Ultrastructure of the frontal sensory fields in the Lynceidae (Crustacea, Branchiopoda, Laevicaudata)

The clam shrimp family Lynceidae is unusual in possessing paired fields of short setae on either side of the rostral carina. We describe the position of these fields relative to the direction of water movement in live animals as well as the external and internal structure of these setae. The majority of morphological features support a presumed chemosensory role for these sensilla. These features include the lack of a setal socket and the relatively short length of each seta. The low number of enveloping cells (three or four) is uncharacteristic of chemosensory setae and is more typical of mechanoreceptors, as is the absence of any pores on the setae; these characteristics indicate that these fields may have both functions. © 1994 Wiley‐Liss, Inc.