The same process, carried further, leads to the very peculiar larva known as the Zoea, in the typical form of which, found in the Brachyura (fig.
The Zoea was formerly regarded as a recapitulation of an ancestral form, but there can be no doubt that its peculiarities are the result of secondary modification.
- Zoea of Common Shore-Crab in its second stage.
Besides the nauplius and the zoea there are many other types of Crustacean larvae, distinguished by special names, though, as their occurrence is restricted within the limits of the smaller systematic groups, they are of less general interest.
Perhaps the most striking example is the zoea-like larva of the Sergestidae, known as Elaphocaris, which has an extraordinary armature of ramified spines.
The various larval forms, especially the nauplius and zoea, were supposed to reproduce, more or less closely, the actual structure of ancestral types.
So far as the zoea was concerned, this assumption was soon shown to be erroneous, and the secondary nature of this type of larva is now generally admitted.