Ecomorphology of the digestive tract of the brazilian electric ray Narcine brasiliensis (Olfers, 1831) (Torpediniformes: Narcinidae)

Elasmobranchii shows particular characteristics that make them susceptible to the impacts caused by fishing pressure, especially bottom trawling, which mostly affect rays, as they have demersal habits. Based on food availability and feeding ability, Polychaeta and Sipunculiforme are the bases of Brazilian electric ray Narcine brasiliensis diet. Morphologically, the digestion starts in the oesophagus with acid mucines action. The existence of acid and neutral mucines in the posterior intestine prevents lesions in the mucosa and favours the passage of faeces and shell residues. Thus, this study shows the interaction between their habitat, the organisms and their morphophysiology.     

Influence of estuarine and continental shelf water advection on the coastal movements of apron ray Discopyge tschudii in the Southwestern Atlantic

Evaluated was the seasonal and inter‐annual association between habitat variables and distribution pattern of the apron ray (Discopyge tschudii) and its relationship, with the main force on the environmental condition to understand the influence of estuarine and continental shelf processes in the coastal fishes of the Southwestern Atlantic Coastal System (34°–41°S). Two winter and five spring research surveys in the SACS were analyzed and the Perry and Smith methodology applied to determine the seasonal association of depth, temperature and salinity and the abundance of apron ray. The season with the highest inter‐annual spatial distribution variation was related to the main external force on environmental conditions (e.g. wind, atmospheric temperature, and Río de la Plata discharge and shelf water intrusion). Apron ray showed persistent habitat selection, with the water temperature (<16°C) and salinity (higher than 31.8) being environmental factors most influencing its spatial distribution. In the spring, the apron ray spatial distribution showed higher inter‐annual variation than in winter. The persistence of the spring habitat selection of D. tschudii suggests that its onshore‐offshore as well as north‐south movements are influenced by water mass movements forced by a combination of local conditions (wind) and regional‐scale weather patterns (e.g. strength of the Malvinas Current). This study provides evidence on the importance of considering environmental conditions on the spatial distribution of apron ray and improves the knowledge on interactions between estuarine and shelf water dynamics as determinants of the spatial distribution of a coastal fish species in the Southwest Atlantic Coastal System.     

Microstructural morphology in early dermal denticles of hammerhead sharks (Elasmobranchii: Sphyrnidae) and related taxa

Mello, W.C., de Carvalho, J.J., Brito, P.M.M. 2011. Microstructural morphology in early dermal denticles of hammerhead sharks (Elasmobranchii: Sphyrnidae) and related taxa. —Acta Zoologica (Stockholm) 00 : 1–7. This study uses scanning electron microscopies to investigate and describe the microstructural diversity of dermal denticles in the family Sphyrnidae, which comprises all living hammerhead shark species, comparing them to other related taxa (i.e. Carcharhinus dussumieri, Carcharhinus plumbeus, Carcharhinus acronotus, Rhizoprionodon acutus, Negaprion brevirostris and Hemigaleus microstoma). The results reveal that sphyrnids present noticeable microstructures in the dermal denticles, distinguishing them from the other related species investigated. Additionally, scale patterns are the same in three distinct body regions (i.e. cephalic, branchial and dorsal fin). Species of Sphyrnidae that reach bigger total lengths and that are widely distributed (i.e. Sphyrna lewini and Sphyrna mokarran) presented more, smaller and nearly hexagonal microstructures that do not cover the entire scale surface, unlike species reaching smaller sizes and restricted to coastal habits (i.e. Sphyrna tiburo, Sphyrna tudes, Sphyrna media and Eusphyra blochii). The sphyrnid scales are similar to R. acutus and C. dussumieri rather than to the other species, but it is not possible to identify the sphyrnid species only by scale features. It is clear that a similar morphology of scales is not necessarily related to similar life habits, and that they are candidates to provide new characters in phylogenetical studies among sphyrnids.     

Dental homologies in lamniform sharks (Chondrichthyes: Elasmobranchii).

The dentitions of lamniform sharks are said to exhibit a unique heterodonty called the "lamnoid tooth pattern." The presence of an inflated hollow "dental bulla" on each jaw cartilage allows the recognition of homologous teeth across most modern macrophagous lamniforms based on topographic correspondence through the "similarity test." In most macrophagous lamniforms, three tooth rows are supported by the upper dental bulla: two rows of large anterior teeth followed by a row of small intermediate teeth. The lower tooth row occluding between the two rows of upper anterior teeth is the first lower anterior tooth row. Like the first and second lower anterior tooth rows, the third lower tooth row is supported by the dental bulla and may be called the first lower intermediate tooth row. The lower intermediate tooth row occludes between the first and second upper lateral tooth rows situated distal to the upper dental bulla, and the rest of the upper and lower tooth rows, all called lateral tooth rows, occlude alternately. Tooth symmetry cannot be used to identify their dental homology. The presence of dental bullae can be regarded as a synapomorphy of Lamniformes and this character is more definable than the "lamnoid tooth pattern." The formation of the tooth pattern appears to be related to the evolution of dental bullae. This study constitutes the first demonstration of supraspecific tooth-to-tooth dental homologies in nonmammalian vertebrates.     

Pharyngeal jaw morphology and homology in Sicydiine Gobies (Teleostei: Gobiidae) and allies

An extremely large number of fifth ceratobranchial teeth, with highly modified, striated, and hooked tips were observed in the central and western Pacific sicydiine goby genus Stiphodon.A scanning electron microscopic study of the form and arrangement of fifth ceratobranchial teeth was conducted to assess the distribution of these modifications in sicydiine gobies and their putative close relatives. Our goals were to explore a new set of characters in gobioid systematics, to test sicydiine monophyly, and to test hypotheses of relationships of sicydiine gobies. Sicydiines are hypothesized herein to be most closely related to the western Pacific Tukugobius and Rhinogobius,freshwater genera with which they share thickened pelvic-fin rays, no teeth on the anterior portion of the fifth ceratobranchial bones, fifth ceratobranchial teeth with differentiated and striated tips, and overlapping anterior rami of the fifth ceratobranchial bones. The latter two characters occur in some, but not all, sicydiines. The pantropical freshwater goby Awaous,often classified with sicydiines, is not considered the closest relative of the subfamily. The highly modified fifth ceratobranchials of Stiphodon are similar to, and concluded here to be homoplasious with, those of the mudflat-dwelling New World goby Evorthodus and the Indo-west Pacific oxudercine gobies, represented in this study by Pseudapocryptes. J. Morphol. 237:257–274, 1998. Published 1998 Wiley-Liss, Inc.     

Morphological analysis of the pharyngeal jaws in two populations of Lebias fasciata Valenciennes, 1821 (Teleostei: Cyprinodontidae)

The study of the pharyngeal jaws in two geographically isolated Italian populations of Lebias fasciata indicated the presence of two phenotypes: the Adriatic phenotype with a large ceratobranchial V and upper and lower pharyngeal jaws bearing few large teeth and the Sicilian phenotype with a smaller ceratobranchial V and pharyngeal jaws with smaller and more numerous teeth. The morphological variations of pharyngeal jaws should be interpreted as a result of the geographical isolation of these two populations. J. Morphol. 241:107–114, 1999. © 1999 Wiley‐Liss, Inc.     

Walking in skates (Chondrichthyes, Rajidae): anatomy, behaviour and analogies to tetrapod locomotion

Pelvic fin walking in skates is common. However, the structure and function of pelvic fins have not been analysed. Pelvic fins of skates of the genus Psammobatis and Rioraja agassizi are externally divided into an anterior leg-like lobe and a posterior fin-like lobe. Internally, the anterior lobes are supported by a compound radial, a proximal radial and distal radials that resemble a thigh, a calf and a foot, respectively, and three associated radials arising from the pelvic girdle. A highly developed radial condyle on the pelvic girdle enables broad 'limb' movements. The muscular arrangement of the anterior lobes is formed by protractor, retractor, flexor and extensor muscles, clearly departing from the generalized fin muscle arrangement of elasmobranchs. Walking is composed of propulsion and recovery phases. A backward movement of the compound radial in the horizontal plane characterizes the propulsive phase. The proximal radial connects vertically the compoundradial with the foot-like distal radials, which are anchored on the bottom. During the recovery phase, the foot-like structure is lifted off the bottom and the entire limb-like anterior lobe is moved forwards for starting a new cycle. Walking in skates resembles the ancestral tetrapod sprawling locomotion seen in many salamanders and lizards. Pelvic fin anatomy and walking behaviour in skates and hemiscylliid sharksare compared. Ecological and evolutionary implications of walking locomotion in skates are also discussed.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 35–41.     

Trophic morphology of the coral-associated genus Gobiodon (Teleostei: Gobiidae) from the Red Sea

Trophic morphology plays a major role in niche diversification among the highly diverse fish fauna of coral reefs. It gives insight into feeding types and is useful in taxonomy, as it can be used to differentiate between species and to estimate phylogenetic relationships. The gobiid genus Gobiodon comprises obligate coral dwelling species that are widespread on Red Sea and Indo-Pacific reefs. Yet very little is known about their ecology and behaviour of feeding. In this study, viscerocranial and oral jaw morphology was investigated in seven species of Gobiodon that occur in the Red Sea. Osteological analyses were carried out on enzyme cleared and alizarin red stained specimens. Shape variation of the viscerocranium was analyzed using a landmark-based geometric morphometric method on digital scans of hand drawings and visualized in thin-plate splines. Shape was determined by placing landmarks on skeletal elements in their articulated state. Morphology of the dentary and premaxilla was examined in further detail after disarticulation. A combination of landmarks and semilandmarks was applied to digital photographs of the oral jaws. It was shown that orbit size influences viscerocranial morphology by delimiting the lower jaw articulation angle. The premaxilla differs both in its extent and direction of curvature and in the structure of the articular process. Form changes in the dentary are mainly caused by variation of curvature and depth. A significant relationship between oral jaw shape and the number of anterior rows of teeth was found. Morphological diversity of selected elements is used to generate hypotheses concerning the trophic biology and niche diversification of Gobiodon . Brief dietary and in situ behavioural observations were carried out to further develop and test hypotheses.     

Scymnodon plunketi (Waite, 1910): a junior synonym of Scymnodon macracanthus (Regan, 1906) (Somniosidae: Elasmobranchii)

The taxonomic status and validity of Scymnodon macracanthus (Regan, 1906) and Scymnodon plunketi (Waite, 1910) are revised in light of new material from the Southern Pacific and Indian Oceans. Despite being historically accepted as distinct taxa, recent studies suggested the possibility that these species could represent a single taxon. Morphometrics, meristics and morphology of dermal denticles show that S. plunketi is indeed a junior synonym of S. macracanthus. Previous distinctive characters proved to be the result of intraspecific variation. S. macracanthus is therefore redescribed including an updated comparative diagnosis for the genus Scymnodon in the family Somniosidae.     

Feeding behavior and kinematics of the lesser electric ray, Narcine brasiliensis (Elasmobranchii: Batoidea)

Jaw protrusion is a major functional motif in fish feeding and can occur during mouth opening or closing. This temporal variation impacts the role that jaw protrusion plays in prey apprehension and processing. The lesser electric ray Narcine brasiliensis is a benthic elasmobranch (Batoidea: Torpediniformes) with an extreme and unique method of prey capture. The feeding kinematics of this species were investigated using high-speed videography and pressure transduction. The ray captures its food by protruding its jaws up to 100% of head length (approximately 20% of disc width) beneath the substrate and generating negative oral pressures (< or = 31 kPa) to suck worms into its mouth. Food is further winnowed from ingested sediment by repeated, often asymmetrical protrusions of the jaws (> 70 degrees deviation from the midline) while sand is expelled from the spiracles, gills and mouth. The pronounced ram contribution of capture (jaw protrusion) brings the mouth close enough to the food to allow suction feeding. Due to the anatomical coupling of the jaws, upper jaw protrusion occurs in the expansive phase (unlike most elasmobranchs and similar to bony fishes), and also exhibits a biphasic (slow-open, fast-open) movement similar to tetrapod feeding. The morphological restrictions that permit this unique protrusion mechanism, including coupled jaws and a narrow gape, may increase suction performance, but also likely strongly constrain dietary breadth.     

Retinal neuropeptides in the skates,Raja clavata,R. radiata,R. oscellata (Elasmobranchii)

Summary The distribution of immunoreactive neuropeptides was investigated in the retina of three species of skates (Raja clavata, R. radiata, R. oscellata), elasmobranch fish often used in electrophysiological work on the retina. Enkephalins, neuropeptide Y (NPY), substance P and glucagon were found in different types of amacrine cells.All four peptides appeared in cell bodies in the innermost part of the inner nuclear layer. Processes from the cells containing enkephalins were numerous and ramified throughout the inner plexiform layer. Processes from the cells containing glucagon were thick and rare, and were found throughout the inner plexiform layer, at times with a predominance in sublaminae 1 and 4. NPY-immunoreactive fibres appeared mainly in sublamina 1 but also in 2 or 3, and substance-P-immunoreactive fibres in sublaminae 1,4 and 5.Antisera against somatostatin, VIP or neurotensin did not show any immunoreactivity in the skate retina.     

Evidence of a counter-current heat exchanger in the ray, Mobula tarapacana (Chondrichthyes: Elasmobranchii: Batoidea: Myliobatiformes)

A vascular network, or rete, has been found in the pectoral fin of the mobulid ray, Mobula tarapacana. This rete appears to be a counter-current heat exchanger which, in conjunction with a high level of red muscle, indicates that this ray is warm-bodied. Preliminary results on other closely related rays indicate that retia may be more common amongst the rays than previously thought.     

中华稻蝗全消化道内壁显微结构观察

本文采用扫描仪和扫描电镜对中华稻蝗消化道内壁的细微结构进行了系统观察和研究。结果表明,中华稻蝗食道内壁由纵行脊组成,前端有齿。嗉囊包括两段,前段的一个小的膨大部分,由V-形区和两侧的V-形脊组成,只在前端内壁有齿;后段为一个大的膨大部分,由柳叶脊、扇形脊和不规则脊组成,脊的上缘有齿。前肠内壁的齿主要为单生齿,除贲门瓣上齿的齿尖指向前方外,全部齿的齿尖指向后方。后肠的前端为12个幽门瓣,内壁有齿。回肠和结肠由6条纵行脊组成,结肠内壁有齿。直肠的齿在除直肠垫外的直肠内壁上。后肠的齿主要为丛生齿,后肠除直肠内壁齿的齿尖指向附着环外,全部齿的齿尖指向后方。根据我们的观察,对前肠提出了新的分区。     

Anatomy and functional morphology of the feeding apparatus of the lesser electric ray, Narcine brasiliensis (Elasmobranchii: Batoidea)

Protrusion of the jaws during feeding is common in Batoidea (rays, skates, sawfishes, and guitarfishes), members of which possess a highly modified jaw suspension. The lesser electric ray, Narcine brasiliensis, preys primarily on polychaete annelids using a peculiar and highly derived mechanism for jaw protraction. The ray captures its prey by protruding its jaws beneath the substrate and generating subambient buccal pressure to suck worms into its mouth. Initiation of this protrusion is similar to that proposed for other batoids, in that the swing of the distal ends of the hyomandibulae is transmitted to Meckel's cartilage. A "scissor-jack" model of jaw protrusion is proposed for Narcine, in which the coupling of the upper and lower jaws, and extremely flexible symphyses, allow medial compression of the entire jaw complex. This results in a shortening of the distance between the right and left sides of the jaw arch and ventral extension of the jaws. Motion of the skeletal elements involved in this extreme jaw protrusion is convergent with that described for the wobbegong shark, Orectolobus maculatus. Narcine also exhibits asymmetrical protrusion of the jaws from the midline during processing, accomplished by unequal depression of the hyomandibulae. Lower jaw versatility is a functional motif in the batoid feeding mechanism. The pronounced jaw kinesis of N. brasiliensis is partly a function of common batoid characteristics: euhyostylic jaw suspension (decoupling the jaws from the hyoid arch) and complex and subdivided cranial musculature, affording fine motor control. However, this mechanism would not be possible without the loss of the basihyal in narcinid electric rays. The highly protrusible jaw of N. brasiliensis is a versatile and maneuverable feeding apparatus well-suited for the animal's benthic feeding lifestyle.     

Constructional morphology within the head of hammerhead sharks (sphyrnidae)

The study of functional trade‐offs is important if a structure, such as the cranium, serves multiple biological roles, and is, therefore, shaped by multiple selective pressures. The sphyrnid cephalofoil presents an excellent model for investigating potential trade‐offs among sensory, neural, and feeding structures. In this study, hammerhead shark species were chosen to represent differences in head form through phylogeny. A combination of surface‐based geometric morphometrics, computed tomography (CT) volumetric analysis, and phylogenetic analyses were utilized to investigate potential trade‐offs within the head. Hammerhead sharks display a diversity of cranial morphologies where the position of the eyes and nares vary among species, with only minor changes in shape, position, and volume of the feeding apparatus through phylogeny. The basal winghead shark, Eusphyra blochii, has small anteriorly positioned eyes. Through phylogeny, the relative size and position of the eyes change, such that derived species have larger, more medially positioned eyes. The lateral position of the external nares is highly variable, showing no phylogenetic trend. Mouth size and position are conserved, remaining relatively unchanged. Volumetric CT analyses reveal no trade‐offs between the feeding apparatus and the remaining cranial structures. The few trade‐offs were isolated to the nasal capsule volume's inverse correlation with braincase, chondrocranial, and total cephalofoil volume. Eye volume also decreased as cephalofoil width increased. These data indicate that despite considerable changes in head shape, much of the head is morphologically conserved through sphyrnid phylogeny, particularly the jaw cartilages and their associated feeding muscles, with shape change and morphological trade‐offs being primarily confined to the lateral wings of the cephalofoil and their associated sensory structures. J. Morphol. 276:526–539, 2015. © 2015 Wiley Periodicals, Inc.     

Further structures in the jaw apparatus of Limnognathia maerski (Micrognathozoa), with notes on the phylogeny of the Gnathifera

The jaws of Limnognathia maerski, Micrognathozoa, were investigated with light- and scanning electron microscopy. The study yielded several new structures and sclerites, including the ventral part of main jaw, the pharyngeal lamellae, the manus, the dorsal and ventral fibularium teeth, and a reinterpretation of the fibularium compartmentalization. Furthermore, it was shown that several jaw elements are composed of densely packed rods. Comparison with Rotifera and Gnathostomulida suggested that the micrognathozoan main jaw is homologous with the rotifer incus and the gnathostomulid articularium and that the pseudophalangids (the ventral jaws) and their associated sclerites correspond to the rotifer mallei. These results imply that Micrognathozoa is more closely related to Rotifera than to Gnathostomulida.     

Functional cranial analysis of large animalivorous bats (Microchiroptera)

Large animalivorous bats include carnivorous, piscivorous and insectivorous microchiropterans. Skull proportions and tooth morphology are examined and interpreted functionally. Four wide- faced bats from four families are convergent in having wide skulls, large masseter muscle volumes and stout jaws, indicating a powerful bite. Three of the four also have long canine teeth relative to their maxillary toothrows. Carnivorous bats have more elongate skulls, larger brain volumes and larger pinnae. The wide-faced bats are all dral emitters and have heads positively tilted relative to the basicranial axis. The carnivorous species are nasal-emitting bats and have negatively tilted heads. The orientation of the head relative to the basicranial axis affects several characters of the skull and jaws and is not correlated with size. The speculation that the type of echolocation may be more of a determinant of evolutionary change than the feeding mechanism is addressed. Wide-faced bats are thought to be capable of eating hard prey items (durophagus) and are probably non- discriminating, aurally less sophisticated insect generalists while the carnivorous and non- durophagus insectivorous bats may be more discriminating and aurally more sophisticated in what they eat.     

Isolation and characterization of eight microsatellite loci from the longheaded eagle ray, Aetobatus flagellum (Elasmobranchii, Myliobatidae)

The longheaded eagle ray, Aetobatus flagellum feeds mainly on bivalves, and there have been some indications that the current reduction in the bivalve population in southern Japan may be due to an increase in the number of longheaded eagle rays. Consequently, the 'predator control programme' for reducing the longheaded eagle ray population was established in 2001 in Japan. For studying the population genetics of the longheaded eagle ray, we isolated eight polymorphic microsatellite loci (two to six alleles per locus; expected heterozygosity, 0.172-0.700) from this species.