Copepod and Water flea

Copepod noun - Minute marine or freshwater crustaceans usually having six pairs of limbs on the thorax; some abundant in plankton and others parasitic on fish.

Water flea and copepod are semantically related. In some cases you can replace phrase "Water flea" with "Copepod", this terms are similar.

Water flea noun - Minute free-swimming freshwater copepod having a large median eye and pear-shaped body and long antennae used in swimming; important in some food chains and as intermediate hosts of parasitic worms that affect man e.g. Guinea worms.

Copepod and water flea are semantically related. You can use "Copepod" instead a noun phrase "Water flea".