A Phylogeny of Marstonia lustrica (Pilsbry 1890) (Gastropoda: Hydrobiidae) Across its Range Thomas W. Coote* Abstract - Marstonia lustrica is a poorly understood aquatic snail, relatively rare throughout its range, and listed in the State of Massachusetts as endangered. It is the northern-most cold temperate species of its genus, with other members of the genus occurring along the southern edge of its range and in the southeastern United States. The current range of M. lustrica appears to follow the maximum extent of the Laurentide Glacier (20–25 kya), extending from Minnesota to western Massachusetts. Historically the northern Marstonia species have been identified as M. lustrica with a few historical populations of M. scalariformis and M. letsoni on the southern edge of its range. I completed a full range survey of M. lustrica in 2007 and 2008 and sampled over 60 waterbodies with populati ons identified in 20 lakes or rivers from Minnesota east to Massachusetts, and Ohio north to Ontario, Canada. Fifty-seven specimens from the 20 populations were sequenced for 2 mtDNA markers (COI and NDI). 14 concatenated haplotypes were documented across the range.