Paralarvae is the term used to describe the young plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

ic stages of cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s, between hatchling and subadult. It is used to differentiate it from the term 'larva' used in animals which undergo true metamorphosis

Metamorphosis

Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...

. They have been observed only on members of the orders Octopoda and Teuthida.

The term was first introduced by Richard E. Young and Robert F. Harman in 1988.