Structure of the mouth tube of a parasitic copepod,Isobranchia appendiculata Heegaard, 1947 (Siphonostomatoida:Lernaeopodidae)

The structure and musculature of the mouth tube of the lernaeopodidIsobranchia appendiculata Heegaard is described in detail. Situated on the median eminence, the mouth tube appears to be lodged inside a median longitudinal groove on the ventral wall of the cephalothorax. The components of the mouth tube, the labrum and the labium are loosely held together along their lateral edges. The thin, transparent walls of both the labrum and the labium are reinforced by chitinous rods. The musculature of the mouth tube consists of two pairs ofretractores oris, four pairs ofcompressores labri and two pairs oflevatores labii. The mandibles are operated by a pair of antagonistic muscles, theroto adductor mandibulae androto abductor mandibulae. Like other lernaeopodids,I. appendiculata resorts to a browsing type of feeding.