Regional differentiation of the cuticular surface structure in the mesoparasitic copepod Cardiodectes shini (Siphonostomatoida: Pennellidae) on a pygmy goby

Abstract

Cardiodectes shini is a mesoparasitic copepod found on the heads of pygmy gobies. The copepod inserts its cephalothorax with antennary processes into the host tissues, while the trunk and egg sacs remain outside the host. The ultrastructure of the epicuticle surface differs among the antennary processes, cephalothorax, and trunk. In the antennary process, the epicuticle appears fuzzy and is less electron-dense than other parts of the body. This loose cuticle structure may be related to the absorption of nutrients in the host hemolymph. The cephalothorax and trunk have an electron-dense epicuticle: there is an array of minute protuberances on the epicuticle of the cephalothorax, whereas the trunk cuticle has no protuberances. This array of protuberances might be involved in suppression of the host immune response, because the cephalothorax has direct contact with the host connective tissues and similar structures are found on other parasitic copepods inhabiting host tissue.