SEM morphological study on carapace of Cyclestheria hislopi and comparison with fossil taxa

Abstract

The circum-tropically distributed cryptic extant clam shrimp species Cyclestheria hislopi (Baird, 1859) is thought to be the only species of Cyclestherida, although molecular data show that its populations on different continents have large genetic distance (Schwentner et al., 2013). Its parthenogenetical reproduction and direct ovoviviparous development in the dorsal brood chamber indicate that C. hislopi is the sister taxon of all Cladocera (Olsen et al., 1996; Olsen, 1999; Olesen & Richter, 2013; Schwentner et al., 2018). While the large carapace, capable of enclosing the whole body, shows a close similarity with spinicaudatans. In this paper we document its carapace ornamentation by the use of a scanning electron microscope (SEM) and compare to related fossil taxa.