Stygobromus myersae

Myer's Amphipod

Family: Crangonyctidae · Class: Malacostraca · Order: Amphipoda

Conservation status: G1G2 S1S2

Myer's amphipod (Stygobromus myersae) is a freshwater crustacean in the family Crangonyctidae, a group of small, translucent amphipods adapted to subterranean aquatic environments. Like other members of the genus Stygobromus, this species likely measures 3-8 millimeters (0.1-0.3 inches) in length and exhibits the characteristic elongated, laterally compressed body form typical of amphipods. The species probably lacks pigmentation and functional eyes, adaptations common to cave-dwelling and groundwater fauna. The range and distribution of Myer's amphipod have not been comprehensively documented in available literature. Based on the Global/State Rank of G1G2 S1S2, the species appears to be extremely rare with a very limited geographic distribution, likely restricted to specific groundwater habitats or cave systems in California. The G1G2 ranking indicates the species is critically imperiled to imperiled globally, while the S1S2 ranking suggests similar rarity at the state level. Habitat requirements for this species remain poorly documented. Members of the genus Stygobromus typically inhabit groundwater environments including caves, springs, hyporheic zones, and interstitial spaces in stream gravels. These amphipods are generally associated with cool, stable water temperatures and constant moisture conditions found in subterranean aquatic systems. Specific substrate preferences, water chemistry requirements, and microhabitat needs for S. myersae have not been established through scientific study. Ecological information about Myer's amphipod is extremely limited. Like other Stygobromus species, it is presumably a detritivore, feeding on organic matter that enters groundwater systems through surface infiltration or underground streams. The species likely exhibits the slow growth rates and extended lifespans characteristic of cave-adapted fauna. Reproductive biology, seasonal activity patterns, and population dynamics remain undocumented. The conservation status of Myer's amphipod reflects significant concern about its persistence. The G1G2 S1S2 ranking indicates this species faces substantial risk of extinction, though it does not appear to be federally listed under the Endangered Species Act as of December 2025. Primary threats to groundwater amphipods typically include groundwater contamination, aquifer depletion, surface development that alters hydrology, and climate change effects on groundwater systems. The extremely limited known distribution makes the species particularly vulnerable to localized threats. Scientific documentation for this species remains limited. The information presented here synthesizes available taxonomic and conservation ranking data with general knowledge of Stygobromus ecology. Detailed studies of this species' distribution, habitat requirements, life history, and conservation needs are critically needed. We welcome contributions of verified scientific data, photographs, or field observations to enhance this species account.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.