White in color, measured in millimeters, and eyeless, the small Hay's Spring amphipod has been making a big splash in talks over the purple line. The shrimp-like creature could possibly change the course of the project.
Some environmentalist say the endangered species has been found in parts of Rock Creek in the District, and could also be living in Montgomery County, near the path of the rail line.
"They're indicators of the freshest, purest water we have, the kind that comes from natural springs and in this case, Rock Creek," said attorney and environmental advocate John Fitzgerald.
People like Fitzgerald want to make sure the crustaceans stay protected in other areas, and especially from the 16-mile light rail project that will stretch from Bethesda to New Carrollton.
"The Hay's Spring amphipod is right downstream from here and they didn't think 'Oh, the dirt the runoff, the hazardous waste sites right by here' may pollute the habitat," said Fitzgerald.
A review funded by the U.S. Fish and Wildlife Service several years ago mentioned no federally endangered species near the purple line boundaries.
But that's not stopping groups from wanting officials to take a closer look at their concerns.
"Which means doing a precise study of these species and asking the Fish and Wildlife Service whether that shows that it will not jeopardize the continued existence or recovery of these species," said Fitzgerald.
"There is a process and it's an important process. But we followed it, and opponents of the purple line are primarily motivated by delaying the line," said Purple Line Now! Secretary Gregory Sanders.
Sanders is part of a coalition of community members who say the project needs to move forward.
"The longer we delay...the more poor land use, and warming from cars, and the like, can proceed," said Sanders.
But another roadblock could be in the courtroom.
"The next step is also to file a 60-day notice with intent to sue, to make sure everybody knows that there's an issue that has to be dealt with," said Fitzgerald.
The $2.2 billion dollar purple line is set to break ground in 2015, with an opening date of 2020.