Generally, point or period in process or development; also used morphologically.

[Crustacea] Stage usually equals instar, i.e. the interval between moults.

[Euphausiacea] In the calyptopis phase, stage number equals instar number. In the furcilia phase, a stage may be one or more instars. The definition of a furcilia stage varies among authors who describe euphausiid larval development. Some authors use the state of pleopod development and terminal telson spine number to define furcilia stages while others consider additional features including the state of first and second antennae, thoracic legs, and photophores.