Stygobiont

Until recent interest in and comprehensive collection of stygofauna (Eberhard et al., 1991; Eberhard & Spate, 1995), few stygobiont amphipods were known, although there was suggestion of greater numbers than had been described (Knott, 1983, 1985; Williams, 1986).

For example, stygobiont diving beetles (Dytiscidae) breath at the water surface while stygobiont crustaceans in the same system respire within the water; so the crustaceans, but not beetles, could potentially disperse through subterranean water lacking contact with the air. Conversely, stygobiont species, typically long-lived and lacking resting stages, are dependent on the permanent presence of groundwater.

The stygobiont anthurids are only present in the tropics.

Stygobionts overwhelmingly comprise crustaceans belonging to many higher taxa, including those with broad ecological and geographical distributions (such as Copepoda, Ostracoda, Amphipoda, Isopoda, and Decapoda).

The regression model and the two-step model suggest that a marine benthic animal colonizes the marine cave, adapts to the cave environment and to the less saline water, and becomes isolated from the sea after the sea regresses, which results in a limnic stygobiont.

The new species of Alona is clearly a stygobiont, although accompanied by a fauna which is not exclusively stygobiotic.