In the Decapoda the branchial system is more complex.
It is among the Malacostraca, however, and especially in the Decapoda, that the " gastric mill " reaches its greatest perfection.
In the Decapoda the antennal gland is largely developed and is known as the " green gland."
In the Decapoda three pairs are thus modified, and in the Tanaidacea, Isopoda and Amphipoda only one.
A minute entosternite having the above-described structure is found in the Crustacean Apus between the bases of the mandibles, and also in the Decapoda in a similar position, but in no Crustacean does it attain to any size or importance.