Complex sentence: Maxillopoda is a class under the phylum Arthropoda, subphylum Crustacea, and is characterised by a reduction of the abdomen and its appendages.
Split into simpler sentences: Maxillopoda is a class under the phylum Arthropoda. It is also a class of crustaceans (subphylum Crustacea), and the class is characterised by a reduction of the abdomen and its appendages.