The sub-class Arachnida are at once recognized by their eight legs.
A Monograph of the sub-class Cirripedia, with figures of all the species.
The first sub-class consists of the Hags (Hyperotreta, or Myxinoida).
The Hydromedusae represent, therefore, a sub-class of the Hydrozoa.
Each 'phratry' then bartered a sub-class of its own for a sub-class of its partner.
At this ...