Photoreceptors of cubozoan jellyfish |
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Authors: | Martin Vicki J |
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Institution: | (1) Department of Biology, Appalachian State University, Boone, NC 28608, USA |
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Abstract: | The anatomically sophisticated visual system of the cubozoan jellyfish Carybdea marsupialis is described. Individual cubomedusae have eight complex eyes, each with a cornea, lens, and retina of ciliated photoreceptor
cells, eight slit ocelli, and eight dimple ocelli. The photoreceptor cells of the complex eyes are bipolar and resemble vertebrate
rod cells. Each photoreceptor has an outer cylindrical light-receptive segment that projects into a vitreous space that separates
the lens and the retina, an inner segment rich in pigment granules, and a basal region housing the nucleus. The outer segment
is a modified cilium with a 9 + 2 arrangement of microtubules plus stacks of membrane. These stacks of membrane form numerous
discs that are oriented transversely to the long axis of the cell. The outer segment is connected to the inner segment by
a slender stalk. The basal end of each photoreceptor forms an axon that projects into an underlying layer of interneurons.
Each ocellus is composed of ciliated photoreceptor cells containing pigment granules. Rhodopsin-like and opsin-like proteins
are found in the membrane stacks of the outer segments of the photoreceptors of the complex eyes. An ultraviolet-sensing opsin-like
protein is present in the inner segments and basal regions of some of the photoreceptors of the complex eyes. Rhodopsin-like
proteins are also detected in the photoreceptors of the slit ocelli. The cellular lens, composed of crystallin proteins, shows
a paucity of organelles and a high concentration of homogeneous cytoplasm. Neurons expressing RFamide (Arg-Phe-amide) comprise
a subset of interneurons found beneath the retinas of the complex eyes. RFamide-positive fibers extend from these neurons
into the stalks of the rhopalia, eventually entering into the subumbrellar nerve ring. Vision may play a role in the navigation,
feeding, and reproduction of the cubomedusae. |
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Keywords: | Carybdea marsupialis Cubozoa eyes ocelli |
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