Eyes and vision in the Chengjiang arthropod Isoxys indicating adaptation to habitat

Schoenemann, B. & Clarkson, E.N.K. 2011: Eyes and vision in the Chengjiang arthropod Isoxys indicating adaptation to habitat. Lethaia, Vol. 44, pp. 223–230. The arthropod Isoxys is common in the lower Cambrian Chengjiang biota, but only a few specimens retain details of the eye structure, though the eyes are invariably flattened. One specimen of Isoxys auritus has a pair of large eyes, projecting from the body and showing a flexible eye‐stalk, a discoidal, slightly convex palpebral lobe, and part of the original visual surface upon which lenses can be distinguished. The remarkable preservation allows the eye parameter, sensitivity, and the anatomical acuity of this eye to be established; it was adapted to an environment where the illumination corresponds to that of street light at night, in other words up to ～140 metres depth. This fits well with previous estimates. A second specimen, from a different locality (Mafang), interpreted as a different form, probably a different species, was adapted to more shallow, well‐lit surface waters. □Arthropoda, Cambrian, Chengjiang, ecological niche, Isoxys, vision.