Earlier detailed studies of cnidarian planula larvae have revealed a simple nervous system but no eyes or identifiable light sensing structures. Here, we describe the planula of a box jellyfish, Tripedalia cystophora, and report that these larvae have an extremely simple organization with no nervous system at all. Their only advanced feature is the presence of 10-15 pigment-cup ocelli, evenly spaced across the posterior half of the larval ectoderm. The ocelli are single cell structures containing a cup of screening pigment filled with presumably photosensory microvilli. These rhabdomeric photoreceptors have no neural connections to any other cells, but each has a well-developed motor-cilium, appearing to be the only means by which light can control the behaviour of the larva. The ocelli are thus self-contained sensory-motor entities, making a nervous system superfluous.
|Number of pages||6|
|Journal||Proceedings of the Royal Society B: Biological Sciences|
|Publication status||Published - 22 Nov 2003|
- Chironex fleckerii
- Chiropsalmus sp.
- Pigment-cup ocelli
- Rhabdomeric photoreceptor
- Tripedalia cystophora