Maxillopoda is a diverse class of crustaceans including barnacles, copepods and a number of related animals. It does not appear to be a monophyletic group, and no single character unites all the members.

Maxillopoda. Retrieved May, 08 2021, from en.wikipedia.org/wiki/Maxillopoda.

Sessilia is an order of barnacles, comprising the barnacles without stalks, or acorn barnacles. They form a monophyletic group and are probably derived from stalked barnacles. The order is divided into three suborders. The Brachylepadomorpha contain a single family, Neobrachylepadidae, while the Verrucomorpha contain two families, Verrucidae and Neoverrucidae. The remaining 12 families are in the suborder Balanomorpha.

Sessilia. Retrieved May, 08 2021, from en.wikipedia.org/wiki/Sessilia.

The Balanidae comprise a family of barnacles of the order Sessilia, containing these genera:

Balanidae. Retrieved May, 08 2021, from en.wikipedia.org/wiki/Balanidae.