Hyobranchial Apparatus Research Articles

The anatomy and feeding mechanism of the Japanese giant salamander (Andrias japonicus).

The fully aquatic Japanese giant salamander (Andrias japonicus) is a member of the Cryptobranchidae, and is currently distributed in western Japan, with other members of this group restricted to China and North America. Their feeding behaviour is characterized by a form of suction feeding that includes asymmetric movements of the jaw and hyobranchial apparatus. Previous studies on the North American species, Cryptobranchus alleganiensis, have suggested that this specialized jaw movement is produced by a flexible quadrate-articular joint combined with a loosely connected lower jaw symphysis including two small fibrocartilaginous pads. However, little is known about this feeding behaviour in the Asian species, nor have the three-dimensional asymmetric jaw movements been fully investigated in any member of Cryptobranchidae. In this study, we explore the asymmetric jaw movements in A. japonicus using three methods: (1) dissection of musculoskeletal structures; (2) filming of feeding behaviour to understand in which situations asymmetric feeding is used; (3) analysis of 3D movement of jaws and skull. In the third component, fresh (from frozen) specimens of A. japonicus were manipulated to replicate asymmetric and symmetric jaw movements, with the specimens CT scanned after each step to obtain the 3D morphology of the jaws at different positions. These positions were combined and their Euler angles from resting (closed) jaw position were calculated for asymmetric or symmetric jaw positions. Our filming revealed that asymmetric jaw movements are linked to the position of the prey in relation to the snout, with the jaw closest to the prey opening asymmetrically. Moreover, this action allows the salamander to simultaneously grasp prey in one side of the mouth while ejecting water on the other side, if the first suction attempt fails. The asymmetric jaw movements are performed mainly by rotation of the mandible about its long axis, with very limited lateral jaw movements. During asymmetric and symmetric jaw movements, the posterior ends of the maxilla and quadrate move slightly. The asymmetric jaw movements are permitted by a mobile quadrate-articular joint formed by wide, round cartilages, and by two small fibrocartilage pads within the jaw symphysis that act as cushions during jaw rotation. Some of these soft tissue structures leave traces on the jaws and skull, allowing feeding mode to be reconstructed in fossil taxa. Understanding cryptobranchid asymmetric jaw movement thus requires a comprehensive assessment of not only the symphysial morphology but also that of other cranial and hyobranchial elements.

The exceptionally well-preserved Sauropleura scalaris (Nectridea: Urocordylidae) from the late Carboniferous of the Czech Republic: new information on ontogeny, lateral line and tail

Abstract Urocordylids represent a group of the late Carboniferous–early Permian basal tetrapods, with short limbs, extremely elongated bodies and a deep and distinctive tail and vertebral architecture, which is indicative of an aquatic habitat. However, the important morphological structures that would indicate their ecological preferences unambiguously (e.g. hyobranchial apparatus, lateral line sulci) remain unknown. Moreover, the high degree of skeletal ossification present in urocordylids contrasts with the common pattern seen in most other basal tetrapods known to inhabit aquatic environments. Here, we describe an exceptionally well-preserved skull, with an associated mandible and a partial postcranial skeleton, of Sauropleura scalaris from the locality of Nýřany, Czech Republic, based on high-resolution micro-computed tomography. The labial surface of the mandible shows the first evidence of the lateral line system in Urocordylidae, which consists of both small pits and elongated grooves, and unambiguously supports the aquatic ecology of the group. The juvenile stage of the specimen provides new information on ontogeny of sauropleurines. The partly ossified opisthotic bone indicates that, unlike development in most other early tetrapods, the otic capsules were among the first neurocranial elements to ossify in nectrideans. Finally, an almost complete caudal region suggests that tails were much longer in sauropleurines than previously assumed.

The larval brachyopid Platycepsion wilkinsoni from the Triassic of New South Wales provides insight into the stereospondyl life cycle

AbstractThe small, immature brachyopid stereospondyl Platycepsion wilkinsoni from the Early or Middle Triassic of Gosford, New South Wales, is redescribed from a developmental point of view. Whereas the sutural contact between postorbital and parietal suggested by earlier authors cannot be confirmed, a new autapomorphy, the posterior process of the interclavicle with a slightly concave posterior margin, is recognized. A further apomorphic state may be the probable presence of five pairs of ossified ceratobranchials. Soft-tissue preservation of external gills demonstrates that Platycepsion wilkinsoni represents a true larva, forming the first evidence of a larval stage in stereospondyls. Morphology and developmental stage of Platycepsion wilkinsoni indicates that brachyopids conserved the plesiomorphic ontogenetic pattern seen in most Paleozoic temnospondyls, including the early ossification of the dermal skull roof and delayed ossification of the postcranium. The strongly developed ornament, the widened lateral lines, and the well-ossified exoccipitals and stapes suggest an even faster ossification and differentiation of the skull compared to Paleozoic temnospondyls and might represent a general stereospondyl characteristic. In the vertebral column, only the poorly differentiated, still separate neural arches are ossified, whereas the centra remained cartilaginous. This implies that the plesiomorphic pattern of vertebral development was conserved in Mesozoic stereospondyls, irrespective of whether the adult vertebral morphology was rhachitomous, stereospondylous, or diplospondylous. The low degree of ossification of the postcranium, its slow differentiation, and the delayed development of the scapulocoracoid indicate an aquatic mode of life, and the strongly ossified skull and hyobranchial apparatus suggest an emphasis on powerful suction feeding.

Larval morphology of three syntopic species of emKaloula/em Gray (Anura: Microhylidae) from Vietnam.

The external larval morphology of three species of the microhylid genus Kaloula (K. indochinensis, K. mediolineata, and K. pulchra) inhabiting the southern and central regions of Vietnam is studied. The similarities and the distinctive features of their morphometric characters, the structure of their mouthparts and spiracle, and their coloration are analysed with consideration of the geographic variability. A description of the tadpole of K. indochinensis is provided for the first time. The interspecific comparison revealed the shape of the mouthparts and the spiracle as the most reliable diagnostic characters for the field identification of the coexistent Kaloula tadpoles. The first description of the larval chondrocranium and hyobranchial apparatus of K. indochinensis demonstrates a set of morphological traits characteristic of suspension-feeding microhylids. Some developmental parameters (egg number and size, duration of embryonic and larval development, larvae size and stage at hatching) are provided for K. indochinensis and K. pulchra.

A survey of the external morphology, internal oral morphology, chondrocranium and hyobranchial apparatus of Elachistocleis larvae Parker, 1927 (Anura, Microhylidae).

The external morphology, internal oral morphology, the chondrocranium and the hyobranchial apparatus of Elachistocleis bumbameuboi, E. cf. piauiensis, E. cesarii and E. bicolor are described and compared with each other and with other species of microhylids using available descriptions from the literature. The general morphology of Elachistocleis species is conservative in many aspects. Differences between species are subtle and are found in the body shape, the edge of the snout, fin height, if the lateral line is evident, the presence of regular pustules in the buccal roof arena, the posterolateral edge of the cartilago suprarostralis, the shape of the fenestra in the occipital region, presence or absence of fenestra hypophysea, the margin of the processus antorbitalis, expansions in the ventrolateral process, the shape and inclination of the fenestra subocularis, whether the subotic process is single or slightly bifid, and the inclination of the processus anterolateralis hyalis.

Ontogenetic plasticity in cranial morphology is associated with a change in the food processing behavior in Alpine newts

BackgroundThe feeding apparatus of salamanders consists mainly of the cranium, mandible, teeth, hyobranchial apparatus and the muscles of the cranial region. The morphology of the feeding apparatus in turn determines the boundary conditions for possible food processing (i.e., intraoral mechanical reduction) mechanisms. However, the morphology of the feeding apparatus changes substantially during metamorphosis, prompting the hypothesis that larvae might use a different food processing mechanism than post-metamorphic adults. Salamandrid newts with facultative metamorphosis are suitable for testing this hypothesis as adults with divergent feeding apparatus morphologies often coexist in the same population, share similar body sizes, and feed on overlapping prey spectra.MethodsWe use high-speed videography to quantify the in vivo movements of key anatomical elements during food processing in paedomorphic and metamorphic Alpine newts (Ichthyosaura alpestris). Additionally, we use micro-computed tomography (μCT) to analyze morphological differences in the feeding apparatus of paedomorphic and metamorphic Alpine newts and sort them into late-larval, mid-metamorphic and post-metamorphic morphotypes.ResultsLate-larval, mid-metamorphic and post-metamorphic individuals exhibited clear morphological differences in their feeding apparatus. Regardless of the paedomorphic state being externally evident, paedomorphic specimens can conceal different morphotypes (i.e., late-larval and mid-metamorphic morphotypes). Though feeding on the same prey under the same (aquatic) condition, food processing kinematics differed between late-larval, mid-metamorphic and post-metamorphic morphotypes.ConclusionsThe food processing mechanism in the Alpine newt changes along with morphology of the feeding apparatus during ontogeny, from a mandible-based to a tongue-based processing mechanism as the changing morphology of the mandible prevents chewing and the tongue allows enhanced protraction. These results could indicate that early tetrapods, in analogy to salamanders, may have developed new feeding mechanisms in their aquatic environment and that these functional innovations may have later paved the way for terrestrial feeding mechanisms.

The Larva and Advertisement Call of Bokermannohyla ahenea (Anura: Hylidae)

Bokermannohyla ahenea is endemic to the Serra da Bocaina, a portion of the Serra do Mar in the Atlantic Forest of Southeastern Brazil. Little information is currently available about this species. Herein, we describe the larval morphology of B. ahenea, including internal oral features, chondrocranium, and hyobranchial apparatus, along with its advertisement call and natural history notes. This is the first description of the chondrocranium and hyobranchial apparatus for a member of the genus Bokermannohyla. The larval external morphology of B. ahenea is similar to those of other species of the B. circumdata group, but it can be distinguished from those of other species of the genus by its oral apparatus. The advertisement call of B. ahenea is complex with many numbers of notes. Also, spectral and temporal parameters of the advertisement call can be used to distinguish B. ahenea from its congeners.

Development of the chondrocranium of two caiman species, Caiman latirostris and Caiman yacare.

Little is known about the embryonic development and variation of the chondrocranium in Crocodylia and there are no works on any Caiman species. Due to the importance of cranial features in the systematics of this clade, investigating the development of the skull in embryonic stages is essential. In this study, we present for the first time the development of the cartilaginous skull of two extant Caiman species. Anatomical descriptions of the embryonic chondrocranium of Caiman latirostris and Caimanyacare were made, paying special attention to their inter- and intraspecific variation. For this purpose, pre-hatching ontogenetic cranial series of these two caiman species were prepared with a double staining and diaphanization technique. The main differences with other crocodylian species were observed in the palatoquadrate, and interspecific variation within the genus was recorded in the hyobranchial apparatus and larynx. Some characters may be distinctive of Caiman (posterior and ventral surface of the otic process of the palatoquadrate articulated with the dorsal process of the columella auris, and otic process articulated with the lateral wall of the auditory capsule), Alligatoridae (presence of an epiphanial foramen) or C. latirostris and C.yacare (Corpus hyoidei with different number and position of foramina and different shapes of its anterior contour and anterior and posterior notch, different degrees of broadening of the distal end of the Cornu branchiale I, and presence/absence of a notch in the posteroventral surface of the cricoid). Homologies of the elements belonging to the hyobranchial apparatus could not be confirmed. As in other tetrapods the trachea consists of incomplete cartilaginous rings. Morphological changes and dissimilarities found in this study are useful as a context to start studying phylogenetic constraints. Moreover, in a heterochronic context, variations may be involved.

The larvae of two species of Bokermannohyla (Anura, Hylidae, Cophomantini) endemic to the highlands of central Brazil.

Bokermannohyla (tribe Cophomantini) is an endemic genus of Brazilian treefrogs containing 32 species arranged into four phenetic groups. The B. pseudopseudis group includes nine species, which are typically found in rupestrian ecosystems of disjunct Brazilian mountain ranges. Tadpoles have been shown to be important sources of information for the taxonomy of this genus, although careful analyses of character variation and descriptions of internal anatomy remain scarce. Since the first description of B. pseudopseudis tadpoles was based on a mixed series containing specimens of B. pseudopseudis and B. sapiranga, we describe the larvae of these two species from their type localities, including their external morphology, oral cavity, and skeletal system. Tadpoles of B. pseudopseudis are easily distinguished from those of B. sapiranga by aspects of their coloration and characters of their oral disc (more labial tooth rows, more numerous submarginal papillae and flaps with labial teeth). These morphological differences may be diagnostic for these two similar species, whereas their chondrocranium, hyobranchial apparatus, and oral cavity are alike, suggesting less variability in these character systems between closely related species. Finally, we provide the first comparison of data on the skeletal system of Bokermannohyla and other Cophomantini, highlighting characters of potential relevance to the systematics of the tribe.

Ontogeny, But Not Sexual Dimorphism, Drives the Intraspecific Variation of Quadrate Morphology in Hemidactylus turcicus (Squamata: Gekkonidae)

Abstract The functional components of the lizard skull are divided into the chondrocranial braincase, protective dermatocranium, lower jaw, and hyobranchial apparatus. These regions are interconnected and become operational through the quadrate, a bone critical for cranial biomechanics and support of the peripheral auditory system. The quadrate is a complex and variable structure in squamates; however, neither the intraspecific nor interspecific variation of this element has been studied in detail. We investigated the intraspecific variation of quadrate morphology within Hemidactylus turcicus with the use of cleared and double-stained specimens and high-resolution x-ray microcomputed tomography. Our objectives were to quantify quadrate shape and the degree of intraspecific variation within this element with the use of 2-D and 3-D geometric morphometric analyses and investigate if this variation is driven by ontogeny and/or sexual dimorphism. Our results demonstrate that ontogeny, but not sexual shape dimo...

Functional morphology of terrestrial prey capture in salamandrid salamanders.

Salamanders use the hyobranchial apparatus and its associated musculature for tongue projection on land and for suction feeding in water. Hyobranchial apparatus composition and morphology vary across species, and different morphologies are better suited for feeding in aquatic versus terrestrial environments. We hypothesize that differences in hyobranchial morphology result in functional trade-offs in feeding performance. We predict that semi-aquatic and aquatic salamandrids with hyobranchial morphology suited for aquatic feeding will have lower performance, in terms of tongue-projection distance, velocity, acceleration and power, compared with terrestrial salamandrids when feeding in a terrestrial environment. We found that semi-aquatic and aquatic newts had lower velocity, acceleration and muscle-mass-specific power of tongue projection when compared with the terrestrial salamanders Chioglossa lusitanica and Salamandra salamandra The fully aquatic newt, Paramesotriton labiatus, has a robust, heavily mineralized hyobranchial apparatus and was unable to project its tongue during terrestrial feeding, and instead exhibited suction-feeding movements better suited for aquatic feeding. Conversely, terrestrial species have slender, cartilaginous hyobranchial apparatus and enlarged tongue pads that coincided with greater tongue-projection distance, velocity, acceleration and power. Chioglossalusitanica exhibited extreme tongue-projection performance, similar to that seen in elastically projecting plethodontid salamanders; muscle-mass-specific power of tongue projection exceeded 2200 W kg-1, more than 350 times that of the next highest performer, Ssalamandra, which reached 6.3 W kg-1 These findings reveal that two fully terrestrial salamandrids have morphological specializations that yield greater tongue-projection performance compared with species that naturally feed in both aquatic and terrestrial environments.

Functional trade-offs in the aquatic feeding performance of salamanders

During aquatic feeding salamanders use the hyobranchial apparatus to capture prey. The hyobranchial apparatus depresses the floor of the mouth, effectively expanding the oropharyngeal cavity and generating suction. Within the family Salamandridae, there is a wide range of ecological diversity, with salamanders being terrestrial, semi-aquatic, or aquatic as adults. The purpose of this research was to quantify the diverse morphology and suction feeding performance of aquatically feeding salamandrids. We hypothesized that a more robust hyobranchial apparatus morphology would yield increased aquatic feeding performance. When compared to semi-aquatic newts, the fully aquatic species Paramesotriton labiatus had greater mineralization of the hyobranchial apparatus, as well as relatively more narrow basibranchial and wider ceratobranchial I+II complexes. These morphological differences coincide with greater aquatic feeding performance. Kinematics from high-speed videography revealed that maximum mouth opening velocity and acceleration were approximately two and five times greater, respectively, in Paramesotriton, and hyobranchial depression acceleration was found to be approximately three times greater than in the semi-aquatic species Pleurodeles waltl, Notophthalmus viridescens, Triturus dobrogicus, and Cynops cyanurus. Using digital particle image velocimetry, peak and average fluid velocity generated in Paramesotriton during suction feeding events were found to be 0.5ms−1 and 0.2ms−1, respectively, doubling that of all semi-aquatic species. These findings reveal that specialized morphology increases aquatic feeding performance in a fully aquatic newt.

Morphology and development of the hyolaryngeal apparatus of Pipa arrabali (Anura: Pipidae)

Two different perspectives guide ontogenetic studies. On one hand, there is a concern with objective processes and the understanding of the underlying mechanisms that governed the appearance of morphological differences between taxa; on the other hand, there are similarities between ontogenetic patterns that are used as phylogenetic characters. One focus of ontogenetic studies is to understand how morphology and timing of development differ among species. Such studies also aim to serve as a guide in proposing hypotheses of homology, especially when extremely modified structures are under scrutiny, such as the hyobranchial apparatus of amphibians. Here, we describe the morphology and development of the hyobranchial apparatus of Pipa arrabali (based on the examination of 51 embryos and six newly hatched specimens). Its morphology is compared to that described in the literature for other species. In P. arrabali, Copula I is absent, Copula II is present, and the ceratobranchials are simple, without spines or cartilaginous rays. In general, the ontogeny of the hyobranchial apparatus of P. arrabali seems to be accelerated when compared with that of other frogs, with some stages being skipped and the absence of some tadpole-specific structures observed in other species of pipids and non-pipids.

The Skull of Phyllomedusa sauvagii (Anura, Hylidae).

The hylid genus Phyllomedusa comprises charismatic frogs commonly known as monkey, leaf or green frogs, and is the most diverse genus of the subfamily Phyllomedusinae, including about 31 species. Although there is some information about the anatomy of these frogs, little is known about the osteology. Here the adult skull of Phyllomedusa sauvagii, both articulated and disarticulated, is described and the intraspecific variation is reported. Additionally, cartilage associated with the adult skull, such as the nasal capsules, auditory apparatus, and hyobranchial apparatus, are included in the analysis. Further examination of disarticulated bones reveals their remarkable complexity, specifically in the sphenethmoid and of the oocipital region. The description of disarticulated bones is useful for the identification of fossil remains as well as providing morphological characteristics that are phylogenetically informative. When comparing the skull morphology with the available information of other species of the genus, Phyllomesusa sauvagii skull resembles more that of P. vaillantii and P. venusta than P. atelopoides.

A complex hyobranchial apparatus in a Cretaceous dinosaur and the antiquity of avian paraglossalia

The highly specialized feeding apparatus of modern birds is characterized in part by paraglossalia, triangular bones or cartilages in the tongue that constitute part of the rarely fossilized hyobranchial apparatus. Here, we report on a new, juvenile specimen of the ankylosaurid dinosaur Pinacosaurus grangeri Gilmore, 1933 that provides the first evidence of paraglossalia outside of crown group Aves. The specimen is remarkable in preserving a well-ossified hyobranchial apparatus, including paired paraglossalia, first and second ceratobranchials, epibranchials, and evidence of a median cartilaginous basihyal. Reassessment of Edmontonia, another ankylosaur, also reveals evidence of bony paraglossalia. Ankylosaur paraglossalia closely resemble those of birds, but are relatively larger and bear prominent muscle scars, supporting the hypothesis that ankylosaurs had fleshy, muscular tongues. The other hyobranchial elements, surprisingly, resemble those of terrestrially feeding salamanders. Ankylosaurs had reduced, slowly replacing teeth, as evidenced from dental histology, suggesting that they relied greatly on their tongues and hyobranchia for feeding. Some curved, rod-like elements of other dinosaur hyobranchia are reinterpreted as second ceratobranchials, rather than first ceratobranchials as commonly construed. Ankylosaurs provide rare fossil evidence of deep homology in vertebrate branchial arches and expose severe biases against the preservation and collection of the hyobranchial apparatus. In light of these biases, we hypothesize that paraglossalia were present in the common ancestor of Dinosauria, indicating that some structures of the highly derived avian feeding apparatus were in place by the Triassic Period.

New insight into the anatomy of the hyolingual apparatus of Alligator mississippiensis and implications for reconstructing feeding in extinct archosaurs.

Anatomical studies of the cranium of crocodilians motivated by an interest in its function in feeding largely focused on bite force, the jaw apparatus and associated muscles innervated by the trigeminal nerve. However, the ossified and cartilaginous elements of the hyoid and the associated hyolingual muscles, innervated by the facial, hypoglossal and glossopharyngeal nerves, received much less attention. Crocodilians are known to retain what are ancestrally the 'Rhythmic Hyobranchial Behaviors' such as buccal oscillation, but show diminished freedom and movement for the hyobranchial apparatus and the tongue in food transport and manipulation. Feeding among crocodilians, generally on larger prey items than other reptilian outgroups, involves passive transport of the food within the mouth. The tongue in extant crocodilians is firmly attached to the buccal floor and shows little movement during feeding. Here, we present a detailed anatomical description of the myology of the hyolingual apparatus of Alligator mississippiensis, utilizing contrast-enhanced micro-computed tomography and dissection. We construct the first three-dimensional (3D) description of hyolingual myology in Alligator mississippiensis and discuss the detailed implications of these data for our understanding of hyolingual muscle homology across Reptilia. These anatomical data and an evaluation of the fossil record of hyoid structures also shed light on the evolution of feeding in Reptilia. Simplification of the hyoid occurs early in the evolution of archosaurs. A hyoid with only one pair of ceratobranchials and a weakly ossified or cartilaginous midline basihyal is ancestral to Archosauriformes. The comparison with non-archosaurian reptilian outgroup demonstrates that loss of the second set of ceratobranchials as well as reduced ossification in basihyal occurred prior to the origin of crown-clade archosaurs, crocodilians and birds. Early modification in feeding ecology appears to characterize the early evolution of the clade. Hyoid simplification has been linked to ingestion of large prey items, and this shift in hyoid-related feeding ecology may occur in early archosauriform evolution. A second transformation in hyoid morphology occurs within the crocodilian stem lineage after the split from birds. In Crocodyliformes, deflections in the ceratobrachials become more pronounced. The morphology of the hyoid in Archosauriformes indicates that aspects of the hyolingual apparatus in extant crocodilians are derived, including a strong deflection near the midpoint of the ceratobranchials, and their condition should not be treated as ancestral for Archosauria.

Gross morphology and topographical relationships of the hyobranchial apparatus and laryngeal cartilages in the ostrich (Struthio camelus)

AbstractThe ostrich hyobranchial apparatus consists of the centrally positioned paraglossalia and basiurohyale and paired caudo‐lateral elements (horns), each consisting of the ceratobranchiale and epibranchiale. The paraglossalia lie within the tongue parenchyma and consist of paired, flat, caudo‐laterally directed cartilages joined rostrally. The basiurohyale forms a single dorso‐ventrally flattened unit composed of an octagonal‐shaped body from which extend rostral (the rostral process) and caudal (the urohyale) projections. The laryngeal skeleton consists of cricoid, procricoid and paired arytenoid cartilages. The large ring‐shaped cricoid cartilage displays a body and paired wings which articulate with each other and with the procricoid. The blunt, ossified, rostral projection of the cricoid and the scalloped nature of the arytenoid cartilages are unique to the ostrich. The procricoid is a single structure which links the paired arytenoids and wings of the cricoid. The hyobranchial apparatus is firmly attached to the tongue parenchyma and to the larynx and proximal trachea. In contrast to previous reports in this species, the horns of the hyobranchial apparatus are not related to the skull. Ossification of the body of the basihyale, the ceratobranchials and the rostral process and body of the cricoid cartilage of the larynx lends stability to these structures.

Description of the previously unknown tadpole of <i>Hyalinobatrachium pulveratum</i> (Anura: Centrolenidae)

Egg clutches of the centrolenid Hyalinobatrachium pulveratum were sampled in four lowland locations of Costa Rica. The ontogenesis of the tadpoles of this species is documented by periodical descriptions of the larval stages. Larvae of H. pulveratum change their shape during development because of the non-equal growth of some body parts. Due to these changes the larvae in early stages of development differ considerably to those from later stages. Young larvae have a nearly circular cross-section, whereas later larval stages change to a typical flat shape. Some further morphological characteristics like width of the interorbital distance and the oral disk width change but not proportional to larvae length. Numerous measurements on different larval sizes help to recognize the larvae of H. pulveratum in all stages. The striking bright red hyobranchial sinus is the conspicuous characteristic feature ventrally of the hyobranchial apparatus. The use of allometric values for taxonomic and ontogenetic studies is discussed.

Nasal cartilages, hyobranchial apparatus, larynx, and glottal tubes in four species of Hydropsini (Serpentes: Dipsadidae: Xenodontinae)

Tribe Hydropsini (Serpentes: Dipsadidae: Xenodontinae) consists of three genera of aquatic snakes, Helicops, Hydrops, and Pseudoeryx, in which cartilaginous cranial features have been poorly studied. We here describe the nasal cartilages, hyobranchial apparatus, larynx, and glottal tubes in four representative Hydropsini species, compare them with species from other Dipsadidae tribes, and discuss our results in the context of the adaptation to the aquatic and fossorial habit. The studied species possess two nasal features that deviate from the pattern of nasal cartilages known in other aletinophidian and caenophidian snakes: (1) a cartilaginous connection between the lamina transversalis anterior and the concha of the Jacobson´s organ, and (2) a small rostral projection of the planum anteorbitale, which probably represents a reduced anterior maxillary process. Two putative synapomorphic features may be supporting the monophyly of Hydropsini: (1) a short inferior median eminence of the cricoid cartilage, and (2) a large processus entoglossus of the hyobranchial apparatus. The second feature also occurs in other snakes, such as the aquatic Farancia abacura (Dipsadidae: incertae sedis), the semi-fossorial Oxyrhopus rhombifer (Xenodontinae: Pseudoboini), and the fossorial Phalotris bilineatus (Xenodontinae: Elapomorphini). This feature may represent a convergent cranial adaptation between aquatic and fossorial snakes. Similarly, the short inferior median eminence of the cricoid cartilage, which also occurs in Farancia abacura, may represent a convergent adaptation to the fully aquatic habit in these species.

Extreme tadpoles II: the highly derived larval anatomy of Occidozyga baluensis (Boulenger, 1896), an obligate carnivorous tadpole

Tadpoles of Occidozyga species have been reported to be carnivorous, feeding on insects and other tadpoles. We present photographic evidence for the previously undocumented larval feeding behavior in O. baluensis. Furthermore, we present a detailed anatomical description of the skull, cranial musculature, and gross gut morphology based on three-dimensional reconstructions from serial sections and μCT imagery. The cranial anatomy of larval O. baluensis is highly derived in many characters, with respect to taxa outside the genus Occidozyga, most notably the palatoquadrate and hyobranchial apparatus, that play a major role in tadpole feeding. A large larval stomach was present in the specimens examined, indicative of a macrophagous carnivorous mode of feeding. Because of the relatively small oral orifice, relatively large-sized food items found in the larval stomach, and the tunnel-like arrangement of structures that form the buccal cavity, we hypothesize that suction feeding utilizing strong negative pressure is employed by this species. Furthermore, we propose that force, rather than speed, is the main characteristic of their feeding. The unique features of the study species substantially expand the known morphospace for tadpoles, particularly among the Acosmanura (Pelobatoidea, Pelodytoidea, and Neobatrachia). Except for Microhylidae, acosmanurans previously described possess limited innovative larval morphologies. Larval carnivory has evolved convergently several times in distant anuran clades and shows structural, behavioral, and functional differences in the known examples.