copepods

Copepods are a group of small crustaceans in the subclass Copepoda within Crustacea. They are among the most abundant and diverse metazoans in aquatic ecosystems, occurring in nearly every freshwater and marine environment, from mountain streams to the open ocean. Most species range from about 1 to 2 millimeters in length, though some are larger.

Anatomically, copepods typically have a compact body with a distinct cephalothorax and a slender abdomen, and they bear two pairs of antennae (the paired antennules and antennae). Many possess a simple median nauplius eye. They can be free-living planktonic organisms or benthic dwellers, and their feeding modes range from herbivory on phytoplankton to detritivory and omnivory. Development follows a serial life cycle: eggs hatch into free-swimming naupliar stages (N1–N6) and then progress through copepodid stages (C1–C6) to adulthood. Reproduction is sexual; females often brood eggs in a sac or carry them on the genital somite, and males may be smaller or morphologically distinct.

Ecologically, copepods are a cornerstone of aquatic ecosystems. They graze on phytoplankton and microzooplankton and, in turn, provide essential prey for many fishes, seabirds, and marine mammals. Parasitic copepods also occur, including species that attach to fish and invertebrates. Because of their abundance and trophic position, copepods influence carbon cycling and energy transfer in oceans and freshwater systems.