Rhizocephala, MULLER, 1862

ORDER RHIZOCEPHALA MÜLLER, 1862

Diagnosis (amended): The monophyly is assured by the molecularly based analyses of Glenner & Hebsgaard (2006) and Pérez-Losada et al. (2008). In addition, the following morphology-based apomorphies apply. All stages, including the nauplii and cyprids, lack any trace of an alimentary canal. The cyprids carry an aesthetasc seta and four additional setae on the fourth antennular segment. The male cyprids also carry a similar, but longer aesthetasc proximally on the third antennular segment. These are all parasites on Crustacea with a life cycle involving an initial and completely internal phase. This starts as a stage featuring an epitheliumenveloped bladder (primordium) containing a small lump of cells (nucleus) that represent the prospective visceral sac with the ovary. The adult parasite consists of an internal ramifying and nutrient-absorbing root system and an external sac (externa) housing the reproductive organs. All parasitic stages are without any segmentation or appendages.

Remarks: The morphological diagnosis is derived from Glenner & Høeg (1994) and Høeg & Rybakov (1992). The setation pattern of the antennules is subject to modification and loss within the order ( Høeg & Rybakov, 1996a). A detailed account of the biology and morphology is given by Høeg (1995), Høeg & Lützen (1995) and Høeg et al. (2005). Larval morphology and development are treated by Høeg (1985, 1987, 1990, 1992), Martin et al. (2014), Glenner et al. (1989, 2010) and Glenner (2001). The existing general taxonomy is treated by Høeg & Lützen (1985, 1996), Høeg & Rybakov (1992), Øksnebjerg (2000) and Høeg et al. (2019).