The barnacles illustrated here are representative of two particular orders the stalked barnacles; Pedunculata (1 & 2) and the sessile barnacles; Sessilia (7 & 10). Also shown are various developmental stages including nauplier larva (3 & 8), cyprinid larva (5 & 6), intermediate forms between the two aforementioned larval stages (4 &9) and post settlement juveniles (11 & 12). Both order’s shells are comprised of carina (Ca), tergum (Te) and rostrum (R). Barnacles feed by filtering particulate matter from the water column with their jointed appendages (not labelled). Female reproductive organs, ovaries (Ov) are found near the base of the animal while the male penis (P) is associated with the testes (H) near the base of the feeding appedages. The digestive system is coloured yellow.
Examples of at least four different genera once grouped together within the order Copepoda. Now these genera diverge after the class level into too sub classes Branchiura and Copepoda as sister taxa to barnacles. Care must be taken when analysing these Subclasses relatedness as the class Maxillopoda may not be a monophyletic group.