The morphology of the pit organs and lateral line canal neuromasts of Mustelus antarcticus (Chondrichthyes : Triakidae)

The pit organs (free neuromasts) of sharks are part of the lateral line sen sory system, but there is still confusion about their exact morphology and function(s). This is partly because of reported physiological differences b etween the pit organs and the lateral line canal neuromasts, and partly bec ause the morphology of pit organs has not been adequately documented. To co mpare their morphology, the pit organs and canal neuromasts of the gummy sh ark Mustelus antarcticus (Chondrichthyes: Triakidae) were examined using tr ansmission and scanning electron microscopy. Both pit organs and canal neur omasts had hair cells with the 'staircase' arrangement of sensory hairs (st ereovilli) characteristic of vertebrate mechanoreceptors. Stereovilli bundl es of different sizes were distributed haphazardly throughout the pit organ s and canal neuromasts. The density of hair cells was similar in the pit or gans and canal neuromasts, but differences in the overall size and/or shape of the sensory epithelia might account for some of the reported difference s in mechanosensitivity.