Stage usually equals instar, i.e. the interval between molts. 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 1st and 2nd antennae, thoracic legs, and photophores.

Differences in the method of staging species with variability in pleopod development are illustrated in the Data Summary for Euphausia pacifica (E. pacifica Table 1 ,E. pacifica Table 2) and Nyctiphanes simplex (N. simplex Table 1), ( N. simplex Table 2).