Studying cuticle shedding in three species of leeches (Hirudinea, Annelida)

Abstract

The renewal and shedding of hard ectodermal structures are widespread in invertebrates. The most impressive example of these processes in Trochozoa is the cuticle shedding observed in Hirudo medicinalis, originally studied over a century ago. Here we investigate cuticle shedding across three leech species: Hirudo sp., Haemopis cf. sanguisuga, and Erpobdella cf. octoculata. According to the ultrastructural data, all three species have a typical leech cuticle, consisting of basi- and epicuticles. Using in vivo observations and morphological investigations, we confirm cuticle shedding in Hirudo sp., and for the first time, report this process in Haemopis cf. sanguisuga. The successive stages of shedding of the old cuticle and formation of the new cuticle are ultrastructurally described for both species. Interestingly, individuals of Erpobdella cf. octoculata did not shed their cuticle during the entire observation period, neither as adults nor as juveniles. The semi-terrestrial lifestyle and the consumption of large food volumes may possibly be a prerequisite driving the development of regular cuticle shedding in Hirudo sp. and Haemopis cf. sanguisuga.