I have just checked with my copy of RIEDL, 1983 and find the description and picture of the medusa of Zanclea costata (= Z. implexa) quite matching the one you have photographed here. So tentatively this or a closely related other genus/species within the Zancleidae would be my suggestion.
But please note that my knowledge of marine cnidaria is rather limited, so take this 'cum grano salis', yet possibly a helpful starting point for your further search.