The medusa of Thecocodium quadratum (Werner) is described and illustrated based on a specimen collected at Kuchinoerabu Island, Kagoshima Prefecture, southern Japan. This is the second collection of this species and the first record of the medusa from the sea. The present medusa is different from the holotype in having a greater number of linear spurs of nematocysts at the unbrellar margin and more distally extended, oval clusters of nematocysts on the exumbrella.
fig. 1. (iii.1993).