Observations on land-snail shells in near-ultraviolet, visible and near-infrared radiation

The shells of a broad range of land snails were digitally imaged in the near-ultraviolet (NUV), visible range (VIS) and near infrared (NIR). NIR images were recorded in both incident and transmitted illumination. In most cases, shell and periostracal pigmentation observed in the VIS was completely translucent in the NIR, while its contrast was enhanced in the NUV. Exceptions to the above rule fit into four main categories. (1) Snails with green or tan shells or periostraca, presumably functional as camouflage among vegetation, were often highly absorbing in the NUV, thus matching the optical characteristics of green vegetation in this range. (2) Pigmented spiral stripes in the shells of several Camaenidae and Helicidae were adjacent to nonpigmented areas that display a heightened reflectivity and reduced translucence in the VIS and NIR. This enhanced the contrast of the colour pattern in the VIS, but appeared to lack functions in the NIR. (3) Snails from arid or desert environments exposed to high levels of sunlight often have largely white shells, highly reflective throughout the studied range of wavelengths. This is likely an adaptation to reduce the thermal effects of solar irradiation, and may also be a form of masquerading camouflage. (4) Among numerous Bradybaenidae and a few Camaenidae, Helicidae, Orthalicidae and Enidae, reflective patches or stripes, white in the VIS, were present in the periostracum or outermost shell layer. These structures were highly reflective (and highly opaque to transmitted radiation) across the NUV, VIS and NIR. They may have a dual function as disruptive camouflage in the NUV and VIS, and as reflectors to reduce the thermal effects of solar irradiation in the VIS and NIR.