The adductor mandibulae muscle complex in lower teleostean fishes (Osteichthyes: Actinopterygii): comparative anatomy, synonymy, and phylogenetic implications

Coelacanths illuminate deep-time evolution of cranial musculature in jawed vertebrates

Coelacanths are rare fishes that occupy a key evolutionary position in the vertebrate tree of life. Despite being exhaustively studied, we found that a substantial part of the knowledge on their cranial musculature was mistaken. Eleven previously reported coelacanth "muscles" are nonexistent, while three previously unknown muscle subdivisions and connections are found. These findings markedly affect our understanding of the deep-time cranial evolution of jawed vertebrates (gnathostomes). Only 13% of the previously identified myological evolutionary novelties for the major gnathostome lineages proved to be accurate, but several new ones are proposed. We show that low, moderate, and high levels of cranial muscle innovation characterized the emergence of lobe-finned (sarcopterygian), cartilaginous (chondrichthyan), and ray-finned (actinopterygian) fishes, respectively. The novelties in the latter group resulted in the evolution of a second active mechanism for the expansion of the oropharyngeal cavity, which was probably crucial for the predominance of suction feeding versus bite feeding in extant actinopterygians.

Kinetic comparisons of jaw opening, jaw closing and locomotor muscles

Understanding contraction dynamics of skeletal muscle is critically important to appreciate performance capabilities of skeletal structures, especially for structures responsible for feeding and/or locomotion. Furthermore, it is important to understand how temperature can impact contraction dynamics in vertebrates that are regularly exposed to fluctuations in temperature. We aimed to address differences between jaw opening (sternhyoideus), jaw closing (adductor mandibulae) and locomotor (abductor superficialis) muscle contraction dynamics in a labrid fish. Additionally, we aimed to understand how temperature changes impact contraction kinetics in these muscles. To address these aims we collected cunner (Tautogolabrus adspersus) from Long Island Sound and removed their primary locomotor and jaw opening/closing muscles. Following dissection, the muscles were placed on a muscle ergometer that controlled length, stimulus duration and stimulation intensity. Muscles were exposed to 7, 15 and 22 °C for all experiments. We found that the swimming muscle was slower to contract and relax than both feeding muscles. Swimming muscle produced more power than feeding muscles when tested at 8 Hz and 15 °C. Jaw closing muscle produced more force than the other two muscle types when tested at22 °C. Despite these differences, muscle contraction kinetics were remarkably similar across the three muscle types and temperatures. To our knowledge this is the first study to measure in vitro contraction dynamics of fish jaw opening and closing muscle. This advances the understanding of the physiological capabilities of these muscles. Additionally, differences in contraction dynamics can further our understanding of the physiological limits temperature impart on whole muscle contraction.

Facial and opercular muscles in the Anguilliformes (Elopomorpha: Teleostei): Comparative anatomy and phylogenetic implications for the basal position of Protanguilla

The teleost order Anguilliformes, true eels, comprises more than 1000 described species in 20 families, commonly known as eels, congers, morays, and gulper eels. Comprehensive studies of Anguilliformes are limited, resulting in a lack of consensus for morphology-based phylogenetic hypotheses. A detailed morphological analysis of the cephalic and opercular myology offers a promising new source of characters to help elucidate the intrarelationships of Anguilliformes. Our study is the most extensive myological analysis for the group and includes 97 terminal taxa, with representatives from each of the 20 families of Anguilliformes plus outgroup clades. Results demonstrate that muscle characters inform phylogenetic relationships within Anguilliformes, and we propose two new synapomorphies for all extant members, including Protanguilla palau, the "living fossil"-adductor mandibulae originating on the parietal (vs. restricted to suspensorium) and segmentum mandibularis absent (vs. present). Exceptions for the first condition characterize highly modified saccopharyngoids, and for the second one, Notacanthidae. More importantly, we suggest three new synapomorphies for the remaining extant anguilliforms (except in highly modified saccopharyngoids)-adductor mandibulae originates on the frontals (vs. frontals naked), adductor mandibulae stegalis is separated from the rictalis (vs. ricto-stegalis fused into a single piece), and the levator operculi inserts on the lateral surface of the opercle (vs. medial surface of the opercle). Our phylogenetic optimization strongly corroborates the hypothesis that Protanguilla is the sister group of all other extant eels. A further goal of this paper is to clearly document the substantive conflicts between the available molecular data and the extensive and diverse morphological evidence.

Patterns of diversification and phylogenetic structure in the dorsolateral head musculature of Neotropical electric eels (Ostariophysi: Gymnotiformes), with a myological synonymy

Abstract The present study offers a broad comparative analysis of the dorsolateral head musculature in the Gymnotiformes, with detailed descriptions and illustrations of the dorsolateral head muscles of 83 species representing combined all valid genera. Results permit a detailed assessment of primary homologies and taxonomically-relevant variation across the order. This provides the basis for a myological synonymy, which organizes 33 previously proposed names for 15 recognized muscles. Morphological variation derived from dorsolateral head musculature was coded into 56 characters. When analyzed in isolation, that set of characters results in Gymnotidae as the sister group of remaining gymnotiforms, and all other currently recognized families as monophyletic groups. In a second analysis, myological characters were concatenated with other previously proposed characters into a phenotypic matrix. Results of that analysis reveal new myological synapomorphies for nearly all taxonomic categories within Gymnotiformes. A Partitioned Bremer Support (PBS) was used to asses the significance of comparative myology in elucidating phylogenetic relationships. PBS values show strongly non-uniform distributions on the tree, with positive scores skewed towards more inclusive taxa, and negative PBS values concentrated on less inclusive clades. Our results provide background for future studies on biomechanical constraints evolved in the early stages of gymnotiform evolution.

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.

Encephalon gross morphology of the cichlid Geophagus sveni (Cichlidae: Geophagini): Comparative description and ecological perspectives

The encephalon gross morphology of Geophagus sveni is described, compared between male and female specimens and discussed in relation to evolutionary, ecological and behavioural aspects. The Student's t-test revealed that there are no sexual dimorphism regarding the volume or linear measurements obtained from the main encephalon subdivisions (telencephalon, tectum mesencephali, cerebellum, gustative lobes, hypothalamus and hypophysis) in proportion to encephalon length, which is congruent with the absence of external dimorphic characters and presence of biparental care behaviour. In all specimens examined, the tectum mesencephali is the largest structure of the encephalon, which may be explained by feeding habit and by the importance of the vision center in a social context (i.e., brood guarding and territory defence, which are common behaviours in cichlids). Also, the lobus vagi is more developed than usual for other teleosts, which may be explained by the presence, in G. sveni as well as in other Geophagini species, of a differentiated pharyngeal apparatus, probably an adaptation to winnowing, a specialized feeding habit. The little intraspecific variation in neuroanatomical characters observed herein indicates a possible source of morphological characters to be explored in cichlid phylogeny.

The bite force-gape relationship as an avenue of biomechanical adaptation to trophic niche in two salmonid fishes

All skeletal muscles produce their largest forces at a single optimal length, losing force when stretched or shortened. In vertebrate feeding systems, this fundamental force-length relationship translates to variation in bite force across gape, which affects the food types that can be eaten effectively. We measured the bite force-gape curves of two sympatric species: king salmon (Oncorhynchus tshawytscha) and pink salmon (Oncorhynchusgorbuscha). Cranial anatomical measurements were not significantly different between species; however, peak bite forces were produced at significantly different gapes. Maximum bite force was achieved at 67% of maximum gape for king salmon and 43% of maximum gape for pink salmon. This may allow king salmon to use greater force when eating large or elusive prey. In contrast, pink salmon do not require high forces at extreme gapes for filter feeding. Our results illustrate that the bite force-gape relationship is an important ecophysiological axis of variation.

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.

Phylogenetic systematics of the driftwood catfishes (Siluriformes: Auchenipteridae): a combined morphological and molecular analysis

A comprehensive phylogeny of species relationships of the Auchenipteridae is reconstructed here with a large-scale taxon sampling based on combined morphological and molecular datasets. The hypothesized phylogeny includes most species of Auchenipteridae (97 of 124 valid species) and multiple members of siluriform families as an outgroup (32 species) to embrace the diversity of forms among related catfishes. As the first large-scale phylogeny of the Auchenipteridae, comparison between taxa included information from both morphology (264 characters) and mitochondrial and nuclear molecular markers (3490 nucleotides) from five genes: coI, 16S, rag2, myh6 and SH3PX3. Trees were generated under two different optimality criteria (Maximum Parsimony and Bayesian Inference). A new classification for the family is presented herein to bring the taxonomy more in line with the new phylogenetic hypothesis. The strict consensus tree corroborates the monophyly of superfamily Doradoidea, family Auchenipteridae and its two subfamilies, Centromochlinae and Auchenipterinae. The new classification scheme proposes nine tribes in Auchenipteridae, based on the monophyly of major groups in both subfamilies. Centromochlus, Glanidium and Tatia are each recovered as paraphyletic. To maintain a monophyletic classification, some species treated as Tatia and Centromochlus are assigned to genera not previously recognized as valid.

A new species of Eigenmannia Jordan & Evermann (Gymnotiformes: Sternopygidae) from rio Tapajós, Brazil, with discussion on its species group and the myology within Eigenmanniinae

A new species of Eigenmannia is described from the rio Mutum, tributary of upper rio Juruena, rio Tapajós basin, Comodoro, Mato Grosso, Brazil. The new species is distinguished from all congeners by coloration pattern, position of the mouth, number of scales rows above lateral line, number of premaxillary and dentary teeth, number of precaudal vertebrae, orbital diameter, mouth width, relative depth of posterodorsal expansion on infraorbitals 1+2 and relative size of coronomeckelian bone. Comments on potentially useful characters in phylogenetic studies derived from musculature, discussion on Eigenmannia species-group and the first dichotomous key for Eigenmannia are provided.

A digital dissection of two teleost fishes: comparative functional anatomy of the cranial musculoskeletal system in pike (Esox lucius) and eel (Anguilla anguilla)

Advances in X-ray computed tomography (CT) have led to a rise in the use of non-destructive imaging methods in comparative anatomy. Among these is contrast-enhanced CT scanning, which employs chemical stains to visualize soft tissues. Specimens may then be 'digitally dissected', producing detailed, three-dimensional digital reconstructions of the soft- and hard-tissue anatomy, allowing examination of anatomical structures in situ and making accurate measurements (lengths, volumes, etc.). Here, we apply this technique to two species of teleost fish, providing one of the first comprehensive three-dimensional (3D) descriptions of teleost cranial soft tissue and quantifying differences in muscle anatomy that may be related to differences in feeding ecology. Two species with different feeding ecologies were stained, scanned and imaged to create digital 3D musculoskeletal reconstructions: Esox lucius (Northern Pike), predominantly a suction feeder; and Anguilla anguilla (European eel), which captures prey predominantly by biting. Muscle cross-sectional areas were calculated and compared between taxa, focusing on muscles that serve important roles in feeding. The adductor mandibulae complex - used in biting - was larger in Esox than Anguilla relative to head size. However, the overall architecture of the adductor mandibulae was also very different between the two species, with that of Anguilla better optimized for delivering forceful bites. Levator arcus palatini and sternohyoideus - which are used in suction feeding - are larger in Esox, whereas the levator operculi is larger in Anguilla. Therefore, differences in the size of functionally important muscles do not necessarily correlate neatly with presumed differences in feeding mode.

The South American and Australian percichthyids and perciliids. What is new about them?

ABSTRACT A study including morphological characters and mitogenomics of South American and Australian fishes previously assigned to Percichthyidae was conducted. Results generated from these different data sets reveal major disagreements concerning the content and interpretation of the so-called percichthyids. A phylogenetic analysis based on 54 morphological characters suggests the existence of two major clades: (1) Percichthyidae, including the South American Percichthys and the Australian taxa Macquaria australasica, Macquaria (= Plectroplites), and Maccullochella; (2) Perciliidae with the South American genus Percilia at the base plus more advanced Australian genera Nannoperca, Nannatherina, Bostockia, and Gadopsis. In contrast, molecular and mitogenomic evidence suggests only one clade (Percichthyidae), with the exclusion of species of Macquaria (= Percalates). Additionally, the results reveal the existence of various taxonomic problems, such as the current interpretation of only one species of Percichthys in Argentina, an interpretation that is not supported by the present study; the existence of cryptic species of Percilia as well as of Gadopsis, Nannoperca, and Macquaria that will increase the diversity of the genera; and the need for an extensive revision of species previously assigned to Percalates versus Macquaria. Disagreements point to the need to develop further research on the so-called percichthyids and perciliids.

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).

Comparative gross encephalon morphology in Callichthyidae (Teleostei: Ostariophysi: Siluriformes)

ABSTRACT Callichthyidae comprises the subfamilies Callichthyinae and Corydoradinae, both of which are morphologically distinct and monophyletic. Although there is consensus regarding the monophyly of the family, the relationships of about 80% of its species, currently included in the genus Corydoras, remain poorly known. Despite the vast amount of osteological information for Teleostei, knowledge regarding the phylogenetic implications of encephalon anatomy is sparse and represents a poorly explored source of potential characters. The present study aims to describe the encephalon morphology in members of the Callichthyidae in order to propose new characters that may help address phylogenetic questions regarding this group. In addition to representatives of Callichthyidae, specimens belonging to the Nematogenyidae, Trichomycteridae, Scoloplacidae, Astroblepidae and Loricariidae were dissected for comparative purposes. Head dissection revealed information on the structure of the medulla spinalis, rhombencephalon, mesencephalon, diencephalon and telencephalon. The conditions observed on the encephalons examined suggest that representatives of Callichthyidae have great taste perception and processing, while Corydoradinae stand out for visual acuity and Callichthyinae for mechanoreception processing subunits. Our results also indicate that the encephalon has important features for systematic studies of the family bringing greater resolution to current phylogenetic hypotheses.

Evolution of skeletal and muscular morphology within the functionally integrated lower jaw adduction system of sculpins and relatives (Cottoidei)

Vertebrate lever mechanics are defined by the morphology of skeletal elements and the properties of their muscular actuators; these metrics characterize functional diversity. The components of lever systems work in coordination ("functional integration") and may show strong covariation across evolutionary history ("evolutionary integration"), both of which have been hypothesized to constrain phenotypic diversity. We quantified evolutionary integration in a functionally integrated system - the lower jaw of sculpins and relatives (Actinopterygii: Cottoidei). Sculpins primarily rely on suction feeding for prey capture, but there is considerable variation in evasiveness of their prey, resulting in variation in anatomy of the lower jaw-closing mechanism. We used functionally-relevant linear measurements to characterize skeletal and muscular components of this system among 25 cottoid species and two outgroup Hexagrammoidei (greenling) species. We quantified evolutionary covariation and correlation of jaw-closing mechanical advantage (i.e., skeletal leverage) and muscle architecture (i.e., gearing) by correlating phylogenetically independent contrasts and fitting phylogenetically corrected generalized least squares models. We found no evidence of evolutionary covariation in muscle architecture and skeletal leverage. While we found a positive evolutionary correlation between out-lever length and adductor muscle fiber length, there was no significant evolutionary correlation between in-lever length and adductor muscle fiber length. We also found a positive evolutionary correlation between in- and out-lever lengths. These results suggest that skeletal morphology and muscle morphology contribute independently to biomechanical diversity among closely related species, indicating the importance of considering both skeletal and muscular variation in studies of ecomorphological diversification.

From the inside out: a new species of armoured catfish Corydoras with the description of poorly-explored character sources (Teleostei, Siluriformes, Callichthyidae)

A new species of the armoured catfish genus Corydoras is described from the Xingu-Tapajos ecoregion, Brazilian Amazon. The new species can be distinguished from its congeners by having the following combination of features: short mesethmoid, with anterior tip poorly developed, smaller than 50% of bone length; posterior margin of pectoral spine with serrations directed towards spine tip or perpendicularly oriented; infraorbital 2 only in contact with sphenotic; ventral laminar expansion of infraorbital 1 poorly or moderately developed; flank midline covered by small dark brown or black saddles with similar size to remaining markings on body; relatively larger, scarcer and more sparsely distributed dark brown or black spots on body; absence of stripe on flank midline; caudal fin with conspicuous dark brown or black spots along its entire surface; slender body; and strongly narrow frontals. A more comprehensive description of poorly-explored internal character sources, such as the gross morphology of the brain, Weberian apparatus and swimbladder capsule elements is presented.

Development of the muscles associated with the mandibular and hyoid arches in the Siberian sturgeon, Acipenser baerii (Acipenseriformes: Acipenseridae)

The skeleton of the jaws and neurocranium of sturgeons (Acipenseridae) are connected only through the hyoid arch. This arrangement allows considerable protrusion and retraction of the jaws and is highly specialized among ray-finned fishes (Actinopterygii). To better understand the unique morphology and the evolution of the jaw apparatus in Acipenseridae, we investigated the development of the muscles of the mandibular and hyoid arches of the Siberian sturgeon, Acipenser baerii. We used a combination of antibody staining and formalin-induced fluorescence of tissues imaged with confocal microscopy and subsequent three-dimensional reconstruction. These data were analyzed to address the identity of previously controversial and newly discovered muscle portions. Our results indicate that the anlagen of the muscles in A. baerii develop similarly to those of other actinopterygians, although they differ by not differentiating into distinct muscles. This is exemplified by the subpartitioning of the m. adductor mandibulae as well as the massive m. protractor hyomandibulae, for which we found a previously undescribed portion in each. The importance of paedomorphosis for the evolution of Acipenseriformes has been discussed before and our results indicate that the muscles of the mandibular and the hyoid may be another example for heterochronic evolution.

The brain of Brycon orbignyanus (Valenciennes, 1850) (Teleostei: Characiformes: Bryconidae): gross morphology and phylogenetic considerations

ABSTRACT The brain of Brycon orbignyanus is described as a model for future studies of the gross morphology of the central nervous system in Characiformes. The study of brain gross morphology of 48 distinct taxa of Characiformes, one of Cypriniformes, two of Siluriformes and two of Gymnotiformes, allowed us to propose, for the first time, six putative brain synapomorphies for the Characiformes and also two possibly unique gross brain morphology characters for the Siluriformes. A detailed protocol for the extraction of the brain in Characiformes is also provided.

Gross morphology of the brain of Pseudopimelodus bufonius (Valenciennes, 1840) (Siluriformes: Pseudopimelodidae)

The gross morphology of the brain of the pseudopimelodid Pseudopimelodus bufonius is described and compared with congeners. Observations were made on removed brains after elimination of bones from the top of the skull and severing of the cranial nerves and the spinal cord. Nine morphometric characters associated with the major subdivisions of the brain were identified, seven of which revealed significant differences among the species examined. The corpus cerebelli in all examined species of the genus is the largest structure of the brain. The behavior of the species of Pseudopimelodus is still unknown, but in other teleosts that condition is typically correlated with a higher degree of motor coordination. Relative size proportions of the tectum opticum, eminentia granularis, lobus facialis and lobus vagi, might be related to carnivory and an enhanced capacity for food selection.

Phylogenetic analysis of molecular and morphological data highlights uncertainty in the relationships of fossil and living species of Elopomorpha (Actinopterygii: Teleostei)

Elopomorpha is one of the three main clades of living teleost fishes and includes a range of disparate lineages including eels, tarpons, bonefishes, and halosaurs. Elopomorphs were among the first groups of fishes investigated using Hennigian phylogenetic methods and continue to be the object of intense phylogenetic scrutiny due to their economic significance, diversity, and crucial evolutionary status as the sister group of all other teleosts. While portions of the phylogenetic backbone for Elopomorpha are consistent between studies, the relationships among Albula, Pterothrissus, Notacanthiformes, and Anguilliformes remain contentious and difficult to evaluate. This lack of phylogenetic resolution is problematic as fossil lineages are often described and placed taxonomically based on an assumed sister group relationship between Albula and Pterothrissus. In addition, phylogenetic studies using morphological data that sample elopomorph fossil lineages often do not include notacanthiform or anguilliform lineages, potentially introducing a bias toward interpreting fossils as members of the common stem of Pterothrissus and Albula. Here we provide a phylogenetic analysis of DNA sequences sampled from multiple nuclear genes that include representative taxa from Albula, Pterothrissus, Notacanthiformes and Anguilliformes. We integrate our molecular dataset with a morphological character matrix that spans both living and fossil elopomorph lineages. Our results reveal substantial uncertainty in the placement of Pterothrissus as well as all sampled fossil lineages, questioning the stability of the taxonomy of fossil Elopomorpha. However, despite topological uncertainty, our integration of fossil lineages into a Bayesian time calibrated framework provides divergence time estimates for the clade that are consistent with previously published age estimates based on the elopomorph fossil record and molecular estimates resulting from traditional node-dating methods.

Morphology of the jaw, suspensorial, and opercle musculature of Beloniformes and related species (Teleostei: Acanthopterygii), with a special reference to the m. adductor mandibulae complex

The taxon Beloniformes represents a heterogeneous group of teleost fishes that show an extraordinary diversity of jaw morphology. I present new anatomical descriptions of the jaw musculature in six selected beloniforms and four closely related species. A reduction of the external jaw adductor (A1) and a changed morphology of the intramandibular musculature were found in many Beloniformes. This might be correlated with the progressively reduced mobility of the upper and lower jaw bones. The needlefishes and sauries, which are characterised by extremely elongated and stiffened jaws, show several derived characters, which in combination enable the capture of fish at high velocity. The ricefishes are characterised by several derived and many plesiomorphic characters that make broad scale comparisons difficult. Soft tissue characters are highly diverse among hemiramphids and flying fishes reflecting the uncertainty about their phylogenetic position and interrelationship. The morphological findings presented herein may help to interpret future phylogenetic analyses using cranial musculature in Beloniformes.

Development of the splanchnocranium in Prochilodus argenteus (Teleostei: Characiformes) with a discussion of the basal developmental patterns in the Otophysi

Development of the mandibular, hyoid and gill arches, which constitute the splanchnocranium, are described for Prochilodus argenteus, order Characiformes, one of the basal lineages of the Otophysi. Development was examined from just hatched larvae through juveniles using whole specimens cleared and counterstained for cartilage and bone as well as histological preparations. Observations are compared with the developmental trends reported for Cypriniformes, the basalmost clade of the Otophysi. Shortened developmental sequences for Prochilodus compared to the cypriniform Catostomus were discovered in the ontogeny of the ceratohyals, ceratobranchials 1-5, epibranchials 1-4 and the symplectic portion of the hyosymplectic. Prochilodus also differs from Catostomus in having the basihyal plus the anterior copula appearing at different stages of ontogeny rather than simultaneously. Contrary to previous assumptions, developmental information indicates that hypobranchial 4 as well as likely basibranchial 5 are present in Prochilodus. Various developmental patterns in Prochilodus considered basal for the Otophysi, the predominant component of the Ostariophysi, are likely conserved from patterns prevalent in basal groups in the Actinopterygii.

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.