Family DIAZONIDAE

Museums

Regional Maps

Introduction

Members of the family Diazonidae Seeliger, 1906, are characterised by their large pharynx with numerous stigmata and longitudinal branchial vessels, vertical gut loop posterior to the pharynx, oviparous habit, and gonads usually enclosed by, but sometimes behind, the gut loop.

Rhopalaea Philippi, 1843 is a solitary genus, but others form colonies with zooids either partially or completely embedded. Replication occurs by transverse division of the abdomen, and is initiated by constriction of the ectoderm in a process similar to that of most other aplousobranch families. The regenerative tissue is the endodermal epicardium. Larvae, like those of Ciona Fleming, 1822 (family Cionidae), are small and primitive with three simple, sessile, triradially arranged adhesive organs.

The family is not especially diverse, nor are its members generally recorded in particularly dense populations. Apart from two species of Rhopalaea (one of which, R. crassa, is particularly abundant in tropical waters), the genus is represented in Australian waters only by Pseudodiazona claviformis (Kott, 1963), although Syndiazona Oka occurs in the western Pacific and in due course may be found to occur in tropical waters off this continent. The Antarctic genera Tylobranchion Herdman, 1886 and Pseudodiazona Millar, 1963 have a posterior abdomen, suggesting an affinity with the family Protopolyclinidae Kott, 1990.

General References

Fleming, J. 1822. Philosophy of Zoology; or a general view of the structure, functions, and classifications of animals. Edinburgh : Hurst Vol. 2 618 pp.

Herdman, W.A. 1886. Report on the Tunicata collected during the voyage of H.M.S. Challenger during the years 1873–1876. Pt II, Ascidiae compositae. Report on the Scientific Results of the Voyage of H.M.S. Challenger 1873–1876, Zoology 14(38): 1-425

Kott, P. 1963. The ascidians of Australia IV. Aplousobranchiata Lahille; Polyclinidae Verrill (continued). Australian Journal of Marine and Freshwater Research 14(1): 70-118

Kott, P. 1990. The Australian Ascidiacea Pt 2, Aplousobranchia (1). Memoirs of the Queensland Museum 29(1): 1-266

Millar, R.H. 1963. Australian ascidians in the British Museum (Natural History). Proceedings of the Zoological Society of London 141(4): 689-746

Philippi 1843. Rhopalaea eine neues genus der einfachen Ascidien. Archiv für Anatomie und Physiologie, Leipzig 1: 45-47

Seeliger, O. 1906. Appendicularien und Ascidien, Tunicata. Manteltiere. pp. 1041-1168 in Bronn, H.G. (ed.). Klassen und Ordnungen des Tier-Reichs. Leipzig : C.F. Winter Vol. 3 Suppl.

History of changes