The first larval stage (instar I; 400 to 500 μm in length) has a brownish-orange colour, a red
nauplius eye in the head region and three pairs of appendages: i.e. the first antennae
(sensorial function), the second antennae (locomotory + filter-feeding function) and the
mandibles (food uptake function). The ventral side is covered by a large labrum (food uptake:
transfer of particles from the filtering setae into the mouth). The instar I larva does not take
up food as its digestive system is not functional yet; it thrives completely on its yolk reserves.
After about 8 h the animal molts into the 2nd larval stage (instar II). Small food particles (e.g.
algal cells, bacteria, detritus) ranging in size from 1 to 50 μm are filtered out by the 2nd
antennae and ingested into the functional digestive tract.
The larva grows and differentiates through about 15 molts. Paired lobular appendages are
appearing in the trunk region and differentiate into thoracopods (Fig. 4.1.4.). On both sides of
the nauplius lateral complex eyes are developing (Fig. 4.1.5.and 4.1.6.). From the 10th instar
stage on, important morphological as well as functional changes are taking place: i.e. the
antennae have lost their locomotory function and undergo sexual differentiation. In males
(Fig. 4.1.6. and 4.1.8.) they develop into hooked graspers, while the female antennae
degenerate into sensorial appendages (Fig. 4.1.11.). The thoracopods are now differentiated
into three functional parts (Fig. 4.1.13.), namely the telopodites and endopodites (locomotory
and filter-feeding), and the membranous exopodites (gills).