History of the larval forms[186].
The larval forms of the Crustacea appear to have more faithfully preserved their primitive characters than those of almost any other group.
Branchiopoda.
The Branchiopoda, comprising under that term the Phyllopoda and Cladocera, contain the Crustacea with the maximum number of segments and the least differentiation of the separate appendages. This and other considerations render it probable that they are to be regarded as the most central group of the Crustaceans, and as in many respects least modified from the ancestral type from which all the groups have originated.
The free larval stages when such exist commence with a larval form known as the Nauplius.
The term Nauplius was applied by O. F. Müller to certain larval forms of the Copepoda ([fig. 229]) in the belief that they were adult.
Fig. 208. Two stages in the development of Apus cancriformis.
(After Claus.)
A. Nauplius stage at the time of hatching.
B. Stage after first ecdysis.