Dracunculus medinensis is a nematode that causes dracunculiasis, also known as guinea worm disease. The disease is caused by the female which, at around 80 centimetres in length, is among the longest nematodes infecting humans. In contrast, the longest recorded male Guinea worm is only 4 cm.

Copepods are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic, some are benthic, a number of species have parasitic phases, and some continental species may live in limnoterrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds, puddles, damp moss, or water-filled recesses of plants (phytotelmata) such as bromeliads and pitcher plants. Many live underground in marine and freshwater caves, sinkholes, or stream beds. Copepods are sometimes used as biodiversity indicators.