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 three pairs are thus modified, and in the Tanaidacea, Isopoda and Amphipoda only one.
In the Decapoda the antennal gland is largely developed and is known as the " green gland."
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.