Description of the Californian leech Helobdella robusta sp.nov., and comparison with Helobdella triserialis on the basis of morphology, embryology, and experimental breeding

Abstract

This paper describes the leech Helobdella robusta, which was collected from the Sacramento delta of California. This new species is generally similar to another species found in California, Helobdella triserialis, and the two were compared in detail. In the adult, we observed reliable differences in the relative dimensions of the body, the size of the dorsal papillae, the pattern of cutaneous pigmentation, and the structure of the gut. In the embryo, we observed differences in the appearance of the yolk platelets and the size of the adhesive gland. We also observed differences in the rate of embryonic development. All of these differences persist in breeding populations that have been maintained in the laboratory over many generations. Experimental studies indicate that H. robusta and H. triserialis have little or no proclivity for interbreeding, supporting their distinction as separate species.