Introduction
The subphylum Crustacea was recently expanded to accommodate the Hexapoda (insects and allies) which are now considered a deep branch within the crustacean evolutionary tree. As a result of this reclassification, the Crustacea now comprises over 1 million known species. Most of the more familiar crustacean groups such as the Decapoda, Stomatopoda, Isopoda, Copepoda and Cirripedia are now included in the superclass Multicrustacea. — John W. Short, 2026
Diagnosis
Body composed of head and trunk, trunk differentiated into thorax and abdomen or comprising undifferentiated segments; if trunk undifferentiated, restricted to aquatic environments (unlike the Myriapoda); head with 3-5 pairs of free appendages including first antennae, second antennae (absent in Hexapoda), mandibles, first maxillae and second maxillae (fused to form labium in Hexapoda). — John W. Short, 2026
