Ultrastructure of mandibular organ in the male fiddler crab, Gelasimus hesperiae (Crane, 1975) at normal and induced moult cycle stages

• Aishwarya Nath, Sudha Kappalli, and Bhadravathi Kenchappa Chandrasekhar Sagar

This study examined the morphology and ultrastructure of the mandibular organ (MO) in male fiddler crab, Gelasimus hesperiae, at normal moult cycle as well as induced moult cycle stages through bilateral eyestalk ablation. At normal moult cycle stages, MO exhibited significant morphometric changes with maximum size during the premoult stage ($\mathit{P}\mathrm{<}0.05$). Light and electron microscopy of the tissue revealed three distinct cell types designated as A, B and C cells, but the presence of C cells was noticed only during the premoult. At population level, A cells are relatively more abundant at intermoult stage (80.64%) ($\mathit{P}\mathrm{<}0.05$) but at premoult and postmoult, B cells predominated. At mid-premoult stage the cytoplasm of B cells and C cells, showed the rich presence of numerous polymorphic mitochondria and endoplasmic reticulum. C cells are relatively more electron dense. Specifically, the nuclei of B cells appeared with cytoplasmic inclusions containing mitochondria, ribosomes, polysomes and endoplasmic reticulum. Removal of eyestalk hormones through bilateral eyestalk ablation accelerated the moulting along with the structural distortion of the MO as evidenced from the present light and electron microscopic details. To conclude, the present study reveals that MO in the male fiddler crab, Gelasimus hesperiae plays a crucial role in its normal moulting and eyestalk hormones are necessary for maintaining the structural integrity of the MO in this species.