Comparison of the lateral line and ampullary systems of two species of shovelnose ray

The anatomical characteristics of the mechanoreceptive lateral line system and electrosensory ampullae of Lorenzini of Rhinobatos typus and Aptychotrema rostrata are compared. The spatial distribution of somatic pores of both sensory systems is quite similar, as lateral line canals are bordered by electrosensory pore fields. Lateral line canals form a sub-epidermal, bilaterally symmetrical net on the dorsal and ventral surfaces; canals contain a nearly continuous row of sensory neuromasts along their length and are either non-pored or pored. Pored canals are connected to the surface through a single terminal pore or additionally possess numerous tubules along their length. On the dorsal surface of R. typus, all canals of the lateral line occur in the same locations as those of A. rostrata. Tubules branching off the lateral line canals of R. typus are ramified, which contrasts with the straight tubules of A. rostrata. The ventral prenasal lateral line canals of R. typus are pored and possess branched tubules in contrast to the non-pored straight canals in A. rostrata. Pores of the ampullae of Lorenzini are restricted to the cephalic region of the disk, extending only slightly onto the pectoral fins in both species. Ampullary canals penetrate subdermally and are detached from the dermis. Ampullae occur clustered together, and can be surrounded by capsules of connective tissue. We divided the somatic pores of the ampullae of Lorenzini of R. typus into 12 pore fields (10 in A. rostrata), corresponding to innervation and cluster formation. The total number of ampullary pores found on the ventral skin surface of R. typus is approximately six times higher (four times higher in A. rostrata) than dorsally. Pores are concentrated around the mouth, in the abdominal area between the gills and along the rostral cartilage. The ampullae of both species of shovelnose ray are multi-alveolate macroampullae, sensu Andres and von Düring (1988). Both the pore patterns and the distribution of the ampullary clusters in R. typus differ from A. rostrata, although a basic pore distribution pattern is conserved.     

Comparative morphology of the electrosensory system of the epaulette shark Hemiscyllium ocellatum and brown-banded bamboo shark Chiloscyllium punctatum

We compared the electrosensory system of two benthic elasmobranchs Hemiscyllium ocellatum and Chiloscyllium punctatum. The distribution of the ampullary pores on the head was similar for both species, with a higher density of pores anteriorly and a lower density posteriorly, although C. punctatum generally possessed larger pores. Ampullary canals of the mandibular cluster were quasi-sinusoidal in H. ocellatum, a shape previously found in benthic rays only, whereas ampullary canals in C. punctatum were of a linear morphology as reported for many shark and ray species previously. The ampullae proper were of the lobular type, as occurs in most galean sharks. Chiloscyllium punctatum had six sensory chambers compared with the five per ampulla in H. ocellatum, which were generally smaller than those of C. punctatum. The sensory epithelium comprised flattened receptor cells, compared with the usual pear-shaped receptor cells encountered in other elasmobranchs and their apically nucleated supportive cells did not protrude markedly into the ampullary lumen, unlike those in benthic rays.     

The Neuroecology of the Elasmobranch Electrosensory World: Why Peripheral Morphology Shapes Behavior

The adaptations of elasmobranch sensory systems can be studied by linking the morphological structure with the natural behavior and ecology of the organism. This paper presents the first step in a neuroecological approach to interpret the spatial arrangement of the electrosensory ampullary organs in elasmobranch fishes. A brief review of the structure and function of the ampullae of Lorenzini is provided for interpretation of the organ system morphology in relation to the detection of dipole and uniform electric fields. The spatial projections of canals from discrete ampullary clusters were determined for the barndoor skate, Raja laevis, based upon a published figure in Raschi (1986), and measured directly from the head of the white shark, Carcharodon carcharias. The dorsoventrally flattened body of the skate restricts the projections of long canals to the horizontal plane. There is a distinct difference between dorsal and ventral projection patterns in all groups. Notable within-cluster features include a relatively long canal subgroup in the dorsal superficial ophthalmic (SOd) and dorsal hyoid (HYOd) clusters that are oriented parallel (bidirectionally) to the longitudinal axis of the body. It is postulated that this subgroup of canals may be important for detection and orientation to weak uniform fields. Ventral canal projections in the skate are primarily lateral, with the exception of the hyoid (HYOv) that also projects medially. This wide dispersion may function for the detection of prey located below the body and pectoral fins of the skate, and may also be used for orientation behavior. The mandibular canals located near the margin of the lower jaw (of both study species) are ideally positioned for use during prey manipulation or capture, and possibly for interspecific courtship or biting. The head of the white shark, which lacks the hyoid clusters, is ovoid in cross section and thus ampullary canals can project into three-dimensional space. The SOd and superficial ophthalmic ventral (SOv) clusters show strong rostral, dorsal and lateral projection components, whereas the SOv also detects rostral fields under the snout. In the sagittal plane, the SOv and SOd have robust dorsal projections as well as ventral in the SOv. Most notable are canal projections in the white shark buccal (BUC) ampullary cluster, which has a radial turnstile configuration on the ventrolateral side of the snout. The turnstile design and tilt between orthogonal planes indicates the white shark BUC may function in detection of uniform fields, including magnetically induced electric fields that may be used in orientation behaviors. These data can be used in future neuroecology behavioral performance experiments to (1) test for possible specializations of cluster groups to different natural electric stimuli, (2) the possibility of specialized canal subgroups within a cluster, and (3) test several models of navigation that argue for the use of geomagnetically induced electric cues.     

Morphology of the ampullae of Lorenzini in juvenile freshwater Carcharhinus leucas

Ampullae of Lorenzini were examined from juvenile Carcharhinus leucas (831–1,045 mm total length) captured from freshwater regions of the Brisbane River. The ampullary organ structure differs from all other previously described ampullae in the canal wall structure, the general shape of the ampullary canal, and the apically nucleated supportive cells. Ampullary pores of 140–205 µm in diameter are distributed over the surface of the head region with 2,681 and 2,913 pores present in two sharks that were studied in detail. The primary variation of the ampullary organs appears in the canal epithelial cells which occur as either flattened squamous epithelial cells or a second form of pseudostratified contour‐ridged epithelial cells; both cell types appear to release material into the ampullary lumen. Secondarily, this ampullary canal varies due to involuted walls that form a clover‐like canal wall structure. At the proximal end of the canal, contour‐ridged cells abut a narrow region of cuboidal epithelial cells that verge on the constant, six alveolar sacs of the ampulla. The alveolar sacs contain numerous receptor and supportive cells bound by tight junctions and desmosomes. Pear‐shaped receptor cells that possess a single apical kinocilium are connected basally by unmyelinated neural boutons. Opposed to previously described ampullae of Lorenzini, the supportive cells have an apical nucleus, possess a low number of microvilli, and form a unique, jagged alveolar wall. A centrally positioned centrum cap of cuboidal epithelial cells overlies a primary afferent lateral line nerve. J. Morphol. 276:481–493, 2015. © 2014 Wiley Periodicals, Inc.     

A comparison of the electrosensory morphology of a euryhaline and a marine stingray

The electrosensory system is found in all chondrichthyan fishes and is used for several biological functions, most notably prey detection. Variation in the physical parameters of a habitat type, i.e. water conductivity, may influence the morphology of the electrosensory system. Thus, the electrosensory systems of freshwater rays are considerably different from those of fully marine species; however, little research has so far examined the morphology and distribution of these systems in euryhaline elasmobranchs. The present study investigates and compares the morphology and distribution of electrosensory organs in two sympatric stingray species: the (euryhaline) estuary stingray, Dasyatis fluviorum, and the (marine) blue-spotted maskray, Neotrygon kuhlii. Both species possess a significantly higher number of ventral electrosensory pores than previously assessed elasmobranchs. This correlates with a diet consisting of benthic infaunal and epifaunal prey, where the electrosensory pore distribution patterns are likely to be a function of both ecology and phylogeny. The gross morphology of the electrosensory system in D. fluviorum is more similar to that of other marine elasmobranch species, rather than that of freshwater species. Both D. fluviorum and N. kuhlii possess ‘macro-ampullae’ with branching canals leading to several alveoli. The size of the pores and the length of the canals in D. fluviorum are smaller than in N. kuhlii, which is likely to be an adaptation to habitats with lower conductivity. This study indicates that the morphology of the electrosensory system in a euryhaline elasmobranch species seems very similar to that of their fully marine counterparts. However, some morphological differences are present between these two sympatric species, which are thought to be linked to their habitat type.     

A morphological analysis of the ampullae of Lorenzini in selected skates (Pisces,Rajoidei)

A comparison of the ampullae of Lorenzini among 40 species of skates (Rajoidei) demonstrates a close relationship between inferred electroreceptive capabilities and feeding mechanisms. Three general lines of morphological modifications are noted. (1) Whereas the majority of ampullary pores are located on the ventral surface of the dorsoventrally flattened body, the relative proportion of ventral pores is significantly lower on species inhabiting aphotic waters. (2) The ventral pores on more piscivorous species are distributed over a larger portion of body surface than they are on those species that feed primarily on invertebrates. Ventral pores in this latter group are more noticeably concentrated around the mouth and their densities on the adult are inversely related to the overall mobility of preferred prey species. (3) The size of each ampulla and the number of alveoli associated with it are directly related to the habitat depth occupied by each species. Shallow-water species have smaller ampullae with fewer alveoli than deeper-dwelling (> 1,000 m) species. The general distribution of ampullary pores on deep dwelling rajoids appears to compensate for reduced visual input, whereas their relative densities are a measure of the system's resolution and reflect major differences in feeding strategies. The increased ampullary size and complexity observed in deep-sea rajoids provides mechanisms to increase both the sensitivity and signal-to-noise ratios.     

A study into the sexual dimorphisms of the Ampullae of Lorenzini in the lesser-spotted catshark, Scyliorhinus canicula (Linnaeus, 1758)

The Ampullae of Lorenzini can vary in their size, shape and distribution patterns among elasmobranch species. However, no study has compared the ampullary characteristics between the sexes within a species. The present study found a sexual dimorphism in the Ampullae of Lorenzini of the lesser-spotted catshark, Scyliorhinus canicula. Male S. canicula were found to possess longer ampullae and alveoli, greater numbers of alveolar bulbs, larger sensory epithelial surface areas and greater numbers of sensory receptor cells in the ampullae than female S. canicula. Greater lengths of both ampullae and alveoli, numbers of alveoli, larger sensory epithelial surface areas and greater numbers of sensory receptor cells in male S. canicula could increase the capability of adult male S. canicula in detecting females. The presence of the sexual dimorphism in the alveoli of the Ampullae of Lorenzini could be directly related to reproductive behaviour and/or reflect the sexual segregation patterns of adult S. canicula.     

Ampullary organs and electroreception in freshwater Carcharhinus leucas.

The ampulla of Lorenzini of juvenile Carcharhlinus leucas differ histologically from those previously described for other elasmobranchs. The wall of the ampullary canal consists of protruding hillock-shaped epidermal cells that appear to secrete large quantities of a mucopolysaccharide gel. The ampullary organs comprise a long canal sheathed in collagen terminating in an ampulla. Each ampulla contains six alveolar sacs, with each sac containing hundreds of receptor cells. The receptor cells are characteristic of others described for elasmobranchs being pear-shaped cells with a central nucleus and bearing a single kinocilium in the exposed apical region of the cell. The supportive cells differ from general elasmobranch ampullary histology in that some have an apical nucleus. These ampullary structures allow Carcharhinus leucas to detect and respond to artificial electrical fields. Carcharhinus leucas from freshwater habitats respond to electrical signals supplied in freshwater aquaria by abruptly turning towards low voltage stimuli (< or = 10 microA) and either swimming over or biting at the origin of the stimulus.     

Ultrastructure of the ampullae of Lorenzini of <Emphasis Type="Italic">Aptychotrema rostrata</Emphasis> (Rhinobatidae)

Small epidermal pores of the electrosensory ampullae of Lorenzini located both ventrally and dorsally on the disk of Aptychotrema rostrata (Shaw and Nodder, 1794) open to jelly-filled canals, the distal end of which widens forming an ampulla that contains 6 ± 0.7 alveolar bulbs (n = 13). The sensory epithelium is restricted to the alveolar bulbs and consists of receptor cells and supportive cells. The receptor cells are ellipsoid and their apical surfaces are exposed to the alveolar lumen with each bearing a single central kinocilium. Presynaptic bodies occur in the basal region of the receptor cell immediately proximal to the synaptic terminals. The supportive cells that surround receptor cells vary in shape. Microvilli originate from their apical surface and extend into the alveolar lumen. Tight junctions and desmosomes connect the supportive cells with adjacent supportive and receptor cells in the apical region. The canal wall consists of two cell layers, of which the luminal cells are squamous and interconnect via desmosomes and tight junctions, whereas the cells of the deeper layer are heavily interdigitated, presumably mechanically strengthening the canal wall. Columnar epithelial cells form folds that separate adjacent alveoli. The same cells separate the ampulla and canal wall. An afferent sensory nerve composed of up to nine myelinated nerve axons is surrounded by several layers of collagen fibers and extends from the ampulla. Each single afferent neuron can make contacts with multiple receptor cells. The ultrastructural characteristics of the ampullae of Lorenzini in Aptychotrema rostrata are very similar to those of other elasmobranch species that use electroreception for foraging.     

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.     

Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs

Electroreception is found throughout the animal kingdom from invertebrates to mammals and has been shown to play an important role in prey detection, facilitating social behaviours, the detection of predators and orientation to the earth's magnetic field for navigation. Electroreceptors in elasmobranchs, the ampullae of Lorenzini, detect minute electric fields and independently process these stimuli, thereby providing spatial information to the central nervous system on the location of a source, often potential prey. The ampullae of Lorenzini are individually connected to a single somatic pore on the surface of the skin, with the spatial separation of each pore directly influencing how electrical stimuli are detected and processed. Pore abundance varies across taxonomic groups resulting in unique species-specific differences. The intricate distribution patterns created by the specific positioning of somatic pores on the head are, however, consistent within families, resulting in patterns that are identifiable at higher taxonomic levels. As elasmobranchs evolved, the electrosensory system became more complex and highly specialized, which is evident by a general trend of increasing pore abundance over time. The elasmobranch electrosensory system has evolved to operate efficiently under the environmental conditions of the particular habitat in which a species lives. For example, reduced pore abundance is evident in oceanic pelagic elasmobranchs, for whom visual cues are thought to be of great importance. Pore abundance and spatial distribution may be influenced by multiple factors including head morphology, phylogeny, feeding behaviour and habitat.     

The Morphology of the Lorenzinian Ampullae of the Sturgeon Acipenser ruthenus (Pisces: Chondrostei)

Jørgensen, J. M. 1980. The morphology of the Lorenzinian ampullae of the sturgeon Acipenser ruthenus (Pisces: Chondrostei). (Zoological Laboratory, University of Aarhus, Denmark.) — Acta zool. (Stockh.) 61 (2): 87–92. The snout of a sturgeon, Acipenser ruthenus (Chondrostei, Osteichthyes) is provided with sensory pores. Light and electron microscopical examination of these reveals that the ampullary organs have a sensory epithelium very similar to what has been found in the Lorenzinian ampullae, which are electroreceptors previously examined at a fine structural level in elasmobranchs and the paddle-fish, Polyodon spathula. The sensory cells are pear-shaped with a very small apical part, in the centre of which there is a short cilium. Basally, the sensory cells make several contacts with button-shaped nerve-endings. The presumed synaptic area in the sensory cell is characterized by a presynaptic sheet surrounded by vesicles. Only one type of nerve ending, an afferent type, has been observed.     

Morphology of the teleost ampullary organs in marine salmontail catfish Neoarius graeffei (Pisces: Ariidae) with comparative analysis to freshwater and estuarine conspecifics

We hypothesized that due to the relative conductivity of the environment, and to maintain sensory function, ampullary organs of marine Neoarius graeffei would differ morphologically from those described previously for estuarine and freshwater conspecifics. Unlike the ampullary systems of N. graeffei from freshwater and estuarine habitats, the ampullary pores of marine specimens occur in two distinct patterns; numerous pores seemingly randomly scattered on the head and ventro‐lateral regions of the body, and pores arranged in distinctive vertical lines above the lateral line on the dorso‐lateral body of the fish. Light and electron microscopy revealed that the ampullary organs also differed morphologically from estuarine and freshwater specimens in the presence of longer ampullary canals, a hitherto unreported canal wall composition, and in the collagen sheath surrounding both the canal and the ampulla proper within dermal connective tissues. Ampullary pores were wider in marine individuals and opened to the longest ampullary canals reported for this species. The canal wall was lined by cuboidal and squamous epithelial cells. Each ampullary canal opened into a single ampulla proper containing significantly more receptor cells than estuarine and freshwater conspecifics. The distribution of ampullary pores as well as the microstructure of the ampullary organs indicates that the electrosensory system of marine N. graeffei differs from those of estuarine and freshwater specimens in ways that would be expected to maintain the functionality of the system in a highly conductive, fully marine environment, and reveals the remarkable plasticity of this species’ ampullary system in response to habitat conductivity. J. Morphol. 276:1047–1054, 2015. © 2015 Wiley Periodicals, Inc.     

Distribution and morphology of the ampullary organs of the salmontail catfish,Arius graeffei

Whole body staining of Arius graeffei revealed that ampullary pores cover the body with their highest densities occurring on the head and lowest densities on the mid‐ventral surface. Each ampullary organ consists of a long canal (0.2–1.75 mm) passing perpendicular to the basement membrane, through the epidermis into underlying dermal connective tissues, curving thereafter to run roughly parallel to the epidermis. Histochemical staining techniques (Alcian blue and Lillie′s allochrome) indicate that the canals contain a neutral to acidic glycoprotein‐based mucopolysaccharide gel that varies in composition along the length of the canal. Collagen fibers, arranged in a sheath, surround a layer of squamous epithelium that lines each ampullary canal. At the proximal end of the canal, squamous cells are replaced by cuboidal epithelial cells that protrude into the lumen, thus constricting the lumen to form a small pore into the ampulla. The ampulla is lined with receptor and supportive cells. The numerous (60–120) pear‐shaped receptor cells bear microvilli on their luminal surface. Two forms of receptor cells exist in each ampullary organ: basal and equatorial receptor cells. Each receptor cell is connected to an unmyelinated nerve. Each receptor cell is surrounded by supportive cells on all but the apex. Tight junctions and underlying desmosomes occur between adjacent receptor and supportive cells. This form of ampullary organ has not previously been described for teleosts. J. Morphol. 239:97–105, 1999. © 1999 Wiley‐Liss, Inc.     

Special cutaneous receptor organs of fish. IV. Ampullary organs of the nonelectric catfish, Kryptopterus

Ampullary organs of the transparent catfish, Kryptopterus bicirrhus, are present in large numbers on the head and in a regular pattern of lines on the body and fins. The organs lie in the epidermis, and have a pore that opens to the surface. Flattened cells form a roof and walls. On the floor of the organ there are a “sensory hillock,” composed of spherical receptor cells and columnar supporting cells, and a “secretory hillock” composed of columnar secretory cells. The receptor cells are nonciliated and have only afferent innervation. The organ cavity is filled with jelly. The organs are compared with ampullary organs of the weakly electric fish Eigenmannia, ampullae of Lorenzini of Raja, and small pit organs of Amiurus. Structural characteristics of the ampullary organs of Kryptopterus make them especially suitable for electrophysiological studies.     

Electrosensitive spatial vectors in elasmobranch fishes: implications for source localization

The electrosense of sharks and rays is used to detect weak dipole-like bioelectric fields of prey, mates and predators, and several models propose a use for the detection of streaming ocean currents and swimming-induced fields for geomagnetic orientation. We assessed pore distributions, canal vectors, complementarity and possible evolutionary divergent functions for ampullary clusters in two sharks, the scalloped hammerhead (Sphyrna lewini) and the sandbar shark (Carcharhinus plumbeus), and the brown stingray (Dasyatis lata). Canal projections were determined from measured coordinates of each electrosensory pore and corresponding ampulla relative to the body axis. These species share three ampullary groups: the buccal (BUC), mandibular (MAN) and superficial ophthalmic (SO), which is subdivided into anterior (SOa) and posterior (SOp) in sharks. The stingray also has a hyoid (HYO) cluster. The SOp in both sharks contains the longest (most sensitive) canals with main projections in the posterior-lateral quadrants of the horizontal plane. In contrast, stingray SO canals are few and short with the posterior-lateral projections subsumed by the HYO. There was strong projection coincidence by BUC and SOp canals in the posterior lateral quadrant of the hammerhead shark, and laterally among the stingray BUC and HYO. The shark SOa and stingray SO and BUC contain short canals located anterior to the mouth for detection of prey at close distance. The MAN canals of all species project in anterior or posterior directions behind the mouth and likely coordinate prey capture. Vertical elevation was greatest in the BUC of the sandbar shark, restricted by the hammerhead cephalofoil and extremely limited in the dorsoventrally flattened stingray. These results are consistent with the functional subunit hypothesis that predicts specialized ampullary functions for processing of weak dipole and geomagnetic induced fields, and provides an anatomical basis for future experiments on central processing of different forms of relevant electric stimuli.     

Morphology of the Mechanosensory Lateral Line System in Elasmobranch Fishes: Ecological and Behavioral Considerations

The relationship between morphology of the mechanosensory lateral line system and behavior is essentially unknown in elasmobranch fishes. Gross anatomy and spatial distribution of different peripheral lateral line components were examined in several batoids (Raja eglanteria, Narcine brasiliensis, Gymnura micrura, and Dasyatis sabina) and a bonnethead shark, Sphyrna tiburo, and are interpreted to infer possible behavioral functions for superficial neuromasts, canals, and vesicles of Savi in these species. Narcine brasiliensis has canals on the dorsal surface with 1 pore per tubule branch, lacks a ventral canal system, and has 8–10 vesicles of Savi in bilateral rows on the dorsal rostrum and numerous vesicles ( = 65 ± 6 SD per side) on the ventral rostrum. Raja eglanteria has superficial neuromasts in bilateral rows along the dorsal body midline and tail, a pair anterior to each endolymphatic pore, and a row of 5–6 between the infraorbital canal and eye. Raja eglanteria also has dorsal canals with 1 pore per tubule branch, pored and non-pored canals on the ventral surface, and lacks a ventral subpleural loop. Gymnura micrura has a pored dorsal canal system with extensive branch patterns, a pored ventral hyomandibular canal, and non-pored canal sections around the mouth. Dasyatis sabina has more canal pores on the dorsal body surface, but more canal neuromasts and greater diameter canals on the ventral surface. Sphyrna tiburo has primarily pored canals on both the dorsal and ventral surfaces of the head, as well as the posterior lateral line canal along the lateral body surface. Based upon these morphological data, pored canals on the dorsal body and tail of elasmobranchs are best positioned to detect water movements across the body surface generated by currents, predators, conspecifics, or distortions in the animal's flow field while swimming. In addition, pored canals on the ventral surface likely also detect water movements generated by prey. Superficial neuromasts are protected from stimulation caused by forward swimming motion by their position at the base of papillar grooves, and may detect water flow produced by currents, prey, predators, or conspecifics. Ventral non-pored canals and vesicles of Savi, which are found in benthic batoids, likely function as tactile or vibration receptors that encode displacements of the skin surface caused by prey, the substrate, or conspecifics. This mechanotactile mechanism is supported by the presence of compliant canal walls, neuromasts that are enclosed in wide diameter canals, and the presence of hair cells in neuromasts that are polarized both parallel to and nearly perpendicular to the canal axis in D. sabina. The mechanotactile, schooling, and mechanosensory parallel processing hypotheses are proposed as future directions to address the relationships between morphology and physiology of the mechanosensory lateral line system and behavior in elasmobranch fishes.     

<Emphasis Type="Italic">Dipturus wuhanlingi</Emphasis>, a new species of skates (Elasmobranchii: Rajidae) from China

Dipturus wuhanlingi, a new rajid species, is described from an immature male and female collected from the southern East China Sea and off Haimen, Shantou, in the South China Sea, respectively. The specimens conform to the genus Dipturus in having the combination of the following characters: a long rostral cartilage (length more than 60% of dorsal head length), greatly depressed and laterally expanded mesocondyle, and a total length greater than 55 cm when adult. Dipturus wuhanlingi is distinct from all other Dipturus species in the following combination of characters: a pair of scapular thorns, three or four nuchal thorns, an irregular row of lumbar thorns along the dorsal midline of the disc, a single row of tail thorns in both sexes, pores of ampullae of Lorenzini extending to just anterior to the pelvic girdle, anterior fenestra of scapulocoracoid strongly horizontally elliptical, mesocondyle located at about the middle between the procondyle and metacondyle, and three pairs of obturator foramina on the pelvic girdle.     

Monocotylids (Monogenoidea) infecting elasmobranchs in Moreton Bay,Queensland, Australia,with descriptions of Calicotyle cutmorei n. sp. (Calicotylinae) and Dendromonocotyle raiae n. sp. (Monocotylinae)

Eighteen monocotylid species were collected from elasmobranchs during surveys of the parasites of fishes of Moreton Bay, Queensland, Australia. Two new species, Calicotyle cutmorei n. sp. (Calicotylinae) from Carcharhinus sorrah (Valenciennes) (Carcharhiniformes) and Dendromonocotyle raiae n. sp. (Monocotylinae) from Hemitrygon fluviorum (Ogilby) and Neotrygon trigonoides (Castelnau) (both Myliobatiformes) are described and illustrated. Six new faunal records for Moreton Bay are reported: Thaumatocotyle australensis Beverley-Burton & Williams, 1989 (Merizocotylinae) from Maculabatis toshi (Whitley) (Myliobatiformes); Monocotyle corali Chisholm, 1998 (Monocotylinae) from Pastinachus ater (Macleay) (Myliobatiformes); Neoheterocotyle rhynchobatis (Tripathi, 1959) Chisholm, 1994 (Heterocotylinae) from Glaucostegus typus (Anonymous [Bennett]) and Aptychotrema rostrata (Shaw) (both Rhinopristiformes); and Decacotyle elpora Marie & Justine, 2005 (Decacotylinae), Dendromonocotyle torosa Chisholm & Whittington, 2004 (Monocotylinae), and Clemacotyle australis Young, 1967 (Monocotylinae) from Aetobatus ocellatus (Kuhl) (Myliobatiformes). Maculabatis toshi is a new host record for T. australensis, and A. rostrata is a new host record for N. rhynchobatis. Ten species previously recorded from Moreton Bay were collected: Monocotyle caseyae Chisholm & Whittington, 2005 (Monocotylinae) and Heterocotyle whittingtoni Chisholm & Kritsky, 2020 (Heterocotylinae) from M. toshi; Monocotyle sp. A of Chisholm (1998a) (Monocotylinae) from H. fluviorum; Dendromonocotyle kuhlii Young, 1967 and Monocotyle kuhlii Young, 1967 (both Monocotylinae) from N. trigonoides; Thaumatocotyle cf. pseudodasybatis Hargis, 1955 (Merizocotylinae), Empruthotrema kearni Whittington, 1990 (Merizocotylinae) and Decacotyle octona Young, 1967 (Decacotylinae) from A. ocellatus; and Mycteronastes icopae (Beverley-Burton & Williams, 1989) Kearn & Beverley-Burton, 1990 (Merizocotylinae) and Troglocephalus rhinobatidis Young, 1967 (Dasybatotreminae) from G. typus.

     

Head Morphology and Electrosensory Pore Distribution of Carcharhinid and Sphyrnid Sharks

Selection to maximize electroreceptive search area might have driven evolution of the cephalofoil head morphology of hammerhead sharks (family Sphyrnidae). The enhanced electrosensory hypothesis predicts that the wider head of sphyrnid sharks necessitates a greater number of electrosensory pores to maintain a comparable pore density. Although gross head morphology clearly differs between sphyrnid sharks and their closest relatives the carcharhinids, a quantitative examination is lacking. Head morphology and the distribution of electrosensory pores were compared between a carcharhinid, Carcharhinus plumbeus, and two sphyrnid sharks, Sphyrna lewini and S. tiburo. Both sphyrnids had greater head widths than the carcharhinid, although head surface area and volume did not differ between the three species. The raked head morphology of neonatal S. lewini pups, presumably an adaptation to facilitate parturition, becomes orthogonal to the body axis immediately post-parturition whereas this change is much less dramatic for the other two species. The general pattern of electrosensory pore distribution on the head is conserved across species despite the differences in gross head morphology. Sphyrna lewini has a mean of 3067 ± 158.9 SD pores, S. tiburo has a mean of 2028 ± 96.6 SD pores and C. plumbeus has a mean of 2317 ± 126.3 SD pores and the number of pores remains constant with age. Sphyrnids have a greater number of pores on the ventral surface of the head whereas C. plumbeus has an even distribution on dorsal and ventral surfaces. The greater number of pores distributed on a similar surface area provides S. lewini pups with a higher density of electrosensory pores per unit area compared to C. plumbeus pups. The greater number of ampullae, the higher pore density and the larger sampling area of the head combine to provide hammerhead sharks with a morphologically enhanced electroreceptive capability compared to comparably sized carcharhinids.