A review of the genus Eclipidrilus (Annelida: Clitellata: Lumbriculidae), with description of a new species from western North America

Eclipidrilus pacificus n. sp., from northwestern USA, is distinguished from other Eclipidrilus by having a single atrium with midventral male pore, small penis, prostomium without a proboscis, and non-spiraling atrial musculature. Most populations also differ from congeners in having paired spermathecal pores anterior to the ventral chaetae, but specimens from the Columbia River have variable number and placement of the spermathecae. An unusual spiral orientation of the atrial musculature has previously been used to define Eclipidrilus. However, orientation of the atrial muscle layers varies among the previously described species, and does not provide a distinctive synapomorphy for the genus as a whole. Consequently, the genus is redefined to include species having elongate-petiolate atria with an inner, near-transverse muscle layer and an outer, longitudinal to spiral muscle layer.