Rhizocephala, being astomatous, cannot of course live long as Nauplii, and in the course of only a few days they become transformed into equally astomatous "pupae," as Darwin calls them.    From Wordnik.com.  [Facts and Arguments for Darwin] Reference

The Rhizocephala remain astomatous; they lose all their limbs completely, and appear as sausage-like, sack-shaped or discoidal excrescences of their host, filled with ova (Figures 59 and 60); from the point of attachment closed tubes, ramified like roots, sink into the interior of the host, twisting round its intestine, or becoming diffused among the sac-like tubes of its liver.    From Wordnik.com.  [Facts and Arguments for Darwin] Reference

Nauplius-like form, inasmuch as the plump, oval, astomatous body bears two pairs of simple rowing feet, and behind these, as traces of the third pair, two inflations furnished each with a long seta, but that beneath this Nauplius-skin a very different larva lies ready prepared, which in a few hours bursts its clumsy envelope and then makes its appearance in a form "which agrees in the segmentation of the body and in the development of the extremities with the first Cyclops-stage".    From Wordnik.com.  [Facts and Arguments for Darwin] Reference