Rhizocephala

Abstract

AbstractRhizocephalans are parasites that as adults lack any appendages, traces of segmentation, and all internal organs except for gonads and degenerated remnants of the nervous system—in fact, they bear no similarities to any arthropods. The taxonomy of the monophyletic Rhizocephala has long been recognized as artificial, taxa being diagnosed as they were largely on the basis of the gross form of the external manifestation of the parasite—that is, the female gonad bag or externa. They do have cirripede nauplii (zero to four stages) and cypris larvae. Sex is determined by size: Larger larvae become males, and smaller ones become females. As in all cirripedes, there is a lack of a functioning abdomen associated with the loss of expression of the Hox gene abdominal A.