Helobdellids

Helobdela group

Helobdella lineata

Mark E. Siddall *



___.___.___ Desmobdella paranensis
   |   |___.___ Helobdella stagnalis
   |       |___ Helobdella stagnalis
   |___.___ Helobdella elongata
       |___.___ Helobdella fusca
           |___.___ Helobdella lineata
               |___.___ Helobdella transversa
                   |___.___ Helobdella papillata
                       |___.___ Helobdella triserialis triserialis
                           |___ Helobdella triserialis papillata

Based on: CO-I, ND-1, and morphology in Light and Siddall, 1998

Discussion of Relationships

Insofar as H. stagnalis is the type species of the genus Helobdella, this genus probably should include species of Desmobdella as well (Fig. 3). Phylogenetic data also clarified relationships between Helobdella triserialis, H. papillata, H. lineata, and H. fusca. These species previously have been noted as problematic (Appendix I). Helobdella papillata, H. lineata, H. triserialis, and to some extent H. fusca are similar in appearance (Fig. 7). By way of example, the specimen denoted Helobdella triserialis papillata possessed many of the traits characteristic of H. triserialis sensu stricto, but it also possessed black-tipped papillae, a trait characteristic of H. papillata but not H. triserialis. Despite distinct descriptions of these two species, phylogenetic data supports a close relationship between H. papillata and H. triserialis (Fig. 3). Three extra steps would be necessary to form a monophyletic group of H. lineata, the H. triserialis species, and H. papillata. Sawyer (1986) suggested that Helobdella lineata is the same species as H. triserialis. Phylogenetically, though, the more distinct H. transversa clearly separates H. lineata from the H. triserialis species group. It requires an additional 15 steps to form a monophyletic clade consisting of only H. lineata and the H. triserialis species. Still others have synonymized Helobdella lineata with Helobdella fusca (So—s, 1969; Sawyer, 1986). Helobdella lineata clearly does resemble Helobdella fusca more than it does H. triserialis as both possess longitudinal pigmentation. Their positions on the cladogram suggest that this is a plesiomorphic similarity as opposed to evidence of a close relationship. It would require 41 extra steps for H. lineata and H. fusca to be a monophyletic group. Despite identification problems regarding individual species, the genus Helobdella is monophyletic if one includes the Desmobdella species, contra Soós (1969) who believed that the genus Helobdella was a "very heterogeneous genus." All Helobdella species have one pair of eyes and they all are non-blood-feeders.

Helobdela group

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