Cuticular adaptations in two parasitic copepods in relation to their modes of life

Abstract

The structure, histochemistry, and possible functional properties of the cuticle in two parasitic copepods Pennella elegans Gnanamuthu and Caligus savala Gnanamuthu have been studied: the former is partially embedded in the host while the latter is an ectoparasite capable of free swimming. In Pennella elegans the cuticle of the embedded anterior region of the body is soft, colourless, and lacks an outer epicuticle while that of the posterior exposed part is pigmented and hard. Conspicuous in the cuticle of the ventral region of the head are pore canals which, though not chitinized, are functional even in the intermoult stage: these canals may be involved in the transport of nutrient materials from the host. The horns, which serve to fix the parasite firmly in the host tissues, are covered by cuticle in which the epicuticle and outer layers of the procuticle are hardened by formation of disulphide linkages. The cuticle of the neck region is not hardened and the procuticle in this region shows transverse regions of dense and light zones probably related to the coiling of the neck during penetration. The epicuticle is two layered in the cuticle of the exposed posterior region, the inner epicuticle and outer region of the procuticle being partially hardened by phenolic tanning so confer rigidity and resistance. The cuticle of the plumes is soft and devoid of an outer lipid epicuticle and so possibly adapted for a respiratory function. In Caligus savala, the epicuticle is two layered, and the procuticle has pigmented, calcified, and uncalcified layers. The cuticle is hardened by phenolic tanning as well as by calcification thus recalling the cuticular organization of decapod crustaceans.