Aspects of this topic are discussed in the following places at Britannica.
...Anomopoda. The foregut shows the greatest range of structure; in some crustacean species it is a simple tube, but in decapods it reaches great complexity in forming a chitinized structure called the gastric mill. This consists of a series of calcified plates, or ossicles, that are moved against each other by powerful muscles, making an efficient grinding apparatus. The junction between the mill...
in malacostracan: Digestion and nutrition )...part of the thorax. Lining the inside of the greatly folded and muscular stomach walls, especially the pyloric portion, are groups or rows of stiff bristles, teeth, and filtering setae known as the gastric mill. The mill is strongly and complexly developed in large decapods, which ingest food quickly and in coarse chunks. The filtering setae are prominent in malacostracans that ingest fine...
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