TEM studies on the lattice organs of cirripede cypris larvae (Crustacea, Thecostraca, Cirripedia)

Lattice organs consist of five pairs of sensory organs situated on the dors al carapace in cypris larvae of the Crustacea Cirripedia. The lattice organ s in cypris larvae of Trypetesa lampas (Acrothoracica) and Peltogaster pagu ri (Rhizocephala) represent the two main types found in cirripedes, but onl y minor differences exist at the TEM level. Each lattice organ is innervate d by two bipolar, primary receptor cells. The inner dendritic segment of ea ch receptor cell carries two outer dendritic segments. The outer dendritic segments contain modified cilia with a short ciliary segment (9x2+0 structu re). Two sheath cells envelop the dendrite except for the distal ends of th e outer dendritic segments. This distal end enters a cavity in the carapace cuticle and reaches a terminal pore situated at the far end of the cavity. The cuticle above the cavity is modified. In both species the epicuticle i s partly perforated by numerous small pores and the underlying exocuticle i s much thinner and less electron dense than the regular exocuticle. Lattice organs very probably have a chemosensory function and are homologous with the sensory dorsal organ of other crustacean taxa.