ULTRASTRUCTURAL ANALYSIS OF THE SENSILLA OF AUSTROPERIPATUS-AEQUABILIS REID, 1996 (ONYCHOPHORA, PERIPATOPSIDAE)

The head of Austroperipatus aequabilis bears five types of sensilla, w hich were examined by electron microscopy. They differ from each other in position, shape of outer sensory elements and cuticular socket str uctures. Thus, we distinguish sensilla with sensory hairs, sensilla wi th sensory bulbs, cone-shaped sensilla, sensilla with sensory bristles , and sensilla of the lips. They are composed of up to 15 cells, which can be separated into four cell types. The most frequent cell type is the bipolar receptor cell that occurs in all sensilla. The apical sur face of this primary receptor cell is characterized by one or two part ly branched cilia with a basal 9 x 2 + 0 pattern of microtubules. A mo dified bipolar receptor cell was found in all sensilla bearing a senso ry peg except for the sensilla equipped with sensory bristles. The api cal dendrite extends to a long pale process which exclusively contains mitochondria and single microtubules. In all sensilla examined in thi s study at least one supporting cell occurs which is characterized by parallel microvilli. An additional function of this cell type as a par t of the stimulus-conducting system is possible. In the sensillum with a sensory bulb two kinds of supporting cells occur. A unique cell typ e with an upside down position has regularly been found in all sensill a bearing a sensory peg. Apart from the sensilla they also occur withi n the labial epidermis. Since most sensilla contain several different receptor cells, they can be considered as complex sense organs. (C) 19 98 The Royal Swedish Academy of Sciences. Published by Elsevier Scienc e Ltd. All rights reserved.