Last updated: September 8, 2025
Article
New Species of Eyeless Crustaceans Discovered Near Busy City Streets
We still know little about the myriad forms of life just below our feet, even in highly urban areas, and what we could learn from them.
By David C. Culver, Mikaila Milton, and Elizabeth Burch
About this article
This article was originally published in the "Features" section of Park Science magazine, Volume 39, Number 2, Summer 2025 (August 29, 2025).
Niemiller and others. 2024. A new species of Stygobromus Cope, 1872 (Amphipoda, Crangonyctidae) from a hypotelminorheic seepage spring in Washington, D.C., USA. Subterranean Biology 48: 117-146.
If you’ve walked in the woods in the eastern U.S. in spring or fall, you may have noticed small wet spots, usually no more than a foot in diameter. They lie in shallow depressions, lined with blackened leaves.
What you may not know is they hide a world of tiny animals, whose importance may be greater than we can imagine. These distinctive, semi-permanent wet spots were first described in the scientific literature in the 1960s by the Croatian biologist, Milan Meštrov. He wrote about some from the Medvednica Mountains near Zagreb, Croatia.
But they’re also a common feature of many broad-leafed temperate forests in North America and Europe. They drain a unique underground aquatic habitat, which Meštrov named the “hypotelminorheic.” It consists of small underground basins perched on a layer of clay, usually only about three feet deep. The water flowing out of one of these basins is typically called a seep or seepage spring.
These wet spots harbor highly specialized types of isopods and amphipods—crustaceans distantly related to common pill bugs and shrimp. Such seepage spring specialists are useful little animals. One of the services they provide is to purify shallow groundwater by consuming dead and decaying plant and animal material (detritus). They’re tiny, no bigger than a grain of rice. Like their cave-dwelling counterparts, they have no eyes or skin pigmentation, and they have long legs.
Such seepage spring specialists are useful little animals. One of the services they provide is to purify shallow groundwater.
Since 2012, a team of scientists has collected crustaceans like these from seepage springs in urban national parks in the National Capital Region. We found one new species of amphipod. We also found a new species of isopod in an even more mysterious habitat—a “macropore spring.” We’re studying and checking the other collected specimens against known, described species. Our discoveries show that even small urban parks can harbor species never seen or studied before.
© Jenna Keany. Used by permission.
Professor Matthew Niemiller, an amphipod expert from the University of Alabama, participated in this study. “The discovery of the Anacostia groundwater amphipod and potentially additional species,” he said, “highlights how little we know about the diversity and distribution of life living literally below our feet, even in major metropolitan areas like Washington, DC.”
Sampling When Plants Are Dormant
To collect crustaceans from seepage springs, we first find the springs. Trails aren’t placed according to scientific sampling principles, so they would give us a skewed understanding of the landscape. For this reason, we walk transects spaced at 100-meter—about 328-foot—intervals to locate the seepage springs, rather than using trails.
Trees and other plants draw up much of the water once they leaf out. This causes seeps to dry out, decreasing visible water. And the increased vegetation cover makes seeps hard to find. So we can only sample late in the year, after the trees lose their leaves, or early in the year, before leaves appear.
© William K. Jones. Used by permission.
Between 2012 and 2019, we found and sampled 207 seepage springs. Sixty-six of the springs had amphipods or isopods. We preserved the specimens we collected in absolute alcohol for later examination and DNA analysis.
DNA Analysis Reveals a New Species
Niemiller and his colleague, Professor Thomas Sawicki, examined the morphology (features like shape and size) and genetics of the new amphipod. Existing identification keys and the morphological features of Stygobromus anacostensis initially led them to conclude it was Stygobromus tenuis potomacus, the Potomac groundwater amphipod. But genetic analysis determined that it is actually a distinct species. They gave it the name “Anacostia groundwater amphipod (scientific name: Stygobromus anacostensis).” It is currently known only to occur in a single seep in parkland adjacent to Shepherd Parkway, in southeast DC. The width of that part of the park is no more than about 60 feet.
© William K. Jones. Used by permission.
What’s more, preliminary DNA sequencing suggests that at least three more new species occupy Greenbelt Park, Baltimore-Washington Parkway, and other land managed by the National Park Service. This is despite all of these species currently keying out to Stygobromus tenuis potomacus.
Preliminary DNA sequencing suggests that at least three more new species occupy Greenbelt Park, Baltimore-Washington Parkway, and other land managed by the National Park Service.
Re-examination of the morphology after DNA analysis yielded small but consistent differences. This shows the importance of complementary morphological and genetic analysis. Most collections have not yet been DNA sequenced. So species that primarily differ genetically rather than morphologically have not been cataloged yet. There is undoubtedly more to discover.
An Origin Puzzle
Several questions about these seepage spring specialists remain. Perhaps the most obvious question is where they go in summer when the springs dry up. One possibility is that they migrate down to the water table, although this is often 30 feet deep or more. It’s a challenge for such small, soft-bodied creatures to move through so much soil and rocks. Another possibility is that they burrow into the clay layer beneath the perched groundwater habitat they inhabit during the winter months. Stygobromus readily burrows into clay in the lab, indicating that retreat into this layer is feasible for the little creatures as temperatures rise.
At first, we thought that the amphipods and isopods in seeps were washed out of their primary underground habitat. But detailed studies suggest they actively feed at seepage springs. And the springs have more food than the subterranean layer, which is in total darkness and hence without green plants. It’s hard to directly answer the question of where they came from, because we cannot access the underground habitat without completely destroying it. Our specimens all come from seepage springs.
It’s hard to directly answer the question of where they came from, because we cannot access the underground habitat without completely destroying it.
Another question that has only partially been answered is why they’re located in some seepage springs but absent in others. LIDAR, which uses lasers to map the landscape, showed that seeps with Stygobromus tended to be where the tree canopy is higher. A higher canopy suggests a deeper leaf and detritus layer, the major source of food for the seep dwellers. So perhaps they’re following their food source to sites with a larger overhanging canopy.
There’s also evidence that seepage spring specialists form metapopulations. A metapopulation is a group of dispersed but interacting populations of the same species. When a local population goes extinct, some of its individuals may still inhabit the other populations. That helps keep the species alive. We sampled 12 seepage springs in the Goldmine Tract in C&O Canal National Historical Park in 1994–1995 and again in 2023. During this period, three of four old populations persisted, and one went extinct. Eleven new populations and one new seepage spring appeared. These migrations and extinctions indicate the presence of a metapopulation structure. Without such dispersal, there would be little colonization, leaving the species vulnerable to extinction.
Hidden Habitats and Enigmatic Animals
During our studies, we came across a type of underground habitat even more rare and elusive than the hypotelminorheic. At a couple of sites, we found water seeping out of eroded stream banks of sand and gravel. Wedged between two layers of this soil was this other type of shallow groundwater habitat, the surface manifestation of which is called a macropore spring.
In Fort Belvoir, a large army base nearby, there’s a unique amphipod in this kind of habitat. It’s called Stygobromus phreaticus, or the Northern Virginia amphipod. It was originally found in shallow wells in Vienna and Alexandria, Virginia. But it hasn’t been found in wells since 1948, as shallow wells have been filled in, and the regional water table has dropped. At present, this amphipod is only known to inhabit the Fort Belvoir site.
© David Culver. Used by permission.
We can only access this highly unusual subterranean habitat through eroded streams. This is because the water from this habitat usually exits directly into a stream. Nevertheless, we were very fortunate to discover specimens of a new isopod species, Conasellus washingtoni, or Washington’s groundwater isopod, in a macropore spring. The spring was in the Civil War Defenses of Washington, a National Park Service unit. The site was near a major road, Pennsylvania Avenue Southeast. This is the only eyeless, unpigmented isopod that has ever been found in the Washington, DC, region.
Macropore springs and their inhabitants remain enigmatic. But this type of shallow subterranean habitat is likely more common than the few examples would suggest. This is because there are few access points to this habitat, and few biologists have looked for them. Shallow wells are basically nonexistent in densely populated areas. Eroding streams are becoming less common as communities and landowners reinforce stream banks for stormwater management.
We were very fortunate to discover specimens of a new isopod species, Conasellus washingtoni, or Washington’s groundwater isopod, in a macropore spring.
Previous records indicate that other kinds of animals may also frequent macropore springs. Modern techniques like environmental DNA (DNA found outside organisms, such as in water or soil) may enable us to find even more uncanny creatures living in these hidden habitats. Apart from the wonder they generate, who knows what we could learn from knowing more about the species found in macropore springs.
Out of Sight but Still Important
When people think of exotic or strange invertebrate animals, they may not think of them as residing in urban “pocket” parks or highway medians. But our work shows that such creatures nonetheless exist in those settings. Protecting urban habitats can pose special problems. The Baltimore-Washington Parkway is subject to change and development, jeopardizing the existence of the new amphipod we found there. The new isopod species is under threat from the very forces that exposed it—stormwater and erosion.
Seepage springs and macropore springs are easily overlooked. Landscape modifications, trail construction, or tree removal may inadvertently damage them. Even foot traffic, which compacts the soil, can destroy them. The rare species they contain are seldom listed for protection under the Endangered Species Act of 1973. That doesn’t, however, invalidate their importance.
“These discoveries demonstrate that small urban parks are not just for recreation but can play a vital role in conservation,” said John Paul Schmit, a quantitative ecologist with the National Park Service. “Urban parks can preserve older forests and unique habitats that may not be well protected elsewhere.”
About the authors
David C. Culver is an environmental science professor at American University in Washington, DC. Image courtesy of David C. Culver.
Mikaila Milton is a biologist with the National Park Service, National Capital Parks-East. Image courtesy of Mikaila Milton.
Elizabeth Burch is an instructor in the Environmental Science department at American University. Image courtesy of Elizabeth Burch.
Cite this article
Culver, David C., Mikaila Milton, and Elizabeth Burch. 2025. “New Species of Eyeless Crustaceans Discovered Near Busy City Streets.” Park Science 39 (2). August 29, 2025. https://www.nps.gov/articles/000/psv39n2_new-species-of-eyeless-crustaceans-discovered-near-busy-city-streets.htm