Nikolaj A. Livanow (1876 - 1974) and the living relict Acanthobdella peledina (Annelida, Clitellata)

The Clitellates are segmented worms (Annelida) that are characterized by a glandular girdle responsible for cocoon production. They are usually classified as the Oligochaeta (earthworms and allies) and the Euhirudinea (true leeches); these carnivorous clitellates use two suckers for attachment and crawling. In 1850, A. E. Grube discovered a primitive leech with only one (posterior) sucker and earthworm-like cephalic chaetae for attachment to its host. The anatomy of this living relict (Acanthobdella peledina) was described by N. A. Livanow in 1906. Our knowledge of A. peledina is based on Livanow's detailed and comprehensive monograph in which this fish parasite is identified as an ancient hirudinean. In this article we describe the life and major scientific works of N. A. Livanow and summarize his contributions to annelid systematics. We also review the life cycle and phylogenetic position of the connecting link, A. peledina, based on anatomical studies and DNA sequence data. It is concluded that both Livanow's hypotheses concerning the phylogenetic relationships within the clitellata and his interpretation of the living fossil A. peledina were correct. In addition, the second Acanthobdella species, A. livanowi Epshtein 1966, is briefly described and commented on.