Bathycoelia thalassina[1] is a species of African shield bugs in the subfamily Pentatominae.

B. thalassina is a large, mostly green species of shield bug with a length of 20–21 mm.

The pronotum has very dense puncturing, the surface of the disk therefore rugose and opaque.

[2] B. thalassina has been recognised as a 'new encounter pest' of West African cacao, Theobroma cacao since the 1960s, when it was observed that "large nymphs and adults … feed on developing cocoa pods, causing damage to the beans.

The adults have long feeding stylets (about 22 mm) which can penetrate the pod cortex and suck liquid from the developing beans.