New genus of Lumbriculidae (Annelida, Clitellata) from a karst spring in the Cantabrian Mountains, northern Spain.

The groundwater worms of the family Lumbriculidae exhibit high diversity and endemism in southern Europe. All stygobiont lumbriculid species known so far in this region belong to six genera. In the present study, a new stygobiont lumbriculid Fendia cantabrica n. gen. n. sp. is described, mainly based on distinct characteristics of the male duct structure. The male duct is semiprosoporous and the spermathecae (two pairs) are postatrial, starting in the ovarian segment. These characteristics are shared with only two lumbriculid genera: the Nearctic Eremidrilus and Holarctic Trichodrilus. The new genus is clearly distinguished from the former by the absence of proboscis, and from both genera by a remarkably complex structure of the atrium: a very strong musculature organized in several crossed layers, a protrusible penis with a singular hydrostatic skeleton, and two prostate glands, which join separately to the atrial ampulla by short stalks.