Among European colubroids, scale sensilla—mechanoreceptors present in the head integument—are more expressed in natricids. The presence of protruded sensilla, observable with the naked eye, is found in the cephalic shields of all species belonging to the genus
Natrix. The identification of these
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Among European colubroids, scale sensilla—mechanoreceptors present in the head integument—are more expressed in natricids. The presence of protruded sensilla, observable with the naked eye, is found in the cephalic shields of all species belonging to the genus
Natrix. The identification of these sense organs in this genus determines its correlation in aquatic and semi-aquatic species, in which these traits are more developed and recognizable than in terrestrial species. As hypothesized for elapoids, this differentiation could be due to the fact that in natricids, like sea snakes, these can perform a hydrodynamic function in addition to the mechanosensory one. In support of this thesis, within the genus
Natrix, the most aquatic species of the five,
Natrix tessellata, features the most expressed sensilla. This specificity represents a further analogy in the evolutionary convergences involving the cephalic region that this species shares with marine elapids. Still in the genus
Natrix, a second trait involving the shields has been identified, expressing itself in the opposite condition to the protruded sensilla, occurring as a pitting arranged mainly within the shields along the upper portion of the labial arches. In vivo examinations and microscopy were performed on different species of the
Natrix genus, and comparative analyses have been carried out on other natricid taxa from the New and Old World, where the presence of protruded scale sensilla has been found in several species.
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