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

Abstract

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.

Description of the mechanoreceptive lateral line and electroreceptive ampullary systems in the freshwater whipray, Himantura dalyensis

“…This provides further evidence for the importance of close-range senses for a benthic diet, which predominantly consists of benthic crustaceans and benthic teleost fishes (Last and Stevens 2009). Similar to the findings of Raschi (1986) on Raja species, the highest density of ampullary pores in H. dalyensis is located around the mouth, providing the necessary resolution to direct a strike after prey localisation (Raschi 1986 (Jordan 2008;Wueringer and Tibbetts 2008). The difference in total ventral pore counts between H. dalyensis and P. violacea may reflect their dissimilar ecological niches.…”

“…The complex organisation of the highly ramified tubules may increase the sampling area on the skin, thereby increasing its sensitivity to hydrodynamic flow across this plane (Wueringer and Tibbetts 2008). This may enhance the abilities of H. dalyensis to detect prey and conspecifics and also to navigate in turbid river systems.…”

“…Methylene blue (0.3%) was utilised as a stain following the method of Wueringer and Tibbetts (2008). Specimens were viewed under a Wild Heerbrugg M650 dissecting microscope (Heerbrugg, Switzerland).…”

“…Despite these unique senses being extensively studied over recent years (i.e. Maruska and Tricas 1998;Kajiura 2003;Wueringer and Tibbetts 2008), there is still a paucity of research focussing on these senses in freshwater elasmobranchs. In addition, there is a severe lack of information on the recently described Himantura dalyensis, supposedly one of Australia's few oligohaline elasmobranchs (Thorburn et al 2004;.…”

“…Ampullae of Lorenzini are located subcutaneously and are linked to the external environment via a canal that connects to a somatic pore. Ampullae are clustered and are often surrounded by capsules of connective tissue, thereby eliminating interference produced by the animal's own electric field (Murray 1974;Wueringer and Tibbetts 2008). Three types of ampullary systems were described by Andres and von Düring (1988): (1) macro-ampullae, which possess elongated canals that terminate in ampullary bulbs, are the most common type of ampullae of Lorenzini, common in marine elasmobranchs, and can be clustered together; (2) micro-ampullae, which are highly reduced ampullae of Lorenzini (Raschi et al 1997), found primarily in hexanchid sharks and holocephali; and (3) mini-ampullae, which are microscopic ampullae of Lorenzini of freshwater rays in the genus Potamotrygon (Szabo et al 1972), are not located in clusters, most likely due to their minute size.…”