Post-marsupial development of Hyalella pleoacuta (Crustacea: Amphipoda): stages 1-4

The goal of this study is to describe and compare the initial stages of the post-marsupial development of Hyalella pleoacuta González, Bond-Buckup & Araujo, 2006, prior to the development of sexual dimorphism. Ovigerous females were collected in São José dos Ausentes, RS, Brazil and kept in laboratory. Juveniles were kept separately after emerging from the marsupium and were monitored daily for the presence of exuvia. Individuals from post-marsupial stages (S) 1 to 4 were dissected and illustrated. Cuticular structures were observed through SEM. Twenty three types of setae, one type of setule, two types of pores, two types of denticles and one type of penicilium were found. Cuticular structures undergo modification through development in the matters of haste size, number and size of setules, and formation of the polygonal pattern, although there is no change from one type to another. Gnathopods and antennae are the appendages that go through more modifications. The articles number of the flagellum is constant until S2. The size of the coxal plate of gnathopods in relation to the propodus has a tendency to increase throughout the stages. The uropod proportion becomes smaller in S3 when compared to S1. The number of serrate setae in the external plate of maxilla 1 varies up to S4, being different from the adult whose number is 9. The telson modifies its shape but its setae number is constant