Family PYCNOCLAVELLIDAE

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Introduction

The family Pycnoclavellidae Kott, 1990 has characters that to some extent resemble those of Clavelinidae, having smooth apertures and usually only partially embedded zooids. Pycnoclavellid zooids have small thoraces and a relatively long narrow stalk, containing an invariably long gut loop with the stomach at its posterior end. A vascular stolon extends from the posterior end of the zooid. The compact gonads are in the distal end of the gut loop. Larvae are relatively large, and have two or three tubular adhesive organs invaginated into the larval haemocoele from the anterior end of the larval trunk. To effect settlement, these evert as long cylindrical, anterior projections with terminal adhesive cells. The eggs, fertilised at the base of the oviduct, form a developmental series as they move up towards the atrial cavity.

Pycnoclavellid species were formerly included in the family Clavelinidae owing to the smooth-rimmed apertures and the presence of a vascular stolon. Family status was proposed by Kott (1990) on the basis of its differences from Clavelinidae, namely, its very long gut loop, distinctive larval adhesive organs, relatively small gonads, and replication by horizontal division of the abdomen involving the epicardium (Trason 1963). Euherdmania (Euherdmaniidae) has similar adhesive organs and fertilisation at the base of the oviduct and a long gut loop. However, its gonads usually are behind the gut loop, and it has lobed apertures. In defining this family, Kott (1990) included fertilisation at the base of the oviduct as a character distinguishing it from Clavelinidae. However, species in the Detorta group of the genus Pycnoclavella are an exception, fertilisation occurring in the atrial cavity at the top of the thorax (see Kott 2005).

Two genera are known. The monotypic Euclavella Kott, 1990 has a temperate range from New Zealand to eastern Australia, and Pycnoclavella Garstang, 1891 is well represented in Australian waters by two tropical and four temperate species, all brightly coloured and forming large clusters of partially embedded zooids with characteristic small, inflated thoraces and long, narrow gut loops.

General References

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

Kott, P. 2005. Pycnoclavella (Ascidiacea, Tunicata) from the Western Indian Ocean. African Zoology 40(2): 10 pp.

Trason, W.B. 1963. The life cycle and affinities of the colonial ascidian Pycnoclavella stanleyi. University of California Publications in Zoology 65(4): 283-326

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