Ocular arrangement and visual acuity were examined in Lycosa leuckartii Thorell 1870 (Araneae: Lycosidae), using histological techniques. Major structural and functional features of the visual system, including external and internal ocular organizations, resolution, sensitivity, focal lengths and the field of view, were characterized for each eye. Lycosa leuckartii had a large developmental investment in a specialized visual system with high visual acuity. The field of view extended 360° and displayed the potential for good depth perception. Anterior eyes showed average focal lengths (AL eyes 230.88 µm, AM eyes 276.84 µm), while the posterior eyes far exceeded them (PL eyes 499.26 µm, PM eyes 675.35 µm). Resolution of the anterior eyes was comparable to records in the literature for other lycosids (inter-receptor angle AL eyes 2.45°, AM eyes 1.85°), while the resolution of the posterior eyes was higher (PL eyes 0.78°, PM eyes 0.67°). Sensitivity of the lens (f-numbers) was highest in the secondary eyes and was close to some of the highest reported for Araneae (f-numbers PM eyes 0.58), but when receptor diameters were included in estimates, S-numbers were similar or lower than closely related species (PL eyes 17.5 µm2, PM eyes 17.6 µm2). There is a clear distinction in organization and function between the posterior and anterior eyes of L. leuckartii. The posterior eyes suit long- range predator and prey detection, while the anterior eyes are best for distance judgment and prey capture.
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Vol. 38 • No. 3