Australian Biological Resources Study

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Family DIAZONIDAE


Compiler and date details

P. Kott, Queensland Museum, Brisbane, Queensland, Australia

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.

 

History of changes

Note that this list may be incomplete for dates prior to September 2013.
Published As part of group Action Date Action Type Compiler(s)
14-Dec-2012 14-Dec-2012 MODIFIED
12-Feb-2010 (import)