The dermatomes of the pectoral and pelvic fin of the long-tail stingray Himantura fai

Recorded action potentials in whole spinal nerves during mechanical stimulation of the skin of Himantura fai revealed that sequential nerves innervated sequential overlapping strips of the pectoral and pelvic fin skin. As found in previous studies, in which the dermatomes of the skate Raja clavata were measured behaviourally, approximately one-third of the rostral and caudal regions of each dermatome overlapped with the adjacent dermatomes. Consistent with dermatomal maps from non-mammalian vertebrates, but unlike the dermatomal maps obtained in mammals, there appears to be little difference in dermatome size when measured behaviourally or electrophysiologically. We suggest that neural mechanisms of the spinal cord, which appear to contribute to the discrepancy between behaviourally and electrophysiologically mapped dermatomes in mammals, are of negligible influence in stingrays.