Eye development in the box jellyfish Carybdea marsupialis

Abstract

Cnidarians are the most primitive invertebrates alive today to possess eyes. The complex eyes of the cubozoan jellyfish Carybdea marsupialis exhibit many similarities to the camera-type eyes of higher metazoans including the presence of a cornea, lens, and retina of ciliated photoreceptors. It is these similarities that make understanding the evolution and development of eyes in basal cnidarians important, as they may lead to a better understanding of eye evolution. During the transformation of the polyp to the eye-bearing medusa, the development and arrangement of several components were followed including the neuropeptide FMRFamide, UV opsin-like protein (indicates photoreceptor formation), J1-crystallin (indicates lens formation), and shielding pigment formation. The first ocelli to appear were the complex eyes followed by the simple ocelli; the small complex eye was the first to exhibit pigment formation (melanin) as well as photoreceptor maturation. J1-crystallin was located in the developing lenses/lens-like material in the complex eyes and slit ocelli. Extensive neurological rearrangement and development takes place during the transformation. Developmental mechanisms in eye formation similar to both vertebrates and invertebrates were seen. This study clearly demonstrates the presence of the basic optic molecules and developmental mechanisms in the first multicellular animals possessing complex camera-type eyes.