KHODABANDEH, Saber; Univ. of Tarbiat Modarres, IRAN: The cyst envelope structure and the post-embryonic development of Artemia urmiana (Crustacea): A Light and Electron Microscopic study

Artemia is a tiny crustacean which is world-widely distributed in hypersaline media. Populations of Artemia urmiana in Urmia Lake (Iran) are among the largest biomass of bisexual artemia in the world. Investigations on reproduction have shown that A. urmiana reproduce ovoviviparously under optimal conditions and oviparously in adverse environmental conditions. The newly fertilized eggs are enclosed in three cyst envelopes: outer envelope or chorion, inner envelope and embryonic envelope. Early cleavage, gastrulation and organogenesis occur inside. The cyst diameter and chorion thickness were respectively 288.5 and 5.5 �m. The alveolar layer of the chorion was thin in comparison to other species. The hatching stage is a true nauplius with a median eye and three pairs of appendages: uniramous antennulae, biramous antennae and mandibles. During the meta-naupliar and post-meta-naupliar stages, the post-cephalic region is divided into thorax and abdomen, and eleven pairs of multifunctional thoracopods develop. Compound eyes start to develop and larval mandibles are completely reabsorbed by the end of these stages. The post-larval period is characterized by the transformation of the antennae toward their definitive form and function. During this period the compound eyes (a number of pigment cells and retinal cells) grow in size and the eyestalks develop. From a morphological point of view, A. urmiana has distinct differences from other species of artemia: the middle antennular setae possess short spines and the antennae possess eight long and one rudimentary setae. In adult A. urmiana, the total length and the lengths of different abdominal segments are longer than in other strains, whereas the furca is shorter and the number of furcal setae are less numerous in comparison to other species.