The Water 3 Egg Group is mostly characterized by its members' resemblance to aquatic invertebrates; most are Water types. This group also includes several Fossil Pokémon, totaling a little more than half of those which are capable of breeding.
It is a relatively small Egg Group. Most Pokémon that are capable of breeding into other Egg Groups breed into the Water 1 Group.
Pokémon
Of the 1028 Pokémon species, 37 are in this Egg Group (3.6%).
Despite its name, this Egg Group has two evolutionary lines which are not associated with water (neither by typing nor by basis of inspiration): Skorupi and Archen.