Larval forms in crustaceans

larval forms in crustacens

1. LARVAL FORMS OF CRUSTEANS

2. NAUPLIUS Nauplius is the first and the fundamental larva of most of crustaceans. It is minite,free swimming,pelagic larva. It’s body is oval and unsegmented,with a median dorsal eye and three pairs of unjointed lateral appendages ,namely antennular,antennary and mandibular appendages

3. Antennular appendages are uniramous, and the others are biramous Anus is located at the posterior tip Nauplius undergoes repeated moults and, in most crustaceans, transforms to the metanauplius stage

4. Metanauplius Metanauplius represent an advanced stage of nauplius It’s body is elongated, with an oval cephalo-thoracic region and a terminally forked abdomen Anteriorly, cephalo-thoracic has a pair of papilliform frontal organs

5. Ventro laterally, there are the paired antennular,antennary and mandibular appendages and the rudiments of four pairs of appendages

6. Protozoea Protozoea has an enlarged and elongated body, differentiated into cephalo-thorax and abdomen Cephalo-thorax is covered by the carapace or dorsal shield

7. Zoea Zoea is truly an advanced protozoea It is the second important crustacean larva In zoea, the cephalothorax becomes much developed and the abdomen becomes six segmented

8. The median eye of the protozoea disappears, but the compound eyes become stalked and movable

9. ALIMA In squilla, the embryo hatches out from the egg as a modified zoea known as kalima larva It is glassy and transparent pelagic larva, with clean body covered by short and broad carapace

10. Carapace bears a rostrum Body has three divisions head,thorax and abdomen Head bears the antennules,antennae and the stalked compound eyes

11. Music or schizopod Mysis is found in the life cycle of Pegasus
It’s body is long and lean with an elongated and six segmented abdomen Abdomen appendages make their appearance and develop to biramous pleopods swimming legs The last pair of swimmerets eventually transform to uropods

12. Megalopa Cephalothorax is large and crab like,with well developed appendages, large and stalked compound eyes and a carapace produced into a rostrum Abdomen is six segmented with functional pleopods