Crustacean Larvae Crustaceans show both direct and indirect

Crustacean Larvae Ø Crustaceans show both direct and indirect development. Ø Many of the Crustaceans undergoes indirect development. Ø Involving wide varieties of larval forms, of these 3 main are Nauplius, Zoea and Megalopa. üNauplius Larva § Nauplius larva is the characteristic of class Crustacea. § It is the simplest type of larva, found in most marine crustaceans. § The body of Nauplius is minute with 3 indistinct regions, a single median eye and 3 pairs of appendages

• The uniramous antennules, mainly the balancing organ; biramous antennae, principal locomotor organ and mandibles, alongwith antennae share for food collection. • In the branchiopods the nauplius develops directly into adult. • But in other crustaceans it may gives rise to several larval forms (metanauplius, protozoea, mysis etc. ).

Zoea Larva § In almost all decapods, except few, hatching takes place at zoea stage like true crabs. § It has a broad cephalothorax, Curved abdomen with forked telson. § Helmet like carapace has 2 long spines, a median dorsal & median rostrum. § Two lateral spines are always fused. § a pair of compound eye present. § Rudimentary thoracic appendages are present § Biramous maxillipedes present, used for swimming.

Megalopa Larva • In brachyuran decapods (crabs) Zoea stage metamorphoses in to megalopa. • It resembles to some extent with adult crab • In crabs nauplius stage is passes within egg which hatches as zoea. • By moulting megalopa metamorphosed to adult. • Megalopa have larger eyes than adults, carapace is narrower and smoother. • In megalopa the abdomen projects posteriorly even when it is tucked under thorax in adults.

LARVAL FORMS OF CRUSTACIA

Significance of Larval Crustacean Larvae • Every organism during development (ontogeny), repeats to some extent its evolutionary history (phylogeny). • The nauplius was regarded to be representing ancestral for a crustacea. • It was presumed that from ancestral form, the present day crustaceans evolved phylogenetically. • The larval stages are useful for finding out affinities & connecting links among various groups.