The pectoral anatomy of selected Ostariophysi. I. The Characiniformes.

The muscles and bones of the pectoral fin of Serrasalmus nattereri, the piranha, resemble those of generalized, lower teleosts with specializations related to a body shape adapted for high-speed carnivory; the pectoral fins being highly mobile with strong ligaments to the rays. The presence of two occipital nerves appears primitive, while the emergence of the subclavian artery within the branchial cavity, as in Gasteropelecus sternicla, appears specialized. The muscles and bones of the latter fish, a fresh-water flying fish, are specialized for self-propelled, aerial flight in the fusion of the right and left girdles greatly expanded for insertions of complex appendicular (flight) muscles, and in the consolidation of the rays and radials into one functional unit moving vertically in flight through contraction of vertical, massive ventral flight muscles. The bony pectoral anatomy of Electrophorus electricus, the electric eel, is specialized in having a mobile joint between the primary girdle and the cleithrum, the former being suspended vertically from the cleithrum by ligaments. The proximal radials and rays are very numerous and vertically aligned. The cleithrum is shaped to accommodate the extensive sternohyoid and pharyngocleithral muscles. The sheet-like appendicular muscles extend beyond the special joint and control its movement. The deeper muscles do not cross this joint. The arterial system is specialized in lacking a deep brachial artery.     

Description and scaling of pectoral muscles in ictalurid catfishes

The pectoral spine of catfishes is an antipredator adaptation that can be bound, locked, and rubbed against the cleithrum to produce stridulation sounds. We describe muscle morphology of the pectoral spines and rays in six species in four genera of North American ictalurid catfishes. Since homologies of catfish pectoral muscles have not been universally accepted, we designate them functionally as the spine abductor and adductor and the arrector dorsalis and ventralis. The four muscles of the remaining pectoral rays are the superficial and deep (profundal) abductors and adductors. The large spine abductor and spine adductor are responsible for large amplitude movements, and the smaller arrector dorsalis and arrector ventralis have more specialized functions, that is, spine elevation and depression, respectively, although they also contribute to spine abduction. Three of the four spine muscles were pennate (the abductor and two arrectors), the spine adductor can be pennate or parallel, and ray muscles have parallel fibers. Insertions of pectoral muscles are similar across species, but there is a shift of origins in some muscles, particularly of the superficial abductor of the pectoral rays, which assumes a midline position in Ictalurus and increasingly more lateral placement in Ameiurus (one quarter way out from the midline), and Pylodictis and Noturus (half way out). Coincident with this lateral shift, the attachments of the hypaxial muscle to the ventral girdle become more robust. Comparison with its sister group supports the midline position as basal and lateral migration as derived. The muscles of the pectoral spine are heavier than muscles of the remaining rays in all species but the flathead, supporting the importance of specialized spine functions above typical movement. Further, spine muscles were larger than ray muscles in all species but the flathead catfish, which lives in water with the fastest currents. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

The suction mechanism of the pipid frog,Pipa pipa (Linnaeus, 1758)

Most suction‐feeding, aquatic vertebrates create suction by rapidly enlarging the oral cavity and pharynx. Forceful enlargement of the pharynx is powered by longitudinal muscles that retract skeletal elements of the hyoid, more caudal branchial arches, and, in many fish, the pectoral girdle. This arrangement was thought to characterize all suction‐feeding vertebrates. However, it does not exist in the permanently aquatic, tongueless Pipa pipa , an Amazonian frog that can catch fish. Correlating high‐speed (250 and 500 fps) video records with anatomical analysis and functional tests shows that fundamental features of tetrapod body design are altered to allow P. pipa to suction‐feed. In P. pipa , the hyoid apparatus is not connected to the skull and is enclosed by the pectoral girdle. The major retractor of the hyoid apparatus arises not from the pectoral girdle but from the femur, which lies largely within the soft tissue boundaries of the trunk. Retraction of the hyoid is coupled with expansion of the anterior trunk, which occurs when the hypertrophied ventral pectoral elements are depressed and the urostyle and sacral vertebra are protracted and slide forward on the pelvic girdle, thereby elongating the entire trunk. We suggest that a single, robust pair of muscles adduct the cleithra to depress the ventral pectoral elements with force, while modified tail muscles slide the axial skeleton cranially on the pelvic girdle. Combined hyoid retraction, axial protraction, and pectoral depression expand the buccopharyngeal cavity to a volume potentially equal to that of the entire resting body of the frog. Pipa may be the only tetrapod vertebrate clade that enlarges its entire trunk during suction‐feeding.     

Anatomy and early development of the pectoral girdle,fin, and fin spine of sturgeons (Actinopterygii: Acipenseridae)

Acipenseriformes hold an important place in the evolutionary history of bony fishes. Given their phylogenetic position as extant basal Actinopterygii, it is generally held that a thorough understanding of their morphology will greatly contribute to the knowledge of the evolutionary history and the origin of diversity for the major osteichthyan clades. To this end, we examined comparative developmental series from the pectoral girdle in Acipenser fulvescens, A. medirostris, A. transmontanus, and Scaphirhynchus albus to document, describe, and compare ontogenetic and allometric differences in the pectoral girdle. We find, not surprisingly, broad congruence between taxa in the basic pattern of development of the dermal and chondral elements of the pectoral girdle. However, we also find clear differences in the details of structure and development among the species examined in the dermal elements, including the clavicle, cleithrum, supracleithrum, posttemporal, and pectoral‐fin spine. We also find differences in the internal fin elements such as the distal radials as well as in the number of fin rays and their association with the propterygium. Further, there are clear ontogenetic differences during development of the dermal and chondral elements in these species and allometric variation in the pectoral‐fin spine. The characters highlighted provide a suite of elements for further examination in studies of the phylogeny of sturgeons. Determining the distribution of these characters in other sturgeons may aid in further resolution of phylogenetic relationships, and these data highlight the role that ontogenetic and comparative developmental studies provide in systematics. J. Morphol. 276:241–260, 2015. © 2014 Wiley Periodicals, Inc.     

Raja koreana, a new species of skate (Elasmobranchii, Rajoidei) from Korea

A new rajid species,Raja koreana, is described from a single adult female specimen, 735 mm in total length, collected off the southwestern coast of the Korean Peninsula. AlthoughR. koreana is included in the group of species characterized by the scapulocoracoid lacking an anterior bridge and having the postventral fenestra expanded, it is unique among the latter in possessing: pectoral girdle propterygium not extending to snout tip; rostral shaft of neurocranium narrow and thick, unsegmented base with filamentous cartilage; snout fleshy; pores of ampullae of Lorenzini densely distributed over much of ventral surface to behind cloaca; most thorns on tail directed anteriorly; tail short; a pair of longitudinally elongated black blotches on middle of dorsal surface of disc when fresh; a pair of black blotches (grayish at center) posteriorly on pectoral fins; ventral surface of dise uniformly blackish-brown, except for areas around pores.     

REDUCTION OF THE PECTORAL SPINE AND GIRDLE IN DOMESTICATED CHANNEL CATFISH IS LIKELY CAUSED BY CHANGES IN SELECTION PRESSURE

Locked pectoral spines of the Channel Catfish Ictalurus punctatus more than double the fish's width and complicate ingestion by gape‐limited predators. The spine mates with the pectoral girdle, a robust structure that anchors the spine. This study demonstrates that both spine and girdle exhibit negative allometric growth and that pectoral spines and girdles are lighter in domesticated than in wild Channel Catfish. This finding could be explained by changes in selection pressure for spine growth during domestication or by an epigenetic effect in which exposure to predators in wild fish stimulates pectoral growth. We tested the epigenetic hypothesis by exposing domesticated Channel Catfish fingerlings to Largemouth Bass Micropterus salmoides predators for 13 weeks. Spines and girdles grow isometrically in the fingerlings, and regression analysis indicates no difference in proportional pectoral growth between control and predator‐exposed fish. Therefore a change in selection pressure likely accounts for smaller pectoral growth in domesticated Channel Catfish. Decreasing spine growth in older fish suggests anti‐predator functions are most important in smaller fish. Additionally, growth of the appendicular and axial skeleton is controlled differentially, and mechanical properties of the spine and not just its length are an important component of this defensive adaptation.     

On the osteology and myology of catfish pectoral girdle, with a reflection on catfish (Teleostei: Siluriformes) plesiomorphies

The configuration of the pectoral girdle bones and muscles of numerous catfishes was studied in detail and compared with that of other siluriforms, as well as of other teleosts, described in the literature. The pectoral girdle of catfishes is composed of only three bones, which probably correspond to the posttemporo-supracleithrum (posttemporal + supracleithrum), scapulo-coracoid (scapula + coracoid), and cleithrum of other teleosts. These latter two bones constitute the place of origin of the pectoral girdle muscles. Two of these muscles are related to the movements of the pectoral fin. These two muscles correspond, very likely, to the abductor superficialis and to the adductor superficialis of other teleostean fishes. In relation to the pectoral spine (thickened first pectoral fin ray), it is usually moved by three well-developed muscles, which are probably homologous with the arrector ventralis, arrector dorsalis, and abductor profundus of nonsiluriform teleosts. The morphological diversity and the plesiomorphic configuration of these muscles, as well as of the other catfish pectoral girdle structures, are discussed.     

The musculature of the papuan frog Phrynomantis stictogaster (Anura,Microhylidae)

The musculature of Phrynomantis stictogaster, a burrowing Papuan microhylid frog, of the subfamily Asterophryinae, is described and compared with accounts of other frogs. P. stictogaster exhibits unusual characters: dense musculature investing an entirely adherent tongue; exceptionally massive jaw musculature; and hitherto underscribed attachments of some muscles in the manus and pes. The presence of an accessory tendon to the M. glutaeus magnus and the pattern of distal thigh tendons confirm previous diagnosis of the Microhylidae, but the presence of an accessory head to M. adductor magnus is a condition previously not noted in the family. Features of the hyoid, pectoral, and thigh muscles resemble those of members of the subfamilies Dyscophinae, Microhylinae, and Spenophryninae.     

Bony‐toothed birds (Aves: Pelagornithidae) from the Middle Eocene of Belgium

Abstract: We describe well‐preserved remains of the Pelagornithidae (bony‐toothed birds) from the middle Eocene of Belgium, including a sternum, pectoral girdle bones and humeri of a single individual. The specimens are tentatively assigned to Macrodontopteryx oweni Harrison and Walker, 1976 , which has so far only been known from the holotype skull and a referred proximal ulna. Another species, about two times larger, is represented by an incomplete humerus and tentatively identified as Dasornis emuinus ( Bowerbank, 1854 ). The fossils provide critical new data on the osteology of the pectoral girdle of bony‐toothed birds. For the first time, the sternum of one of the smaller species is preserved, and this bone exhibits a more plesiomorphic morphology than the recently described sternum of the giant Miocene taxon Pelagornis. The coracoid resembles that of the Diomedeidae (albatrosses) in overall morphology, but because bony‐toothed birds lack apomorphies of the Procellariiformes, the similarities are almost certainly owing to convergence. Bony‐toothed birds were often compared with the ‘Pelecaniformes’ by previous authors, who especially made comparisons with the Sulidae (gannets and boobies). However, the coracoid distinctly differs from that of extant ‘pelecaniform’ birds, and the plesiomorphic presence of a foramen nervi supracoracoidei as well as the absence of a well‐delimited articulation facet for the furcula supports a position outside the Suloidea, the clade to which the Sulidae belong.     

How can ontogeny help us to understand the morphology of anuran pectoral girdle?

The ontogenetic development of the pectoral girdle in seven anuran species (Xenopus laevis, Discoglossus pictus, Bombina bombina, Bombina variegata, Pelobates fuscus, Bufo bufo and Rana dalmatina) was studied using cleared and stained specimens. The epicoracoid cartilage was found to develop in two different ways resulting in an arciferal or firmisternal type of the pectoral girdle. In the arciferal one, the epicoracoid originates from a medial prolongation of the procoracoid cartilage and broadly overlaps its counter part during further development. In the firmisternal pectoral girdle, the epicoracoids are formed by the widened cartilaginous medial edges of the coracoids that fuse together along the midline. Polarization of ontogenetic characters shows, that omosternum evolves inside Anura, and the type of sternum occurring in basal Anura seems to be an apomorphy of all Batrachia. The sternal elements have a single or paired rudiment, their development is connected with M. rectus abdominis or a zonal area and they remain cartilaginous or ossify during postmetamorphic development. An occurrence of omosternum in Barbourula busuangensis was described for the first time.     

A new Early Miocene genus of the family Sciaenidae (Teleostei, Perciformes) from the eastern Paratethys

A new genus of sciaenid fish Caucasisciaena is erected to accommodate the Early Miocene eastern Paratethys species Perca ignota Smirnov, 1936, which, subsequently, was variously attributed to the modern genera, either Larimus or Otolithoides. The materials examined include 32 specimens from four Caucasian and Crimean localities of Sakaraulian age (Lower Burdigalian). The new genus is based on a unique combination of features, including: parasphenoid with a dorsal rounded bony flange; basisphenoid present; premaxilla with short ascending process forming obtuse angle with alveolar process and ascending/alveolar process ratio about 0.17; anterior premaxillary teeth enlarged; posttemporal with few robust spines along its posterior margin; presence of 25 vertebrae; presence of three tiny supraneurals; dorsal fin with 11 spines plus 22–24 soft rays; anal fin with two spines and 7–8 soft rays; second anal-fin spine long and massive; pectoral fin elongate; scales ctenoid on body and cycloid on head (except for one or two rows of ctenoid scales on the cheek). Paleoecological considerations suggest that Caucasisciaena probably was a predatory fish that inhabited the coastal waters of the eastern sector of the Paratethyan basin.     

Cephalic muscle development in the Australian lungfish,Neoceratodus forsteri

Lungfishes are the extant sister group of tetrapods. As such, they are important for the study of evolutionary processes involved in the water to land transition of vertebrates. The evolution of a true neck, that is, the complete separation of the pectoral girdle from the cranium, is one of the most intriguing morphological transitions known among vertebrates. Other salient changes involve new adaptations for terrestrial feeding, which involves both the cranium and its associated musculature. Historically, the cranium has been extensively investigated, but the development of the cranial muscles much less so. Here, we present a detailed study of cephalic muscle development in the Australian lungfish, Neoceratodus forsteri, which is considered to be the sister taxon to all other extant lungfishes. Neoceratodus shows several developmental patterns previously described in other taxa; the tendency of muscles to develop from anterior to posterior, from their region of origin toward insertion, and from lateral to ventral/medial (outside‐in), at least in the branchial arches. The m.protractor pectoralis appears to develop as an extension of the most posterior m.levatores arcuum branchialium, supporting the hypothesis that the m.cucullaris and its derivatives (protractor pectoralis, levatores arcuum branchialium) are branchial muscles. We present a new hypothesis regarding the homology of the ventral branchial arch muscles (subarcualis recti and obliqui, transversi ventrales) in lungfishes and amphibians. Moreover, the morphology and development of the cephalic muscles confirms that extant lungfishes are neotenic and have been strongly influenced via paedomorphosis during their evolutionary history.     

The structure and function of the dermal pectoral girdle in bony fishes with particular reference to ostariophysines

The structure of the dermal pectoral girdle of teleostean fishes is analyzed in relation to its functions. In bony fishes the vertebral column, with a horizontal axis, and the pectoral girdle, with a basically vertical axis, form the only skeletal links between the head and the body. The individual bones of the dermal girdle are considered as supporting units joined by a series of articulations that permit differential movement between adjacent bones. The movements mediated by this linkage system are: lateral swinging of the head relative to the body, expansion of the distance between the central areas of the two pectoral girdles to permit passage of large food items, and fore-and-aft movements of the anteroventral ends of the cleithra relative to the skull. Among other factors affecting the structure of the dermal pectoral girdle are the provision for the support of the pectoral fin base and the requirement for the effective operation of a sleeve valve between the girdle and the opercular cover.
Modifications of the dermal pectoral girdle in ostariophysine fishes are discussed. A brief history of the bony fish girdle in terms of its functional components is postulated.     

The integument of the paddlefish,Polyodon spathula

The integument of the paddlefish (Polyodon spathula) is unusual as a relatively small amount of mucus is produced by epithelial cells that are not modified into regular mucous gland cells. A thick compact epidermis and dermis compensate for the slight amount of mucus secreted. Paddlefish have a variety of scales formed of concentric bony lamellae containing osteocytes. There are five kinds of scales: dorsal and ventral fulcra on the caudal fin, rhomboidal scales on the caudal lobe, horny denticles over the pectoral girdle, calcareous denticles on the trunk, and anchor-shaped plates on the rostrum. Except for the fulcra, the scales are undoubtedly vestigial. The numerous surface pits on the rostrum, head, operculum, and throat are epithelial invaginations which are not connected to lateral line canals. No nerves lead to the pits. The spherical to cuboidal and often ciliated cells at the base of the pits are considered to be aplasic cells of unformed neuromasts.     

Fossil fishes from china provide first evidence of dermal pelvic girdles in osteichthyans

Background

The pectoral and pelvic girdles support paired fins and limbs, and have transformed significantly in the diversification of gnathostomes or jawed vertebrates (including osteichthyans, chondrichthyans, acanthodians and placoderms). For instance, changes in the pectoral and pelvic girdles accompanied the transition of fins to limbs as some osteichthyans (a clade that contains the vast majority of vertebrates – bony fishes and tetrapods) ventured from aquatic to terrestrial environments. The fossil record shows that the pectoral girdles of early osteichthyans (e.g., Lophosteus, Andreolepis, Psarolepis and Guiyu) retained part of the primitive gnathostome pectoral girdle condition with spines and/or other dermal components. However, very little is known about the condition of the pelvic girdle in the earliest osteichthyans. Living osteichthyans, like chondrichthyans (cartilaginous fishes), have exclusively endoskeletal pelvic girdles, while dermal pelvic girdle components (plates and/or spines) have so far been found only in some extinct placoderms and acanthodians. Consequently, whether the pectoral and pelvic girdles are primitively similar in osteichthyans cannot be adequately evaluated, and phylogeny-based inferences regarding the primitive pelvic girdle condition in osteichthyans cannot be tested against available fossil evidence.

Methodology/Principal Findings

Here we report the first discovery of spine-bearing dermal pelvic girdles in early osteichthyans, based on a new articulated specimen of Guiyu oneiros from the Late Ludlow (Silurian) Kuanti Formation, Yunnan, as well as a re-examination of the previously described holotype. We also describe disarticulated pelvic girdles of Psarolepis romeri from the Lochkovian (Early Devonian) Xitun Formation, Yunnan, which resemble the previously reported pectoral girdles in having integrated dermal and endoskeletal components with polybasal fin articulation.

Conclusions/Significance

The new findings reveal hitherto unknown similarity in pectoral and pelvic girdles among early osteichthyans, and provide critical information for studying the evolution of pelvic girdles in osteichthyans and other gnathostomes.     

Description of Careproctus patagonicus sp. nov. and C. magellanicus sp. nov. (Pisces: Scorpaeniformes) from the lower slope of Drake Passage

Two new species of Liparidae are described from Drake Passage (55°32·8' S, 65°54·3' W). Careproctus patagonicus differs from all other congeneric species in the following combination of characters: C 9 (1+4/4), epural and parhypural unfused to single hypural; gill slit above P base; lower pectoral lobe well developed; pectoral girdle with one ventral radial (0+0+0+1) with a central foramen; da 2·4, aAf 10·2% LS; disk 41·5% HL; some crater-like pits on posterior half of body; head and anterior part of body white. Careproctus magellanicus has the following diagnostic characters: A 46; P 24, well-developed lower pectoral lobe; scattered crater-like spots and some thumb-tack prickles on body; one suprabranchial pore; basal plate of the pectoral girdle with two fenestrae; four radials (3+1), the first with a ventral notch; HL 17·1, preD 18·5% LS. The structure of the endochondral pectoral girdle of both species is commented.     

A new rheophilic South American darter (Crenuchidae: Characidium) from the rio Juruena basin,Brazil, with comments on morphological adaptations to life in fast-flowing waters

Characidium iaquira, a new species from the upper rio Juruena, rio Tapajós basin, Brazil, is described. The new species can be promptly distinguished from all congeners by having a unique v-shaped dark mark lying along the caudal-fin extension, in medium- and large-sized specimens, and a remarkable iridescent green colouration in life. Characidium iaquira is closely related to Characidium crandellii and Characidium declivirostre by sharing unambiguous synapomorphies such as branchiostegal membranes united to each other across the isthmus, a scaleless area extending from the isthmus to the pectoral girdle, and dermal flaps surrounding anterior and posterior naris independent, but touching each other distally. Morphological specializations of the paired fins in the three riffle-dwellers species are discussed, including the wing-like shape, robustness, and inclination of the pectoral fin.     

中国鲽形目鱼类骨骼的研究Ⅰ.肩带骨及腰带骨

本文比较了中国12属14种鲽形目鱼类的肩带骨及腰带骨,并参考了Ochiai(1963)有关日本钩嘴鳎等5属5种的研究;得知这些骨骼,特别是原始肩带骨与腰带骨,有退化趋势。这似因这些鱼类在向以体一侧侧卧,类似蝶泳姿势强化,偶鳍的功能逐渐变弱或消失,故支持偶鳍运动的这些骨骼也渐退化或消失。     

The role of the forelimb in prey capture in the Late Triassic reptile Megalancosaurus (Diapsida,Drepanosauromorpha)

The pectoral girdle and forelimb of the Late Triassic drepanosauromorph reptile Megalancosaurus are redescribed and their function reinterpreted. The whole skeleton of this diapsid is highly specialised for arboreal life, and also the peculiarities of the shoulder girdle and forelimb were interpreted as adaptations for a limb-based locomotion using gap-bridging to move from one support to another, as in chameleons. Re-examination of the pectoral girdle and forelimb revealed the presence of clavicles fused into a furcula-like structure, a saddle-shaped glenoid and a tight connection between the radius and ulna that strengthened the forearm but hindered pronation and supination movements at that joint. The new information plus a reconstruction of the pectoral and forelimb musculature suggests that the forelimb was also specialised for grasping and raking in addition to climbing and thus prey capture may have been an important function for the forelimb. The new functional interpretation fits well with the overall body architecture of Megalancosaurus’ skeleton, suggesting that this reptile was an ambush predator that may have assumed a stable tripodal position, secured by the hooked tail and hind limbs, freeing its forelimbs to catch prey by sudden extension of the arm and firm grasping with the pincer-like digits.