Family RITTERELLIDAE

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Introduction

Genera in the family Ritterellidae Kott, 1992 have 6-lobed, separately opening apertures, a short abdomen, a stomach with a longitudinally folded wall halfway down the descending limb of the gut loop and a long narrow posterior abdomen containing serially arranged gonads. Parastigmatic vessels sometimes cross each row of stigmata and sometimes papillae (possible vestiges of internal longitudinal vessels as in Protopolyclinidae) are on the transverse branchial vessels. Sand often is crowded in the test making it hard and brittle. Zooids always are embedded, often in long, narrow sandy branches in which each terminal branch has zooids arranged in a system with the atrial apertures on one side and branchial apertures in an arc on the other side. These are not true cloacal systems, although in some species zooids are arranged in circles in rudimentary cloacal systems (as in some Polycitoridae). Larvae are incubated in the atrial cavity, where the eggs may be fertilised. Most larvae resemble those of Polyclinum Savigny, 1816, with paired dorsal and postero-ventral strands of epidermal vesicles. Only Ritterella dispar Kott, 1957 has vesicles between the adhesive organs as in Aplidium Savigny, 1816.

Zooids are distinguished from those of Protopolyclinidae and Euherdmaniidae by their long posterior abdomen with serially arranged gonads. Pseudodistomidae have wider thoraces with only three rows of stigmata. The zooids are similar to those of Aplidium species, with the gut loop short, stomach folded, and posterior abdomen very long. They possibly share a common ancestor with Aplidium and may have evolved from Protopolyclinidae in parallel with Polyclinum and other genera of the Polyclinidae. The two known genera, Ritterella Harant, 1931 and Dumus Brewin, 1952 formerly were included in the Euherdmaniinae Ritter, 1903, a subfamily of the Polyclinidae, together with other genera characterised by their separately opening atrial apertures.

A few tropical species are known, but Ritterellidae are mainly temperate, in the western Pacific both north and south of the tropics, and in the eastern Pacific north of the equator. In the Atlantic Ocean only one specimen of a newly described species (R. glareosa Monniot, 1974) is reported from an isolated sea-mount off the Azores. The type species of the monotypic genus Dumus is one of the few known trans-Tasman species. Ritterella is well represented in southern Australian waters.

General References

Brewin, B.I. 1952. Ascidians of New Zealand, Part 7 Ascidians from Otago coastal waters, Part 2. Transactions of the Royal Society of New Zealand 79(3/4): 452-458

Harant, H. 1931. Contributions à l'histoire naturelle des ascidies et de leurs parasites. Annales de l'Institut Océanographie, Monaco & Paris 8(4): 229-389

Kott, P. 1957. The sessile Tunicata. Scientific Reports of the John Murray Expedition 10(4): 129-149

Kott, P. 1992. The Australian Ascidiacea Pt 3, Aplousobranchia (2). Memoirs of the Queensland Museum 32(2): 377-620

Monniot, F. 1974. Ascidies littorales et bathyales récoltés au cours de la campagne Biaçores: Aplousobranches. Bulletin du Muséum National d'Histoire Naturelle, Paris [published 1907-1971] 3 173(226): 1287-1325

Ritter, W.E. 1903. The structure and affinities of Herdmania claviformis, the type of a new genus and family of ascidians from the coast of California. pp. 237–261, pls xviii, xix. in, Mark Anniversary Volume. New York : Henry Holt & Co.

Savigny, J.C. 1816. Recherches anatomiques sur les ascidies composées et sur les ascidies simples—Système de la classe des Ascidies pp. 1–239. In Mémoires sur les Animaux sans Vertèbres, Pt 2. Paris : G. Dufour.

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