NUCHAL ORGANS OF THE POLYCHAETE PARAPIONOSYLLIS MANCA (SYLLIDAE)

摘要

Nuchal organs are known to be important sensory organs of many polychaete annelid species. This study describes the fine structure of the nuchal organs and associated glands of Parapionosyllis manca. In each nuchal organ, the ciliated epithelium of the nuchal cleft encloses an olfactory chamber through which sensory cilia and microvillus-like processes radiate. These sensory components originate from bulbs of sensory cells that are closely associated to form a sensory bundle. Each bundle of cells is encased in a palisade of support cells bearing motile cilia. Numerous secretory vesicles occur in the cytoplasm of the support cells and beneath the modified cuticle of the nuchal organ. The support cells of the olfactory region extend posteriorly to form the nuchal lobes, or glands. The cells are elongate and taper to a thin neck just before leaving the sensory area of the nuchal organ. There are essentially no nuclei in the sensory region as these and most of the other cellular organelles are concentrated in the lobes that extend into the body cavity but are contained by the epidermal basement matrix. The nuchal organ is innervated by the nuchal nerve, which extends posteriorly from the hind portion of the brain. [References: 31]