Morphological Adaptations for Shell Anchoring in Calcinus tibicen : Insights From µCT Imaging, Histology and Scanning Electron Microscopy

Hermit crabs rely on external shells for protection due to their non-calcified pleons. This study focuses on the anatomical features and functional roles of various appendages in Calcinus tibicen to understand their mechanisms for shell anchoring. Using scanning electron microscopy (SEM), histological analyses and micro-computed tomography (µCT), we examined the morphology and internal structure of the fourth and fifth pereopods, telson, and uropods. SEM revealed that the pereopods are equipped with scale setae and teeth, which facilitate a firm grip on the shell's internal surface. µCT imaging showed that the uropods play a critical role in gripping the shell, with the left uropod exhibiting more developed musculature. Histological analysis showed that the muscles of the tailfan are striated and also revealed the presence of connective, hemolymphatic and, epithelial tissues. These findings enhance our understanding of the morphological adaptations that facilitate shell use in hermit crabs, emphasizing the importance of both external and internal structures in maintaining grip and stability. This study fills gaps in the literature regarding the role of the tailfan and pereopods in hermit crab shell anchoring, suggesting that uropods function as hooks, and the fourth and fifth pairs of pereopods act as supporting structures.