Walcott considers Waptia as a transitional form between the Branchiopoda and the Malacostraca.
Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 172, pl. 29, figs. 7-13.
This species, though incompletely known, has several interesting characteristics. The head shows, quite plainly in some specimens, the five segments of which it is composed. The eyes are small, situated in a niche between the first and second segments, and are described as being pedunculate. The eight segments of the thorax all show short triangular pleural extensions, somewhat like those of Remopleurides or Robergia. The abdomen consists of four cylindrical segments, the last with a pair of expanded caudal rami.
The antennules appear to be short, while the antennas are large, with several segments, ending in three spines, and apparently adapted for serving as claspers in the male. The third, fourth, and fifth pairs of cephalic appendages are short, tapering, endopodite-like legs similar to those of Burgessia.
The appendages of the thorax are not well preserved, and there seem to be none on the abdomen.
This species is referred by Walcott to the Anostraca.
Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 167, pl. 27, fig. 6; pl. 28, fig. 1.
This most remarkably specialized anostracan is not well enough known to allow comparison to be made with other contemporaneous Crustacea, but it is worthy of mention.