Family CIONIDAE

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Family CIONIDAE

Compiler and date details

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

Introduction

The family Cionidae Lahille, 1887, containing a single genus, Ciona Fleming, 1822, is thought to be the most primitive of the extant ascidian families. It is characterised by solitary habit, a horizontal gut loop posterior to the branchial sac, a persistent opening into the posterior end of the pharynx from each of the pair of endodermal epicardial sacs, a large perforated pharynx (branchial sac) with internal longitudinal vessels, and numerous rows of stigmata.

The family Cionidae, once regarded as a member of the Phlebobranchia due to its large flat branchial sac and internal longitudinal vessels, was proposed as a member of the Aplousobranchia by Kott (1969). Cionids lack the renal vesicles (derived from the epicardial sac) that crowd around the gut in Phlebobranchia and Stolidobranchia (Berrill 1950). Further, the epicardial sacs remain entire as in other Aplousobranchia, and their role in the regeneration of lost or damaged tissue is homologous with their role in the replicative process of colonial Aplousobranchia. Cionids also resemble other aplousobranchs in having the gut behind the thorax (rather than alongside), the body being divided into thorax and abdomen.

This family resembles the aplousobranch family Diazonidae most closely, having a similar soft, elastic, translucent test, large branchial sac with internal longitudinal vessels, an oviparous (externally fertilised) habit, and small larvae with few larval or adult organs other than the simple triradially arranged adhesive organs. Cionidae are separated from the Diazonidae by a horizontal (rather than vertical) gut loop. Some Diazonidae form colonies, constituting a further distinction.

Cionidae are represented in Australia by a single species, Ciona intestinalis (Linnaeus, 1767). Records of C. intestinalis are from ports and harbours in all oceans, including all Australia ports, and many estuaries (Kott 1990). However, records from Australian locations later than 1983, are only from St Vincent Gulf (South Australia), Port Phillip Bay (Victoria) and Port Kembla (New South Wales).

Species of the genus Ciona have been reviewed by Hoshino & Nishikawa (1985). Detailed accounts of morphology are given by Roule (1884) and Millar (1953).