The San Diego fairy shrimp is a small aquatic crustacean in the order Anostraca. It was listed as endangered in 1997, and threats to the species include indirect impacts of development, off-highway vehicles, non-native plants, hybridization and competition, disease and altered hydrology.
Male San Diego fairy shrimp are distinguished from other Branchinecta species males by differences in the distal tip, meaning that it is located far from the point of attachment, of the second antennae. Females are distinguishable from other Branchinecta species females by the shape and length of the brood sac, length of the ovary and presence of paired dorsolateral, meaning located on the sides, toward the back, spines on five of the abdominal segments.
They are generally restricted to vernal pools and other non-vegetated ephemeral basins that are between 2 and 12 inches in depth.
San Diego fairy shrimp are usually observed from January to March when seasonal rainfall fills vernal pools and initiates egg hatching.
They feed on algae, diatoms and particulate organic matter.
Individuals hatch and mature within 7 to 14 days of rainfall filling a pool, depending on water temperature. Cysts produced from successful reproduction are either dropped to the pool bottom or remain in the brood sac until the female dies and sinks. Cysts are capable of withstanding temperature extremes and prolonged drying.
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