Inter‐ and intraspecific variation in the distribution and number of pit organs (free neuromasts) of sharks and rays

Abstract

The distribution of pit organs (free neuromasts) has previously been documented for several species of pelagic sharks, but is relatively poorly known for rays and bottom-dwelling (demersal) sharks. In the present study, the complete distribution of pit organs was mapped in the demersal sharks Heterodontus portusjacksoni, Orectolobus maculatus, Hemiscyllium ocellatum, Chiloscyllium punctatum, and Asymbolus analis, and the rays Rhinobatos typus, Aptychotrema rostrata, Trygonorrhina sp. A, Raja sp. A, and Myliobatis australis. All of these species had pit organs scattered over the dorsolateral surface. The sharks also had "mandibular" pit organs (and "umbilical" pit organs in C. punctatum and A. analis) on the ventral surface, while pit organs were sparse or absent on the ventral surface of rays. All of the species examined here, except for M. australis, also had a "spiracular" group of pit organs adjacent to the eye and/or spiracle. Spiracular pit organs were also recorded for the sawshark Pristiophorus sp. A and the skate Pavoraja nitida, although the remainder of pit organs were not mapped in these species. The distribution and number of pit organs varied both within and among species. Pit organ distribution was asymmetrical in each individual examined, but no particular trend towards left or right "handedness" was observed in any species. Although rays have been thought to have fewer pit organs than sharks in general, this was not the case in the present study. All of the species examined here had few pit organs compared to the pelagic sharks previously documented, but it is not clear whether this is due to ecological or phylogenetic causes.

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

“…In rays, pit organs are associated with grooves in the skin surface, whereas the pit organs of sharks are found between modified denticles (Maruska 2001;Peach 2003). Pit organs encode water velocity and in Heterodontus portusjacksoni they are used to orientate the body in water currents (Peach 2001).…”

“…Pit organs encode water velocity and in Heterodontus portusjacksoni they are used to orientate the body in water currents (Peach 2001). Pit organs are distributed asymmetrically across the body, and to date, there has been no indication of any left or right-handedness in pit organ counts (Peach 2003).…”

Contribution to the Taxonomy and Distribution of Six Shark Species (Chondrichthyes, Elasmobranchii) from the Gulf of Thailand

“…In the future the pit organs might possibly be used in support of the determination of sharks, because the abundance and distribution of these free neuromasts vary widely among species according to Budker [48], Tester and Nelson [49] and Peach [50]. However, further research including the examination of more species is needed to verify if there are species-specific patterns of pit organs and, if so, to characterize the different typal patterns.…”

Morphology of lateral line canals in Neotropical freshwater stingrays (Chondrichthyes: Potamotrygonidae) from Negro River, Brazilian Amazon

“…Peach & Marshall (2000) and Peach (2003) demonstrated the importance of free neuromasts for prey detection under low light conditions as well as their chemoreceptor functions (Katsuki et al, 1969). Free neuromasts were not examined in the present study, and a more complete knowledge of their function may provide valuable additional information about the biology and behavior of potamotrygonid species in the typically low visibility environments of rivers in the Amazon basin.…”

“…The lateral line system occurs in all aquatic amphibians and fishes, and represents an important detector of water movements near the skin surface (Maruska & Tricas, 1998;Bleckmann & Hofmann, 1999;Peach & Marshall, 2000;Maruska, 2001;Peach, 2003). Different types of lateral line organs are found in chondrichthyans, although their functions are still not well understood (Barry & Bennett, 1989;Maruska, 2001).…”