triblastic
/ˈtrɪblæstɪk/Definitions
1. adjective
Relating to or characteristic of the Triblastica, a subkingdom of invertebrate animals in which the body is divided into three main parts, and the development of the embryo is not through a free-swimming larval stage.
“The triblastic worms were found to be the most diverse group of invertebrates in the area.”