A new gelatinous host for pelagic fishes: First in situ record of an association between driftfishes (Stromateiformes, Ariommatidae) and nudibranchs (Mollusca, Phylliroidae).

We describe the first recorded association between fishes and nudibranchs in epipelagic waters. In situ observations and photographs of a juvenile spotted driftfish Ariomma regulus (Stromateiformes; Ariommatidae) swimming alongside the planktonic nudibranch Phylliroe lichtensteinii (Gastropoda; Phylliroidae) were made during blackwater scuba dives off Palm Beach, Florida, United States of America. In this paper, we describe this behavior, highlighting a previously undocumented zooplanktonic host used by fishes. This finding also demonstrates the importance of community science in advancing our understanding of the early life history of marine species.

The importance of the appendicular skeleton for the phylogenetic reconstruction of lamniform sharks (Chondrichthyes: Elasmobranchii).

Lamniform sharks are one of the more conspicuous groups of elasmobranchs, including several emblematic taxa as the white shark. Although their monophyly is well supported, the interrelationships of taxa within Lamniformes remains controversial because of the conflict among various previous molecular-based and morphology-based phylogenetic hypotheses. In this study, we use 31 characters related to the appendicular skeleton of lamniforms and demonstrate their ability to resolve the systematic interrelationships within this shark order. In particular, the new additional skeletal characters resolve all polytomies that were present in previous morphology-based phylogenetic analyses of lamniforms. Our study demonstrates the strength of incorporating new morphological data for phylogenetic reconstructions.

NEOTROPICAL FRESHWATER FISHES: A dataset of occurrence and abundance of freshwater fishes in the Neotropics.

The Neotropical region hosts 4225 freshwater fish species, ranking first among the world's most diverse regions for freshwater fishes. Our NEOTROPICAL FRESHWATER FISHES data set is the first to produce a large-scale Neotropical freshwater fish inventory, covering the entire Neotropical region from Mexico and the Caribbean in the north to the southern limits in Argentina, Paraguay, Chile, and Uruguay. We compiled 185,787 distribution records, with unique georeferenced coordinates, for the 4225 species, represented by occurrence and abundance data. The number of species for the most numerous orders are as follows: Characiformes (1289), Siluriformes (1384), Cichliformes (354), Cyprinodontiformes (245), and Gymnotiformes (135). The most recorded species was the characid Astyanax fasciatus (4696 records). We registered 116,802 distribution records for native species, compared to 1802 distribution records for nonnative species. The main aim of the NEOTROPICAL FRESHWATER FISHES data set was to make these occurrence and abundance data accessible for international researchers to develop ecological and macroecological studies, from local to regional scales, with focal fish species, families, or orders. We anticipate that the NEOTROPICAL FRESHWATER FISHES data set will be valuable for studies on a wide range of ecological processes, such as trophic cascades, fishery pressure, the effects of habitat loss and fragmentation, and the impacts of species invasion and climate change. There are no copyright restrictions on the data, and please cite this data paper when using the data in publications.

The critical role of natural history museums in advancing eDNA for biodiversity studies: a case study with Amazonian fishes.

Ichthyological surveys have traditionally been conducted using whole-specimen, capture-based sampling with varied but conventional fishing gear. Recently, environmental DNA (eDNA) metabarcoding has emerged as a complementary, and possible alternative, approach to whole-specimen methodologies. In the tropics, where much of the diversity remains undescribed, vast reaches continue unexplored, and anthropogenic activities are constant threats; there have been few eDNA attempts for ichthyological inventories. We tested the discriminatory power of eDNA using MiFish primers with existing public reference libraries and compared this with capture-based methods in two distinct ecosystems in the megadiverse Amazon basin. In our study, eDNA provided an accurate snapshot of the fishes at higher taxonomic levels and corroborated its effectiveness to detect specialized fish assemblages. Some flaws in fish metabarcoding studies are routine issues addressed in natural history museums. Thus, by expanding their archives and adopting a series of initiatives linking collection-based research, training and outreach, natural history museums can enable the effective use of eDNA to survey Earth's hotspots of biodiversity before taxa go extinct. Our project surveying poorly explored rivers and using DNA vouchered archives to build metabarcoding libraries for Neotropical fishes can serve as a model of this protocol.

A new species of sexually dimorphic and rheophilic ghost knifefish (Apteronotidae: Gymnotiformes) from the Amazon basin.

A new species of ghost knifefish, Apteronotus, is described from high-energy environments in the Rios Mapuera and Trombetas (at Cachoeira Porteira waterfalls), Brazil. X-ray microcomputed tomography (µCT scan) was used to access the internal anatomy of the type series. The new species is distinguished from all congeners by the anteriormost position of the anus, with its posterior margin extending less than one eye diameter beyond the vertical through the caudal limit of the posterior nostril, the low number of anal-fin rays (117-125) and the reduced number of branchiostegal rays (three). A series of modifications associated with secondary sexual dimorphism on the preorbital region of mature males are depicted and discussed. In addition, comments on homologies of the branchiostegal rays in Apteronotidae are provided.

A reappraisal of the pectoral skeleton of lantern sharks (Elasmobranchii: Squaliformes: Etmopteridae).

The morphology of the articular region of the pectoral girdle and associated basals in Etmopteridae is revised in light of new evidence provided by taxa unavailable for previous studies. Such studies considered that etmopterids plesiomorphically had a single pectoral articular condyle, and only Etmopterus had two separate ones. Our reanalysis indicates that the possession of two separate condyles, one for the articulation of the propterygium and the second for the meso- and metapterygium, is the most widespread condition in this group. However, the presence of two separate articular condyles is not recovered as a synapomorphy for Etmopteridae. Previous studies also proposed that etmopterids lack a hook-like process on the anteroproximal margin of the anteriormost pectoral basal. We document that the hook-like process is plesiomorphically present in Etmopteridae, thus corroborating the hypothesis of closer relationships between this family and the other squaliforms that also share this process, namely Centrophoridae, Dalatiidae, Oxynotidae, and Somniosidae.

Anatomy and evolution of the pectoral filaments of threadfins (Polynemidae).

The most remarkable anatomical specialization of threadfins (Percomorphacea: Polynemidae) is the division of their pectoral fin into an upper, unmodified fin and a lower portion with rays highly modified into specialized filaments. Such filaments are usually elongate, free from interradial membrane, and move independently from the unmodified fin to explore the environment. The evolution of the pectoral filaments involved several morphological modifications herein detailed for the first time. The posterior articular facet of the coracoid greatly expands anteroventrally during development. Similar expansions occur in pectoral radials 3 and 4, with the former usually acquiring indentations with the surrounding bones and losing association with both rays and filaments. Whereas most percomorphs typically have four or five muscles serving the pectoral fin, adult polynemids have up to 11 independent divisions in the intrinsic pectoral musculature. The main adductor and abductor muscles masses of the pectoral system are completely divided into two muscle segments, each independently serving the pectoral-fin rays (dorsally) and the pectoral filaments (ventrally). Based on the innervation pattern and the discovery of terminal buds in the external surface of the filaments, we demonstrate for the first time that the pectoral filaments of threadfins have both tactile and gustatory functions.

Anatomy and ontogenetic changes of the facial and gular musculature of the tetra Astyanax brucutu: A remarkable case of adaptation to durophagy.

Astyanax brucutu is a peculiar species of Neotropical tetra endemic from the Chapada Diamantina, a large plateau in northeastern Brazil. Individuals of this species undergo a dramatic ontogenetic shift in their diet that is accompanied by equally remarkable changes in their feeding apparatus. Whereas juveniles of A. brucutu feed mostly on algae, adults feed almost exclusively on an endemic species of hydrobiid snail and other associated living organisms that inhabit their dead shells (including infaunal invertebrates and algae). Skeletal adaptations associated with this change in diet were previously reported, but until now, the changes in the musculature remained mostly unknown. The present paper describes the facial and gular muscles, as well as the buccal ligaments of A. brucutu in different life stages, and identifies the major ontogenetic changes in these systems associated with the diet shift in the species. Such changes primarily involve expansions of specific portions of the adductor mandibulae and associated tendons and ligaments that likely represent adaptations to increase the biting power necessary to crush copious amounts of shells ingested by larger individuals of A. brucutu. Those adaptations are absent in specimens of any size of Astyanax cf. fasciatus, a sympatric congener lacking durophagous feeding habits. Anatomical comparisons and landmark-based principal components analysis (PCA) suggest that most specializations to durophagy in A. brucutu arose by peramorphosis. We also found that several of the muscular specializations of adults of A. brucutu are paralleled in species of Creagrutus and Piabina, two other characid genera distantly related to Astyanax, but that also feed on hard food items.

Facial and gill musculature of polynemid fishes, with notes on their possible relationships with sciaenids (Percomorphacea: Perciformes).

The Polynemidae is a family of primarily marine fishes with eight genera and 42 extant species. Many aspects of their morphology are largely unknown, with few reports about their osteology and barely any information on their myology. This paper describes and illustrates in detail all facial and branchial muscles of representative species of polynemids. Our analysis demonstrates the existence of several remarkable and previously unknown specializations in the polynemid musculature. The aponeurotic and completely independent origin of the pars promalaris of the adductor mandibulae is apparently unique among percomorphs. The differentiation of this section into lateral and medial subsections; the total separation of the promalaris from the retromalaris; the differentiation of the pars primordialis of the levator arcus palatini into external and internal subsections are also uncommon features of polynemids that are shared by sciaenids, thus supporting the hypothesis of a closer relationship between these families.

Phylogenomic analysis of trichomycterid catfishes (Teleostei: Siluriformes) inferred from ultraconserved elements.

The family Trichomycteridae is one of the most diverse groups of freshwater catfishes in South and Central America with eight subfamilies, 41 genera and more than 300 valid species. Its members are widely distributed throughout South America, reaching Costa Rica in Central America and are recognized by extraordinary anatomical specializations and trophic diversity. In order to assess the phylogenetic relationships of Trichomycteridae, we collected sequence data from ultraconserved elements (UCEs) of the genome from 141 specimens of Trichomycteridae and 12 outgroup species. We used a concatenated matrix to assess the phylogenetic relationships by Bayesian inference (BI) and maximum likelihood (ML) searches and a coalescent analysis of species trees. The results show a highly resolved phylogeny with broad agreement among the three distinct analyses, providing overwhelming support for the monophyletic status of subfamily Trichomycterinae including Ituglanis and Scleronema. Previous relationship hypotheses among subfamilies are strongly corroborated, such as the sister relationship between Copionodontinae and Trichogeninae forming a sister clade to the remaining trichomycterids and the intrafamilial clade TSVSG (Tridentinae-Stegophilinae-Vandelliinae-Sarcoglanidinae-Glanapteryginae). Monophyly of Glanapteryginae and Sarcoglanidinae was not supported and the enigmatic Potamoglanis is placed outside Tridentinae.

Anatomical, taxonomic, and phylogenetic reappraisal of a poorly known ghost knifefish, Tembeassu marauna (Ostariophysi: Gymnotiformes), using X-ray microcomputed tomography.

A detailed osteological study of the poorly known and critical endangered ghost knifefish, Tembeassu marauna, from the rio Paraná, Brazil, was conducted using X-ray microcomputed tomography (µCT scan). A redescription of the external anatomy was performed, including the unusual presence of a rostral patch of extra teeth on the region of the upper lip anterior to the premaxilla and the prominent anterior fleshy expansions in both upper and lower lips. The newly surveyed characters were included and analyzed in light of a recent morphological data matrix for Gymnotiformes. In spite of some uncertainties that remains as to phylogenetic allocation of the genus, the most probable hypothesis is that Tembeassu is the sister group of a clade that includes Megadontognathus and Apteronotus sensu stricto. The phylogenetic analysis also supports that Tembeassu is considered a valid genus of Apteronotidae. An amended diagnosis for the genus is also provided.

Phylogenetic interrelationships of the eel families Derichthyidae and Colocongridae (Elopomorpha: Anguilliformes) based on the pectoral skeleton.

A cladistic analysis of the eel families Derichthyidae and Colocongridae is herein proposed for the first time on the basis of morphological data. We discovered dozens of new phylogenetic characters derived from a detailed analysis of the pectoral skeleton, an anatomical system neglected by most previous studies. Our maximum parsimony analysis indicates that Colocongridae sensu lato is paraphyletic, with its two constituent genera Coloconger and Congriscus appearing as successive sister groups of derichthyids. Monophyly of the family Derichthyidae, which has been questioned by some studies, is herein strongly supported by 10 unambiguous synapomorphies. We also stress the importance of the appendicular skeleton as a useful source of phylogenetic information for the resolution of systematic problems within Anguilliformes.

Evolution of the facial musculature in basal ray-finned fishes.

BACKGROUND: The facial musculature is a remarkable anatomical complex involved in vital activities of fishes, such as food capture and gill ventilation. The evolution of the facial muscles is largely unknown in most major fish lineages, such as the Actinopterygii. This megadiverse group includes all ray-finned fishes and comprises approximately half of the living vertebrate species. The Polypteriformes, Acipenseriformes, Lepisosteiformes, Amiiformes, Elopiformes, and Hiodontiformes occupy basal positions in the actinopterygian phylogeny and a comparative study of their facial musculature is crucial for understanding the cranial evolution of bony fishes (Osteichthyes) as a whole. RESULTS: The facial musculature of basal actinopterygians is revised, redescribed, and analyzed under an evolutionary perspective. We identified twenty main muscle components ontogenetically and evolutionarily derived from three primordial muscles. Homologies of these components are clarified and serve as basis for the proposition of a standardized and unifying myological terminology for all ray-finned fishes. The evolutionary changes in the facial musculature are optimized on the osteichthyan tree and several new synapomorphies are identified for its largest clades, including the Actinopterygii, Neopterygii, and Teleostei. Myological data alone ambiguously support the monophyly of the Holostei. A newly identified specialization constitutes the first unequivocal morphological synapomorphy for the Elopiformes. The myological survey additionally allowed a reinterpretation of the homologies of ossifications in the upper jaw of acipenseriforms. CONCLUSIONS: The facial musculature proved to be extremely informative for the higher-level phylogeny of bony fishes. These muscles have undergone remarkable changes during the early radiation of ray-finned fishes, with significant implications for the knowledge of the musculoskeletal evolution of both derived actinopterygians and lobe-finned fishes (Sarcopterygii).

Multilocus analysis of the catfish family Trichomycteridae (Teleostei: Ostariophysi: Siluriformes) supporting a monophyletic Trichomycterinae.

Trichomycteridae is the second most diverse family of the order Siluriformes, its members are widely distributed through the freshwaters of Central and South America, exhibiting an exceptional ecological and phenotypic disparity. The most diverse subfamily, Trichomycterinae, represented mainly by the genus Trichomycterus, historically has been recognized as non-monophyletic and various characters used to unite or divide its constituents are repeatedly called into question. No comprehensive molecular phylogenetic hypothesis regarding relationships of trichomycterids has been produced, and the present study is the first extensive phylogeny for the family Trichomycteridae, based on a multilocus dataset of three mitochondrial loci and two nuclear markers (3284bp total). Our analysis has the most comprehensive taxon-sampling of the Trichomycteridae published so far, including members of all subfamilies and a vast representation of Trichomycterus diversity. Analysis of these data showed a phylogenetic hypothesis with broad agreement between the Bayesian (BI) and maximum-likelihood (ML) trees. The results provided overwhelming support for the monophyletic status of Copionodontinae, Stegophilinae, Trichomycterinae, and Vandelliinae, but not Sarcoglanidinae and Glanapteryginae. A major feature of our results is the support to the current conceptualization of Trichomycterinae, which includes Ituglanis and Scleronema and excludes the "Trichomycterus" hasemani group. Divergence time analysis based on DNA substitution rates suggested a Lower Cretaceous origin of the family and the divergence events at subfamilial level shaped by Paleogene events in the geohistory of South America. This hypothesis lays a foundation for an array of future studies of evolution and biogeography of the family.

A new species of Ituglanis (Siluriformes: Trichomycteridae) from the Tocantins and Paranaíba river basins, central Brazil, with remarks on the systematics of the genus.

Ituglanis goya, new species, is described from the Paranaíba and Tocantins river drainages, central Brazil. This is the first species of the genus described for the Upper Paraná system and the second epigean Ituglanis for the Tocantins basin. The new species is distinguished from its congeners by the combination of a color pattern formed by longitudinal stripes and spots, absence of the anterior cranial fontanel, pattern of the cephalic laterosensory system and several fin-ray counts. Ituglanis goya exhibits morphological features that oppose the traditional hypotheses of alignment of the genus with the TSVSG clade of Trichomycteridae. These and other issues concerning the systematics of Ituglanis and the Trichomycterinae are critically discussed.

The infrabranchial musculature and its bearing on the phylogeny of percomorph fishes (Osteichthyes: Teleostei).

The muscles serving the ventral portion of the gill arches ( = infrabranchial musculature) are poorly known in bony fishes. A comparative analysis of the infrabranchial muscles in the major percomorph lineages reveals a large amount of phylogenetically-relevant information. Characters derived from this anatomical system are identified and discussed in light of current hypotheses of phylogenetic relationships among percomorphs. New evidence supports a sister-group relationship between the Batrachoidiformes and Lophiiformes and between the Callionymoidei and Gobiesocoidei. Investigated data also corroborate the existence of two monophyletic groups, one including the Pristolepididae, Badidae, and Nandidae, and a second clade consisting of all non-amarsipid stromateiforms. New synapomorphies are proposed for the Atherinomorphae, Blenniiformes, Lophiiformes, Scombroidei (including Sphyraenidae), and Gobiiformes. Within the latter order, the Rhyacichthyidae and Odontobutidae are supported as the successive sister families of all remaining gobiiforms. The present analysis further confirms the validity of infrabranchial musculature characters previously proposed to support the grouping of the Mugiliformes with the Atherinomorphae and the monophyly of the Labriformes with the possible inclusion of the Pholidichthyiformes. Interestingly, most hypotheses of relationships supported by the infrabranchial musculature have been advanced by preceding anatomists on the basis of distinct data sources, but were never recovered in recent molecular phylogenies. These conflicts clearly indicate the current unsatisfactory resolution of the higher-level phylogeny of percomorphs.

A new species of Ituglanis from the Rio Xingu Basin, Brazil, and the evolution of pelvic fin loss in trichomycterid catfishes (Teleostei: Siluriformes: Trichomycteridae).

A new species of the trichomycterid catfish genus Ituglanis is described from the Rio Curuá, Rio Xingu basin, Rio Amazonas drainage, Brazil. Ituglanis apteryx, new species, is promptly distinguished from congeners, except some specimens of I. parahybae (Eigenmann), by the absence of pelvic fins, girdle, and muscles. The new species differs from I. parahybae in the pattern of the cephalic laterosensory system; the absence of a posterior cranial fontanel; the presence of an epural; and the number of branchiostegal rays, ribs, and vertebrae. Ituglanis apteryx is one among the several trichomycterids lacking pelvic fins. Analysis reveals that pelvic fin loss independently evolved several times during the trichomycterid radiation.

The jaw adductor muscle complex in teleostean fishes: evolution, homologies and revised nomenclature (osteichthyes: actinopterygii).

The infraclass Teleostei is a highly diversified group of bony fishes that encompasses 96% of all species of living fishes and almost half of extant vertebrates. Evolution of various morphological complexes in teleosts, particularly those involving soft anatomy, remains poorly understood. Notable among these problematic complexes is the adductor mandibulae, the muscle that provides the primary force for jaw adduction and mouth closure and whose architecture varies from a simple arrangement of two segments to an intricate complex of up to ten discrete subdivisions. The present study analyzed multiple morphological attributes of the adductor mandibulae in representatives of 53 of the 55 extant teleostean orders, as well as significant information from the literature in order to elucidate the homologies of the main subdivisions of this muscle. The traditional alphanumeric terminology applied to the four main divisions of the adductor mandibulae - A1, A2, A3, and Aω - patently fails to reflect homologous components of that muscle across the expanse of the Teleostei. Some features traditionally used as landmarks for identification of some divisions of the adductor mandibulae proved highly variable across the Teleostei; notably the insertion on the maxilla and the position of muscle components relative to the path of the ramus mandibularis trigeminus nerve. The evolutionary model of gain and loss of sections of the adductor mandibulae most commonly adopted under the alphanumeric system additionally proved ontogenetically incongruent and less parsimonious than a model of subdivision and coalescence of facial muscle sections. Results of the analysis demonstrate the impossibility of adapting the alphanumeric terminology so as to reflect homologous entities across the spectrum of teleosts. A new nomenclatural scheme is proposed in order to achieve congruence between homology and nomenclature of the adductor mandibulae components across the entire Teleostei.

Monophyly of the Agoniatinae (Characiformes: Characidae).

The Characidae is the most diverse family of Neotropical fishes, currently encompassing more than one thousand valid species. Some subgroups within this family still lack phylogenetic definitions, being diagnosed on the basis of combination of characters, a common procedure in pre-cladistic studies. Agoniatinae, currently composed by two valid species, Agoniates anchovia and A. halecinus, is one of them. In the present study the Agoniatinae is redefined using a phylogenetically oriented comparative survey that included the two Agoniates species plus 114 species representing all the major clades of the Characidae and their closest relatives. Six derived morphological characters are identified as synapomorphies for the Agoniatinae: deep notch on the posterior region of the maxilla joining the ventral margin of the infraorbital 2; dentigerous portion of premaxilla shorter than the ascending process of this bone; dentary canine preceded by tricuspid teeth; ventral margin of the urohyal markedly convex; base of the uppermost ray of the ventral lobe of the caudal fin much expanded, being as deep as the distal margin of hypural 2; and levator arcus palatini muscle with a posterodorsal bundle of fibers attaching to the dorsal face of the sphenotic spine.