Piedmont Groundwater Amphipod

Stygobromus tenuis (S. I. Smith, 1874)

Stygobromus tenuis (Smith 1984)

Malacostraca (Malacostracans)
Crangonyctidae (Gammarid Amphipods)
State Protection
Not Listed
Not listed or protected by New York State.
Federal Protection
Not Listed
State Conservation Status Rank
Not Ranked - State conservation status not yet assessed.
Global Conservation Status Rank
Apparently Secure globally - Uncommon in the world but not rare; usually widespread, but may be rare in some parts of its range; possibly some cause for long-term concern due to declines or other factors.


Did you know?

The Piedmont Groundwater Amphipod is a cave and groundwater dwelling crustacean. To adapt to this dark, underground habitat they are unpigmented, have attenuated bodies, and are eyeless (Culver 2012).

Conservation and Management

Conservation Overview

The Piedmont Groundwater Amphipod is one of only two naturally occurring amphipods in New England. This species is limited to karst geology, therefore it may be found in areas with caves, fissures, springs, and seeps (areas where groundwater come to the surface of the soil). The habitat that this species occupies is very susceptible to surface water contamination. It is not uncommon for pollutants, such as liquid manure or volatile organic compounds to permeate these areas through the small fissures. Surface contamination to groundwater can come from distance sources quite quickly during accidental spills and rainwater runoff (www.sciencebase.gov).

Development and Mitigation Considerations

The protection of groundwater resources is important for the protection of this species.

Research Needs

Little is known about the life history of the Piedmont Groundwater Amphipod. More research should be conducted to understand the phenology and reproduction of the species.



This species is commonly found in groundwater habitats such as wells, caves, seeps and springs.

Associated Ecological Communities

  • Aquatic cave community*
    The aquatic community of a subterranean stream or pond. These caves vary in their water chemistry and substrate type.
  • Spring*
    The aquatic community of very small, cold stream sources where the flow is perennial. Springs are characterized by water with constant cold temperature and are rich in dissolved oxygen.

* probable association but not confirmed.


New York State Distribution

This species is regionally endemic and has been historically known from southeastern New York. There is a large disjunction in the range between New York and Maryland.

Best Places to See

  • New York Botanical Garden Spring (Bronx County)

Identification Comments

Identifying Characteristics

The Piedmont Groundwater Amphipod is a flat shrimp-like animal with no eyes and lack of color. Males reach about 12 mm in length and females reach 9.7 mm in length. They have well developed tactile structures such as antennae and setae. Sexual dimorphism in the Piedmont Groundwater Amphipod is marked by the enlarged second antenna of the male (Holsinger 1967).

Characters Most Useful for Identification

It is very difficult to distinguish between different species of groundwater amphipods without a knowledge of the morphological characteristics of animal . Species can be distinguished by the adult body length and the characteristics of the appendages of the thoracic segments, called gnathopods. The gnathopod is a claw on the second thoracic segment of the amphipod used by males to grasp females during copulation. The tenuis group, which includes the Piedmont Groundwater Amphipod, is lacking the prominent distal notch on the palm of propodus of the first gnathopod (Fitzpatrick 1983).

Best Life Stage for Proper Identification



This crustacean feeds primarily on detritus, however there is some evidence that clay may be important to their diet (Ginet and Decu 1977).

Best Time to See

Little is known about the life history of this species, Adults are present year round (Smith 1986).

  • Present

The time of year you would expect to find Piedmont Groundwater Amphipod present in New York.

Similar Species

  • Allegheny Cave Amphipod (Stygobromus allegheniensis)
    This species is very similar to the Piedmont groundwater amphipod, however it is slightly larger. The largest males are 13.5 mm, largest females 13 mm.
  • Taconic Cave Amphipod (Stygobromus borealis)
    This species is also very similar to the Piedmont Groundwater Amphipod, however they are much smaller. The largest males are 3.0 mm and largest females 4.0 mm. In addition to size, this species is distinguished by absence of setae on palp segment 2 of mandible, reduced number of setae on inner plates of maxillae 1 and 2, unnotched spine teeth of gnathopod propods, shallow coxal plates of pereopods 3 and 4, narrow bases of pereopods 5-7, and narrow, 1-spined ramus of uropod 3 (Holsigner 1978).

Piedmont Groundwater Amphipod Images


Piedmont Groundwater Amphipod
Stygobromus tenuis (S. I. Smith, 1874)

  • Kingdom Animalia
    • Phylum Arthropoda (Mandibulates)
      • Class Malacostraca (Malacostracans)
        • Order Amphipoda (Amphipods)
          • Family Crangonyctidae (Gammarid Amphipods)

Additional Resources


Culver, D.C., J.R. Holsinger, D.J. Feller. 2012. The Fauna of Seepage Springs and Other Shallow Subterranean Habitats in the Mid-Atlantic Piedmont and Coastal Plain. Northeastern Naturalist 19 (9):1-42.

Fitzpatrick, J., 1983. How To Know The Freshwater Crustacea. Boston ...: McGraw-Hill. 143-151.

Ginet, R., and V. Decu. 1977. Initiation a` la Biologie a l'Ecologie Souterraines. J-P Delarge, Paris, France. 341pp.

Holsinger, J., 1978. Systematics Of The Subterranean Amphipod Genus Stygobromus (Crangonyctidae). City of Washington: Smithsonian Institution. Contributions to Zoology: Number 266.

Holsinger, J.R. 1967. Systematics, Speciation, and Distribution of the Subterranean Amphipod Genus Stygonectes (Gammaridae). Bulletin United States National Museum 259: 1-176.

New York Natural Heritage Program. 2024. New York Natural Heritage Program Databases. Albany, NY.

Pennak, R. W. 1975. Freshwater Invertebrates of the United States, 2nd edition.John Wiley and Sons INC.

Smith, D.J. 1984. Selected freshwater invertebrates proposed for special concern status in Massachusetts, Part II. Mass. Dept. of Env. Qual. Engineering, Div. of Wat. Pollut. Control. Westborough, MA.

www.sciencebase.gov. 2020. Statewide Assessment Of New York’S Karst Aquifers With An Inventory Of Closed-Depression And Focused-Recharge Features - Sciencebase-Catalog. [online] Available at: <https://www.sciencebase.gov/catalog/item/562a313ae4b011227bf1fe23> [Accessed 15 June 2020].

About This Guide

This guide was authored by: Lutz, Colleen M.

Information for this guide was last updated on: June 30, 2020

Please cite this page as:
New York Natural Heritage Program. 2024. Online Conservation Guide for Stygobromus tenuis. Available from: https://guides.nynhp.org/piedmont-groundwater-amphipod/. Accessed May 26, 2024.