Zschokkella helmii n. sp. (Myxozoa: Myxosporea), a new parasite of marbled spinefoot Siganus rivulatus (Forsskal 1775), Red Sea, Egypt: light and transmission electron microscopy.

Zschokkella helmii n. sp., a new parasite of Siganus rivulatus from the Red Sea, Egypt, was described using light and transmission electron microscopy. However, the infection was severe; single "histozoic" plasmodium was encountered in the gallbladder wall. Spores are ellipsoid with 9-11 valvar striations. Spore mean length is 10.8 microm (10.0-11.0), while the spore mean width is 7.5 microm (7.0-8.0). Polar capsules are nearly round with a diameter of 2.2 microm (2.0-3.0) and have five filaments. Ultrastructure of the plasmodial wall and sporogenesis of the present species followed the usual pattern valid for most studied myxosporean species.