Rhopalaea Philippi, 1843 (Diazonidae)

KOTT, PATRICIA, 2003, New syntheses and new species in the Australian Ascidiacea, Journal of Natural History 37 (13), pp. 1611-1653 : 1613

Genus Rhopalaea Philippi, 1843 (Diazonidae)

Regeneration of the thorax from epicardial tissue in the abdomen and/or posterior abdomen is a characteristic of aplousobranch ascidians, including the Diazonidae . In all families except Clavelinidae it is part of the normal replicative process and in Rhopalaea is the process by which thoraces regenerate (Salfi, 1928; Kott, 1990a; Vásquez and Young, 1996). The process does not occur in the Phlebobranchia —to which Diazonidae is erroneously assigned by Monniot (1997b) and Monniot and Monniot (2001)—in which the epicardium has an excretory function and replication is a function of the ectoderm (see Kott, 1990a).

Although regeneration occurs, colony formation has not been confirmed in Rhopalaea . Millar (1975) has described the expansion of terminal ampullae of test vessels that resembles early stages in bud formation in terminal ampullae of test vessels in the Clavelinidae . However, although Monniot and Monniot (2001) regard this as evidence of colony formation, Millar (1975: 264) emphasized that only one juvenile attached to the abdominal region of the parent had ‘organs of the zooid well differentiated’; and he did not regard it as definitive evidence of budding, referring to Salfi’s (1928) view that swelling of test vessels is not related to bud generation. Rhopalaea piru Monniot and Monniot, 1987 and R. circula Monniot and Monniot, 2001 are also reported by their authors to form colonies, the former by regeneration from the oesophageal region of the parent, and the latter by implied stolonial budding, although in neither case is the process understood.