Discovery of a Novel Accessory Structure of the Pitviper Infrared Receptor Organ (Serpentes: Viperidae)

Abstract

The facial pits of rattlesnakes, copperheads, lanceheads, bushmasters and other American and Asian pitvipers (Crotalinae) are highly innervated and densely vascularized infrared (IR) receptor organs. For over a century, studies have focused on a small sample of model species from North America and Asia. Based on an expanded survey of Central and South American crotalines, we report a conspicuous accessory structure composed of well-defined papillae that project from the anterior orbital adnexa. The papillae are continuous with the inner chamber of the IR receptor organ and our histological and ultrastructural data suggest that they possess a well-developed nervous network and extensive vascularization; however, they lack the characteristic IR-sensitive terminal nerve masses found in the IR-receptive pit membrane. The function of the IR receptor organ papillae is unknown.

Eye and pit size are inversely correlated in crotalinae: Implications for selection pressure relaxation

“…The facial pit consists of a flask-shaped cavity divided into inner and outer chambers by a suspended sensory membrane which is obviously larger than the cavity mouth (de Cock Buning, 1985;Gracheva et al, 2010). The inner chamber opens near the ipsilateral eye with a small tunnel (Bol ıvar-G et al, 2014). The cavities expand into a depression of the maxillary bone.…”