Copepod and algae. Polarised light micrograph of a nauplius larva (left), with Dinobryon sp. golden algae (chrysophytes, centre) and a Cosmarium sp. desmid green alga (right). A nauplius is the first larval stage of a copepod crustacean in which the thorax and abdomen have not developed yet. Nauplii larvae do not feed, but use internal yolk reserves from the egg for energy. Desmids are a common group of freshwater single-celled algae that have intricate cell walls. Magnification: x100 when printed 10 centimetres wide.