Helobdella blinni sp. n. (Hirudinida, glossiphoniidae) a new species inhabiting montezuma well, Arizona, USA

A new leech species Helobdella blinni sp. n., is described from Montezuma Well, an isolated travertine spring mound located in central Arizona, USA. In its native habitat, H. blinni had been previously identified as Helobdella stagnalis (Linnaeus, 1758), which was later reclassified to Helobdella modesta (Verrill, 1872). Similar to the European H. stagnalis and North American H. modesta, H. blinni has six pairs of testisacs, five pairs of smooth crop caecae, one lobed pair of posteriorly-directed crop caecae, one pair of eyes, a nuchal scute, and diffuse salivary glands. However, the pigmentation of this new species ranges from light to dark brown, unlike H. modesta which tends to be light grey in color. Also, H. modesta produces a clutch of 12-–35 pink eggs, whereas H. blinni produces smaller clutches of white eggs (7–14, 0.5 ± 0.15 mm, N = 7) and consequently broods fewer young (1–14, 7 ± 3.3 mm, N = 97). Helobdella blinni are also able to breed year-round due to the constant warm water conditions in Montezuma Well. Their breeding season is not restricted by seasonal temperatures. These species are morphologically similar, however, comparing the COI mtDNA sequences of H. blinni with sequences from nearby populations of H. modesta and other Helobdella species from GenBank indicate that H. blinni is genetically distinct from these other Helobdella populations.