Fine structure and ecdysis of mandibular sensilla associated with the lacinia mobilis in Neomysis integer (Leach, 1814) (Crustacea, Malacostraca, Peracarida)

•Mandibles of adult Neomysis integer were studied using light and electron microscopy.•We describe the external and internal structure.•Special reference is paid to the lacinia mobilis and characteristics of the ecdysis.•Present sensory cells reveal that both laciniae mobiles are mechanosensory organs.•Discussion of the classification and a possible homology in Peracarida and Decapoda.

The external and internal structures of adult Neomysis integer mandibles were studied using light and electron microscopy with special reference to the lacinia mobilis, a highly specialized appendage on the gnathal edge of many crustaceans. The right and left lacinia mobilis are equipped with ciliary primary sensory cells revealing that both laciniae are also mechanosensory organs in addition to their mechanical function during mastication. A detailed character analyses indicated that the right lacinia is probably a highly derived sensory seta, whereas two alternative interpretations are considered for the left lacinia; it could be a sensillar appendage equipped with two mechanosensory units, or it could be a movable appendage of the incisor process containing two sensilla deprived of external appendages. The ecdysis of the lacinia mobilis corresponds very well to type I sensillar ecdysis, suggesting classification as a sensillar appendage. These features support a possible homology of the right lacinia mobilis in Peracarida and Decapoda, tracing them to an origin as a member of the setal row. Whether the left lacinia mobilis is a sensillum or an appendage with sensilla cannot be resolved presently.