Aspects of the functional anatomy of the eyes of the whip-scorpionThelyphonus caudatus(Chelicerata: Arachnida) and a discussion of their putative performance as photoreceptors

Abstract

Abstract T. caudatus reacts to light with a momentary locomotory arrest. Two frontal ( = median) eyes each 370 μam in diameter, and a cluster of three small lateral eyes on either side of the prosoma are present. Each frontal eye possesses a large biconvex lens that produces a clear image approx. 200 μm behind the inner surface of the lens. This is compatible with an optically homogeneous lens of 1.51 refractive index. The retina of the frontal eye is eversc, and groups of predominantly three retinula cells, held together by desmosomes, give rise to centrally fused rhabdoms up to 20 μm wide. A tapetum is not developed in the frontal eye, but screening pigment granules are present; these remain in a dark-adapted position even when the eyes are fixed in daylight between 0700 and 0800 hr. Lateral eyes strongly reflect light because of a well developed tapetum. Although distally, clusters of mostly three cells resemble similar groups found in the frontal eyes, the retina of the lateral eye is reticulated and ...