Practice question

Crustaceans as ancestral mandibulate arthropods characteristically bear two pairs of antennae, first antennae called antennules often biramous with aesthetascs for chemoreception and second antennae frequently longer with exopod scale for swimming and mechanoreception. This dual antennal configuration doubles sensory input and enhances equilibrium via statocysts at base. Insects, myriapods and chelicerates have one pair or lack antennae entirely due to evolutionary reduction, cephalization and tagmosis. Presence of two pairs distinguishes Crustacea taxonomically from Atelocerata or Hexapoda and Chelicerata, reflected in head appendage formula used in classification keys and phylogeny.