhizosomichthys totae y el estatus taxonómico no ha sido cuestionado dentro de Trichomycteridae. Reconstrucción osteológica no destructiva de un paratipo basado en microtomografía computada, combinada con un amplia búsqueda de caracteres en representantes de otros géneros de tricomictéridos, constituye la base para la redescripción de R. totae y revela la presencia de cuatro autopomorfías adicionales involucrando rasgos del cráneo, autopalatino, y radios branquiostegos. Esta evidencia además lo confirma como miembro de Rhizosomichthys dentro de la no monofilética subfamilia Trichomycterinae. En R. totae evaluamos los caracteres que sirven para diagnosis del género, actualmente incluido en los Trichomycterinae.

Relationships among the Neotropical Candirus (Trichomycteridae, Siluriformes) and the evolution of parasitism based on analysis of mitochondrial and nuclear gene sequences

Phylogenetic relationships among the trichomycterid catfishes are investigated for the first time using molecular sequence data. Data derived from mitochondrial and nuclear DNA sequences for representatives of 17 genera were analyzed to test previous hypotheses of relationships among trichomycterid subfamilies, the monophyly of the subfamily Stegophilinae, and the monophyly and relationships among the genera of parasitic members of the family. We analyzed 2325 aligned base-pairs from mitochondrial 12S, 16S, ND4 (tRNA(His) tRNA(Ser)), and the nuclear histone H3 gene for representatives of 10 of 12 stegophiline and 3 of 4 vandelliine genera, plus 10 outgroup taxa selected to represent the range of subfamilial diversity. Maximum parsimony and likelihood approaches resolved a monophyletic semiparasitic Stegophilinae as the sister-group of the obligate hematophagous Vandelliinae. At the level of subfamilies, the pattern of relationships of the parasitic members among the remainder of the family is fully congruent with the most recent hypothesis of relationships for trichomycterids based exclusively on morphological data. Within stegophilines, our results differ from multiple previous morphological studies in recovery of (1) Haemomaster and Ochmacanthus as sister-taxa, (2) the morphologically plesiomorphic Pareidon microps nested within a relatively distal part of the tree topology, (3) Apomatoceros as sister to Henonemus, rather than to the morphologically similar Megalocentor. These result indicate that parasitism arose once and was unreversed within the Trichomycteridae. Survey of diet and feeding morphology among trichomycterids suggests that the semiparasitic lifestyle of the members of the Stegophilinae was retained in the enigmatic Pareiodon microps, despite reversal to the generalized trichomycterid condition of the associated morphological specializations found in all other stegophilines. These results further support the reconstruction of semiparasitism, rather than blood feeding, for the shared common ancestor of the parasitic Trichomycteridae.

New, Possibly Extinct Lithogenine Loricariid (Siluriformes, Loricariidae) from Northern Venezuela

Abstract A new species of the previously monotypic loricariid subfamily Lithogeninae is described from northern Venezuela. Lithogenes valencia is the first representative of the subfamily to be discovered subsequent to the discovery and description of Lithogenes villosus Eigenmann, 1909, from Guyana and extends the geographic distribution of the subfamily beyond the Guyana Shield region of northeastern South America. The new species shares several derived features with L. villosus that are not observed among other Loricariidae. It is diagnosed from L. villosus by the broader head, 27–29% SL (vs 22% SL), 25–29 premaxillary teeth (vs 9–10), the presence of nine (vs 8) branched pectoral-fin rays, anal fin rays ii,5 (vs ii,7), straight (vs sickle-shaped) lateropterygium, and by the presence of small plates in the dorsal and ventral series of the lateral trunk irregularly arranged and not contacting the plates of the median series (vs plates larger, regularly arranged in series, in contact with the median series plates posteriorly). Lithogenes valencia is known only from six specimens collected from the basin of Lago de Valencia, an endorrheic lake basin occupying a tectonic graben situated between the coastal and interior ranges of the Cordillera de La Costa of north-central Venezuela. Subsequent collecting efforts have failed to obtain additional specimens and the species may now be extinct, since the lake and its tributaries have become severely degraded by pollution and disturbance. Aspects of its peculiar morphology are described and illustrated, and we provide evidence for its sister-group relationship to L. villosus. Presently isolated and undergoing rapid desiccation and contamination, Lago de Valencia had a recent connection with the Orinoco River to the south. Although dispersal into the lake basin via this relatively recent connection is possible, it is argued instead that consideration of its habitat and phylogenetic position as a basal representative of the Loricariidae indicate that a more ancient biogeographic explanation may be responsible for its unexpected occurrence in the northern Caribbean coastal region.

Systematics of the Genus Hypoptopoma Günther, 1868 (Siluriformes, Loricariidae)

Abstract The systematics of Hypoptopoma Günther (1868a) is revised based on comprehensive evaluation of specimen collections and a phylogenetic analysis of the species. The genus Hypoptopoma comprises a distinctive assemblage of loricariid catfishes distributed in the lowland drainages of tropical, subtropical, and temperate latitudes of South America to the east of the Andes. Hypoptopoma is uniquely diagnosed among genera of the Loricariidae on the basis of the presence of a laterally expanded nuchal plate. Members of the genus can be further distinguished from all other loricariids, except the hypoptopomatin genus Oxyropsis, by the depressed head with eyes placed ventrolateral and visible from below. Hypoptopoma is further distinguished from all other Hypoptopomatini, including Oxyropsis, by the caudal peduncle posterior to the base of the anal fin ovoid in cross section and deeper in the dorsoventral axis. All species of Hypoptopoma, except H. spectabile, can be further distinguished among loricariids by the presence in adult stages of a column of variably enlarged and flattened odontodes positioned along the posterior margin of the trunk plates. Individuals of several Hypoptopoma species attain the largest body size for the subfamily Hypoptopomatinae, with standard length reaching 105 mm. Species of Hypoptopoma typically occur in streams of slow to moderate current and muddy to sandy bottom with marginal emergent vegetation. Based on verified specimen records, the species is distributed in the Río Amazonas basin, including the Ucayali, Madeira, and Tapajos rivers, as well as in the rivers east to the Ilha Marajo drainage (Para, Brazil), in the Tocantins and smaller coastal river drainages in northeastern Brazil (Mearim), the upper Río Orinoco basin, the Essequibo and Nickerie river basins of the Guiana Shield, and in the ríos Paraguay and lower Paraná. There are no records of Hypoptopoma in the Río Uruguay, the Atlantic coastal drainages of Uruguay and Brazil south of Rio Mearim (Maranão), the upper Paraná, and Rio São Francisco systems. Fifteen species are recognized in Hypoptopoma, seven of which are newly described herein. Phylogenetic analysis of Hypoptopoma species, based on analysis of 26 characters drawn from aspects of external morphology and internal osteology, recovered a well-supported but incompletely resolved nested set of clade relationships that suggests a widespread ancestral distribution for the group in central Amazonia, plus at least four instances of divergence of a species having a peripheral distribution from an Amazonian sister group. Relationships at the basal node were unresolved. There was insufficient evidence to resolve the relationships among H. baileyi, n. sp., of the Madeira river basin, an unresolved clade comprised of H. guianense Boesemann, 1974, of the Essequibo and Nickerie basins in Guyana and Surinam; H. psilogaster Fowler, 1915, of the upper Amazon basin in Brazil and Peru; and H. thoracatum Günther, 1868a, of the upper and middle Amazon basin; and a well-supported clade that includes all other Hypoptopoma species. The latter clade was supported by four synapomorphies and includes H. brevirostratum, n. sp., of the upper Amazon basin in Brazil and Peru, H. muzuspi, n. sp., of the Tocantins basin, and a more restricted clade supported by six character-state changes comprising the remainder of the subfamily. Two species, H. spectabile (Eigenmann, 1914) of the upland Amazon and upper Orinoco river basins of Venezuela, Colombia, Ecuador, and Peru and H. sternoptychum (Schaefer, 1996a) of the lowland reaches of the Amazon river, formerly placed in the genus Nannoptopoma Schaefer, 1996, represent a clade most closely related to a nested subset of Hypoptopoma species. These former Nannoptopoma species are reassigned to Hypoptopoma, thus rendering the former generic name a subjective junior synonym of Hypoptopoma. Hypoptopoma bianale, n. sp., of the upper Amazon River basin in Brazil and Peru represents the sister group to a largely unresolved clade comprised of H. inexspectatum (Holmberg, 1893a) of the Paraguay-Paraná basin, H. steindachneri Boulenger, 1895, of the upper Amazon basin in Brazil and Peru, H. gulare Cope, 1878, of the upper Amazon basin, H. machadoi, n. sp., of the Orinoco basin, and a clade comprised of H. elongatum, n. sp., of the lower Tapajos and lower Trombetas rivers plus H. incognitum, n. sp., of the middle Amazon basin, Tocantins, and Mearim rivers. A key to the species of Hypoptopoma is provided.