Thursday 29 February 2024

Stygobromus anacostensis: A new species of subterranean Amphipod from Washington D.C.

The genus Stygobromus contains 137 described species of Amphipod Crustaceans found in subterranean environments, predominantly in North America. The diversity of this group is particularly high in groundwater habitats of the Piedmont and Atlantic Coastal Plain of Maryland, Virginia, and the District of Columbia, an area from which thirteen species have been described to date, seven from shallow subterranean habitats in the lower Potomac River Basin and the area around Washington D.C. With over 150 identified seepage springs, Washington D.C. is a particularly suitable environment for the study of these Crustaceans, whose known diversity is thought to hide a significant number of cryptic species (species which physically resemble other species, but which are genetically isolated from them).

In a paper published in the journal Subterranean Biology on 15 February 2024, Matthew Niemiller of the Department of Biological Sciences at the University of Alabama in Huntsville, Andrew Cannizzaro of the Department of Biology at Miami University, Thomas Sawicki of the Department of Biological Sciences at Florida Agricultural and Mechanical University, and David Culver of the Department of Environmental Science at the American University, describe a new species of Stygobromus from a hypotelminorheic seepage spring (seepage spring of shallow subterranean origin) at Anacostia Park in metropolitan Washington D.C.

The new species is named Stygobromus anacostensis, where 'anacostensis' means 'from Anacosta' in reference to the place where it was discovered. The species is described on the basis of five specimens collected from a seepage spring that emerges from a small, 2-m high rockface about 5 m from Malcolm X Avenue SE in September and October 2021.

Stygobromus anacostensis, habitus: (A) Holotype male, 5.9 mm (USNM 1606902) (B) Allotype female, 5.3 mm (USNM 1606903). Scale bar is 1 mm. Niemiller et al. (2024).

Stygobromus anacostensis is notable in its small size, with the largest male specimen found measuring 5.9 mm in length while the largest female was only 5.3 mm long. It can be distinguished from all other members of the genus by having two pairs of antennae, with the second pair being clearly shorter than the first, and by blade-like edges to its gnathopods (mouthparts made from modified limbs). A genetic analysis recovered Stygobromus anacostensis as the sister species to Stygobromus potomacus, a species which has also been found in Anacostia Park, as well as in Caledon State Park in Virginia, roughly 100 km to the south.

Stygobromus anacostensisI is known only from a single location, a seepage spting in an urban area. While the site of this spring is on land controlled by the National Park Service, it is close to a major urban thoroughfare, and vulnerable to road salt, as well as any potential drainage improvement work carried out in the area. For this reason, Niemiller et al. recomend that the species be classified as Critically Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species, and given the status of Critically Imperilled under the NatureServe wildlife conservation scheme.

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