A mantis shrimp wearing sun‐glasses

Abstract

Lysiosquillina maculata and L. sulcata have an exceptional mechanism, never observed in any other eye, for adaptation to the extreme light condition in their habitat. The eyes of L. maculata and L. sulcata are similar to, and here compared with those of other stomatopods. But a peculiar, complex system of muscles and veils surrounds the cones. Tight linkages attach this system to the cones and wedges, presumably adapting the eye (or different regions of the eye) to the intensities and angles of incident light. The muscles are also attached to a unique system of sunglasses. Viewing the frontal part of the living eye within a small solid angle, a large part appears black but, with a slight change in the viewing direction, it becomes white, i.e., totally reflecting the light. Corresponding to the reflecting part of the eye, the cornea thickens with two additional layers with varying stratification of alternating refractive indices. In this part, a thin layer of a particular tissue is inserted into the cornea and attached to the muscles containing transparent veils that surround the cones. Here the cones are not attached directly to the cornea, but to this tissue, which is composed of an outer lining underlying the cornea, containing many nuclei and many branching strands at the proximal side. The interior is composed of fibrous structures approximately parallel to each other and to the cornea, presenting aligned granules or crystals and cytoplasmic strands connected to the veils. In bright light, the additional cornea layers and the peculiar tissue likely reflect the light with total internal or external (depending on the angle of incident light) reflection. The muscles subserve light‐ and dark‐adaptation. During the day, within a small solid angle, a large part of the frontal ommatidia are screened off from the bright light. During the night, presumably also the frontal ommatidia become operant, due to the contraction of the muscles which alter the optics of the eye.

Key words:

• Stomatopods
• Vision
• Total reflection
• Adaptation
• Muscles between cones