Class APPENDICULARIA

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Class APPENDICULARIA

Compiler and date details

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

Introduction

Appendicularians are small free swimming planktonic tunicates, their bodies consisting of a short trunk and a tail (containing the notochord cells) which is present through the life of the individual. Glandular (oikoplast) epithelium on the trunk secretes the mucous house which encloses the whole or part of the body and contains the complex filters which strain food from the water driven through them (Deibel 1998; Flood & Deibel 1998). Unlike other tunicates, there is no peribranchial cavity and a pair of pharyngeal perforations (spiracles) surrounded by a ring of cilia open directly to the exterior from the floor of the pharynx.

The early studies of these organisms, begun with Chamisso's description of Appendicularia flagellum Chamisso, 1821, were confounded by questions of its phylogenetic affinity. Chamisso classified his species with medusoids, Mertens (1830) with molluscs, and Quoy & Gaimard (1833) with zoophytes. Only in 1851 were appendicularians correctly assigned to the Tunicata by Huxley. At the time of this placement, the existence of more than one taxon was only just beginning to be recognised, and despite Huxley's work, they were not universally regarded as adult organisms—some authors still insisting that they were ascidian larvae or a free swimming generation of the sessile ascidians (Fenaux 1993). Subsequently, these questions were resolved by the work of Fol (1872) on material from the Straits of Messina, which forms the basis of later studies on the large collections of the great expeditions of the 19th century that revealed their true diversity in the oceanic plankton.

Appendiculariadae Brown, 1862 (at family level) and Appendicularia (as a tribe) were the first collective names given to this group of organisms. Fol (1872) applied the family name Appendiculaires to the group. Appendicularia predates Copelata Haeckel, 1866, Larvacea Herdman, 1882 and other names at ordinal or class level (see Fenaux 1993). It is, accordingly, the name given to the class in the present work.

Lohmann (1892–1931) and Lohmann & Bückmann (1926) made important contributions to the study of the group, as did Aida (1907–1908) and Tokioka (1940 et seq.) in Japanese waters, and Ritter (1905) and Essenberg (1926) off California. Fenaux et al. (1990) published a bibliography and Fenaux (1993) completely revised the group and reviewed its history. The taxonomy and biology are reviewed in Bone (1998).

The classification within the class is generally that originally proposed by Lohmann (1896a) and followed, with minor modifications, by later workers. The families are Oikopleuridae Lohmann, 1896a, Fritillariidae Seeliger, 1895 and Kowalevskiidae Lahille, 1888. They are distinguished from one another by characteristics of body shape, endostyle, pharyngeal perforations, stomach wall, oikoplast epithelium and tail.

In Australia, the appendicularians of the eastern coast collected by the CSIRO research vessel FRV Warreen between the Tropic of Capricorn and South Australia were studied and recorded by Thompson (1945). A few species were recorded from Shark Bay and off Fremantle by Lohmann (1909), but there is no systematic study on this group in western Australian waters or in the tropical or the southern coastal waters of the Australian continent. So far, no indigenous species are known.

As with the thaliaceans, the geographic ranges of most species are great, being defined by the course of the relevant ocean currents rather than by geographic regions. Tokioka (1960) reviewed the geographic distribution of species in the class.

The search for the location of type specimens of the class has been unsuccessful. In particular, the collections of the Humboldt Plankton Expedition (Lohmann) and the Deutsch Tiefsee Expedition (Lohmann 1892–1931) have not been found. At this stage, no relevant larvacean type specimens have been located in the Natural History Museum (London), U.S. National Museum of Natural History (Washington, D.C.), the American Museum of Natural History (New York), the Muséum d'Histoire Naturelle, (Geneva), the Natural History Museum (Vienna), the Muséum National d'Histoire Naturelle (Paris), the Naturhistoriske Riksmuseum (Stockholm), Museum für Natuurkunde (Berlin) or the Japanese collections. Hopefully, the publication of this section of the Catalogue will advertise the need for information on the location of the type specimens in this taxon of the Tunicata, although it is probable that many were lost during World War II (Fenaux 1993).