Summary

Much is known about the mechanosensory behaviour of the spider Cupiennius salei Keyserling, but much less about its visual capabilities. In this study the quality of the optical image, the retinal resolution and the fields of view were assessed for each of the four pairs of eyes. The image is of good quality in all eyes. The principal (antero-median) eyes lack a tapetum and have an inter-receptor angle of 2.9°. The three secondary eyes (antero-lateral, postero-median and postero-lateral) all have 'gridiron ' tapeta with receptors arranged in rows. The angular separations (along rows x between rows) are 3.6 ° x 9.3°, 0.9 ° x 2.3 ° and 1.0 ° x 3.0°, respectively. Although the disposition of eyes on the head is similar to that of pisaurid spiders, all other features of the eyes, including the sizes and shapes of the fields of view, resemble those of lycosid spiders. The peripheral visual system of Cupiennius can thus, in principle, support a similar range of visual behaviour to that of lycosids, which includes prey capture, predator avoidance and courtship