Dark field light micrograph of the water flea, Simocephalus vetulus. The long second antenna on the ventral side is used to move Simocephalus through the water. The digestive track, located on the dorsal side is darkly pigmented due to the presence of food and this female's eggs appear green. Simocephalus are filter feeders that ingest any algae, protozoan, or organic detritus of the right size.