Bio agent test droids were droids which had insectile heads atop torsos similar to those of B2 super battle droids.
It seems to have been designed as a specialized science droid for use in combat zones, with enhanced sensor equipment. It had a large, broad head, with its front mostly taken up by a pair of bright orange photoreceptors and a cluster of aerials on top, further augmented by two sensor arrays rising behind from the back of the shoulders. It also boasted more dexterous hands than standard super battle droids, with three long, slender fingers and an opposable thumb, and its twin blasters were mounted on the right shoulder rather than the wrist.
The Separatists deployed these droids in the testing of swamp gas on Ohma-D'un. They were analyzing the results of the attack on the Gungan colony when they were encountered and destroyed by Obi-Wan Kenobi and his team.