The marine gastropod Conomurex luhuanus (Strombidae) has high-resolution spatial vision and eyes with complex retinas

Abstract

All species within the conch snail family Strombidae possess large camera-type eyes that are surprisingly well-developed compared to those found in most other gastropods. Although these eyes are known to be structurally complex, very little research on their visual function has been conducted. Here, we use isoluminant expanding visual stimuli to measure the spatial resolution and contrast sensitivity of a strombid, Conomurex luhuanus. Using these stimuli, we show that this species responds to objects as small as 1.06{degrees} in its visual field. We also show that C. luhuanus responds to Michelson contrasts of 0.07, a low contrast sensitivity between object and background. The defensive withdrawal response elicited by visual stimuli of such small angular size and low contrast suggests that conch snails may use spatial vision for the early detection of potential predators. We support these findings with morphological estimations of spatial resolution of 1.04 {+/-} 0.14{degrees}. These anatomical data therefore agree with the behavioural measures and highlight the benefits of integrating morphological and behavioural approaches in animal vision studies. Furthermore, using contemporary imaging techniques including serial block-face scanning electron microscopy (SBF-SEM), in conjunction with transmission electron microscopy (TEM), we found that C. luhuanus have more complex retinas, in terms of cell type diversity, than previous studies of the group have discovered using TEM alone. We found the C. luhuanus retina is comprised of six cell types, including a newly identified ganglion cell and accessory photoreceptor, rather than the previously described four cell types. Summary statementBehavioural trials indicate the eyes of conch snail species Conomurex luhuanus provide high-resolution spatial vision, and morphological examination reveals the retina contains more cell types than those of other gastropods.