PHOTOMECHANICAL RESPONSES IN THE EYE OF THE JAMAICAN FRESHWATER SHRIMP MACROBRACHIUM HETEROCHIRUS(WIEGMANN)

Abstract

Dark/light adaptational changes in the eye of the Jamaican freshwater shrimp Macrobrachium heterochirus involves distal and proximal pigment migrations as well as changes in cellular shapes. A small lens-like structure at the distal tip of the rhabdom is described for the first time in a shrimp. Rhabdoms are enlarged at night. Individuals are usually nocturnal and it is believed that under dim light conditions, larger crabs have a double-advantage over small ones: not only are they stronger: they also see better in the dark. It is finally suggested that tapetal cells may respond directly to light without hormones getting involved.