Osteology of Tucanoichthys tucano Géry and Römer, an enigmatic miniature fish from the Amazon basin, Brazil (Teleostei: Characiformes: Characidae)

Miniaturization, the evolution of extremely small adult body size, is a common phenomenon across the lineages of freshwater fishes, especially in the Neotropics where over 200 species are considered miniature (≤26 mm in standard length [SL]). Close to 30% of all miniature Neotropical freshwater fishes belong to the family Characidae, several of which are of uncertain phylogenetic placement within the family. We investigate the skeletal anatomy of Tucanoichthys tucano, a species of uncertain phylogenetic position from the upper Rio Negro basin, reaching a maximum known size of 16.6 mm SL. The skeleton of Tucanoichthys is characterized by the complete absence of ten skeletal elements and marked reduction in size and/or complexity of others, especially those elements associated with the cephalic latero-sensory canal system. Missing elements in the skeleton of Tucanoichthys include those that develop relatively late in the ossification sequence of the non-miniature characiform Salminus brasiliensis, suggesting that their absence in Tucanoichthys can be explained by a simple scenario of developmental truncation. A number of the reductions in the skeleton of Tucanoichthys are shared with other miniature characiforms, most notably species of Priocharax and Tyttobrycon, the latter a putative close relative of Tucanoichthys based on molecular data.

A Review of Sculpins (COTTOIDEI) of Middle Asia with a Revalidation of the Species Cottus jaxartensis and Description of a New Species Cottus nudus sp. nova

Abstract— Based on the investigations of the representatives of the genus Cottus from Middle Asia, the species status of C. spinulosus is supported, and its diagnostic characters are specified. The validity of С.jaxartensis is resumed and a degree of its distinction from C. gobio is evaluated. A comparative analysis of morphological characters of the C. nasalis holotype and С.jaxartensis specimens of the same body size shows identity of these species, and, thus, C.nasalis has been included in the synonymy of C.jaxartensis. A new species C. nudus sp. nova is described. The representatives of this species differ from other Asian species of the genus in the following characters: absence of bony spickles nd dermal tubercles on the skin of the head and trunk; elongated upper jaw terminated near the vertical through posterior margin of orbit; presence of teeth on palatine bones; short sensory canal on the trunk with 23 pores; monochrome light coloration of the fins; and widened distal ends of neural and/or hemal spines in seven caudal centra. A key for the identification of three Middle Asian species (C. spinulosus, C. jaxartensis, and C.nudus sp. nova) is given.

Gross morphology of the cephalic sensory canal pores in Patagonian toothfish Dissostichus eleginoides Smitt, 1898 from southern Chile (Perciformes: Nototheniidae)

This study describes the cephalic sensory canal pores of the Patagonian toothfish's juvenile and adult specimens (Dissostichus eleginoides) from southern Chile. Specimens exhibited four supraorbital, eight infraorbital, and five mandibular pores, followed by six preoperculars, one coronal pore, one supratemporal pore, and four temporal pores. Juveniles exhibited circular pores in the mandibular, infraorbital, and preopercular region. The first two supraorbital pores are circular, the third is rectangular, and the fourth triangular. The coronal pore is circular with a bifurcation; the supratemporal pore is rectangular. In adults, the first mandibular canal pore is circular, and the last four are elongated. The preopercular canal pores are elongated. The two first supraorbital canal pores are circular, unlike the third and fourth, which are rectangular. The coronal pore is rectangular without bifurcation, and the supratemporal pore has a T-shape. The jaw of juveniles does not present all mandibular canal pores; in the infraorbital region, the first five pores extend as a thin canaliculus, while the adjacent pores appear as longer canaliculi in adults. The differences could be related to changes in spatial distribution during larval, juvenile, and adult stages. Adult cephalic sensory canal pores may have an important role in detecting vibratory waves allowing them to capture their prey and perceive potential predators. Our results provide information regarding the cephalic sensory canal pores of the Patagonian toothfish that may stimulate future studies of this species' mechanosensory system.

Tanyrhinichthys mcallisteri, a long-rostrumed Pennsylvanian ray-finned fish (Actinopterygii) and the simultaneous appearance of novel ecomorphologies in Late Palaeozoic fishes

The Carboniferous radiation of fishes was marked by the convergent appearance of then-novel but now common ecomorphologies resulting from changes in the relative proportions of traits, including elongation of the front of the skull (rostrum). The earliest ray-finned fishes (Actinopterygii) with elongate rostra are poorly known, obscuring the earliest appearances of a now widespread feature in actinopterygians. We redescribe Tanyrhinichthys mcallisteri, a long-rostrumed actinopterygian from the Upper Pennsylvanian (Missourian) of the Kinney Brick Quarry, New Mexico. Tanyrhinichthys has a lengthened rostrum bearing a sensory canal, ventrally inserted paired fins, posteriorly placed median fins unequal in size and shape, and a heterocercal caudal fin. Tanyrhinichthys shares these features with sturgeons, but lacks chondrostean synapomorphies, indicating convergence on a bottom-feeding lifestyle. Elongate rostra evolved independently in two lineages of bottom-dwelling, freshwater actinopterygians in the Late Pennsylvanian of Euramerica, as well as in at least one North American chondrichthyan (Bandringa rayi). The near-simultaneous appearance of novel ecomorphologies among multiple, distantly related lineages of actinopterygians and chondrichthyans was common during the Carboniferous radiation of fishes. This may reflect global shifts in marine and freshwater ecosystems and environments during the Carboniferous favouring such ecomorphologies, or it may have been contingent on the plasticity of early actinopterygians and chondrichthyans.

A new genus of sinogaleaspids (Galeaspida, stem-Gnathostomata) from the Silurian Period in Jiangxi, China

Galeaspids are an endemic clade of jawless stem-gnathostomes known as ostracoderms. Their existence illuminates how specific characteristics developed in jawed vertebrates. Sinogaleaspids are of particular interest among the galeaspids but their monophyly is controversial because little is known about Sinogaleaspis xikengensis. Newly discovered sinogaleaspids from the Lower Silurian of Jiangxi, China provide a wealth of data and diagnostic features used to establish the new genus, Rumporostralis gen. nov., for Sinogaleaspis xikengensis. A morphological study showed that the sensory canal system of sinogaleaspids had mosaic features similar to those of three known galeaspids. There are 3–8 pairs of transverse canals in the Sinogaleaspidae, which suggests that the sensory canal system of galeaspid probably had a grid distribution with transverse canals arranged throughout the cephalic division. Phylogenetic analysis of Galeaspida supports the monophyly of the Sinogaleaspidae, consisting of Sinogaleaspis, Rumporostralis, and Anjiaspis. However, Shuyu and Meishanaspis form another monophyletic group, Shuyuidae fam. nov., which is outside all other eugaleaspidiforms. We propose a cladistically-based classification of Galeaspida based on our analysis.

Sphyraena stellata, a new barracuda from the Indo-Pacific, with redescriptions of S. helleri Jenkins, 1901 and S. novaehollandiae Günther, 1860 (Perciformes: Sphyraenidae)

A new barracuda, Sphyraena stellata, is described on the basis of 41 specimens [98.0–587.0 mm standard length (SL)] collected from the Indo-Pacific. The new species can be distinguished from all congeners in having the following combination of characters: one gill raker on first gill arch; pelvic-fin insertion located slightly before vertical through first dorsal-fin origin; pored lateral-line scales 134–141 (modally 137), total lateral-line scales 139–148 (146); scales above and below lateral line 15–17 (15) and 14–16 (15), respectively; snout comparatively short, its length 13.6–15.8 (mean 14.4) % SL; upper jaw short, its posterior tip not reaching to below anterior nostril, its length 10.0–12.2 (10.8) % SL; eye small, orbit diameter and depth 4.3–7.0 (4.9) and 3.9–5.6 (4.5) % SL, respectively; anal-fin base shortish, its length 6.9–8.1 (7.5) % SL; last dorsal- and anal-fin ray lengths 4.0–5.6 (4.7) and 3.6–5.6 (4.6) % SL, respectively; anus not close to anal-fin origin, anterior and posterior margins of former to anal-fin origin 7.5–11.9 (9.9) and 5.2–8.3 (6.8) % of head length, respectively; head sensory canal pores on suborbital area simple or slightly branched, their lowermost parts not close to margin of lacrimal bone, large smooth area lacking canal pores on mid-margin of lacrimal bone; two yellow stripes on lateral surface of body (remaining as black stripes in preserved specimens); and caudal fin gray. In addition, S. helleri Jenkins, 1901 and S. novaehollandiae Günther, 1860, both being closely related to the new species, are redescribed on the basis of 4 (243.3–545.8 mm SL) and 15 (270.8–598.0 mm SL) specimens, including holotypes, respectively, with new diagnostic characters proposed for both species.

A new species of Terelabrus (Perciformes: Labridae) from the Philippines with a key to species of Terelabrus and new record of Terelabrus dewapyle

A new labrid fish, Terelabrus zonalis sp. nov., the fourth species of the genus, is described on the basis of two specimens collected from the Philippines. The new species is characterized by 44 longitudinal series scale rows, 42 pored lateral-line scales, 11–12 gill rakers (including rudiments), the main supratemporal sensory canal with 8 branches posteriorly, the area bounded by the main supratemporal and postotic sensory canals (dorsal view) with 3 scale rows, the least distance between the orbit anteroventral margin and interopercle 7.0% of standard length and 18 faint silver vertical bands on the body in preserved specimens. An underwater photograph of T. dewapyle is reported as the first record of the species from the Philippines. A key to species of Terelabrus is provided.

New species of Trichomycterus (Siluriformes: Trichomycteridae) from the High Andean Plateau of Argentina

Trichomycterus varii new species, is described from a small tributary of the High Andean Plateau Region, Jujuy, Argentina. The new species is distinguished from other species of Trichomycterus by the following characters: the caudal peduncle expanded in the area of procurrent caudal-fin rays, distal tip of pelvic fin not reaching the anus when depressed, the presence of fronto-lachrymal tendon bone without lateral process, the first pectoral-fin ray terminating at the margin of the fin, the distal margin of pectoral-fin rounded, seven pectoral fin rays, 15–19 interopercular odontodes, the supraorbital sensory canal with the presence of pore s3, the infraorbital sensory canal segment with the presence of pores i1 and i3, the laterosensory canal of trunk with three sensory pores, 16 pairs of ribs, 11 precaudal vertebrae, and 25 caudal vertebrae. It closely resembles T. yuska and T. pseudosilvinichthys from northwestern Argentina and western Bolivia, but differs in head canal sensory pattern.

On the occurrence of Vinctifer ferrusquiai sp. nov. (Actinopterygii, Aspidorhynchiformes) in the Kimmeridgian (Late Jurassic) deposits near Tlaxiaco, Oaxaca, southern Mexico

Vinctifer ferrusquiai sp. nov. is described in this paper. This aspidorhynchid fish was found in Kimmeridgian marine deposits of the Sabinal Formation, exposed in the Llano Yosobé, near Tlaxiaco, Oaxaca, Mexico. The single specimen of this species shows enough diagnostic characters to be included in the order Aspidorhynchiformes, the family Aspidorhynchidae, and the genus Vinctifer. These characters include an elongate rostrum consisting of the premaxillae fused and anteriorly elongated, forming a tube-like, as well as an preopercular sensory canal located close to the posterior edge of the preopercle. Other features are the lack of premaxilla, the development of a wide posterior expansion of the maxilla, and a stout triangular preopercle. A unique combination of characters supports the erection of this new species, whose ganoine on dermal bones of the head are strongly ornamented with tubercles and ridges, and the flank scales are entirely smooth and not serrated. This Jurassic record is the first indubitable pre-Cretaceous finding of Vinctifer, the oldest into the Hispanic Corridor, and the oldest in North America.

New information on Brindabellaspis stensioi Young, 1980, highlights morphological disparity in Early Devonian placoderms

Acid-prepared specimens of the placoderm Brindabellaspis stensioi (Early Devonian of New South Wales, Australia) revealed placoderm endocranial anatomy in unprecedented detail. Brindabellaspis has become a key taxon in discussions of early gnathostome phylogeny, and the question of placoderm monophyly versus paraphyly. The anterior orientation of the facial nerve and related hyoid arch structures in this taxon resemble fossil osteostracans (jawless vertebrates) rather than other early gnathostomes. New specimens of Brindabellaspis now reveal the previously unknown anterior region of the skull, including an exceptionally elongate premedian bone forming a long rostrum, supported by a thin extension of the postethmo-occipital unit of the braincase. Lateral overlap surfaces indicate an unusual anterior position for the jaws. Digital rendering of a synchrotron radiation scan reveals a uniquely specialized ethmoid commissure sensory canal, doubled back and fused into a midline canal. The visceral surface of the premedian bone has a plexus of perichondral bone canals. An updated skull roof reconstruction of Brindabellaspis adds to the highly variable dermal skull patterns of the probably non-monophyletic ‘acanthothoracids'. The unusual morphology revealed by the new specimens suggests that the earliest known reef fish fauna contained a diverse range of fishes with specialized ecological roles.