ALGAL SYMBIONTS IN THE TUNICS OF 6 NEW-ZEALAND ASCIDIANS (CHORDATA, ASCIDIACEA)

Filamentous eukaryotic algae were found completely embedded in the tun ic matrix of 6 species of ascidians from the cold-temperate waters of southern New Zealand: the aplousobranch Aplidium thomsoni (Polyclinida e) and 5 solitary stolidobranchs, Asterocarpa humilis (Styelidae) and Pyura cancellata, P. carnea, P. pulla, and P. suteri (Pyuridae). All t he ascidians appeared to be completely healthy, and the stolidobranchs showed evidence of tunic blood vessel hypertrophy in the regions of a lgal filaments. Only those individuals growing in at least a low-light environment contained algae; individuals of the same species growing in dark conditions contained none. The algal symbionts include Neevea repens (Rhodophyta), Pseud endoclonium submarinum and Ostreobium queke ttii (Chlorophyta), and an unidentified filamentous (probable) phaeoph yte. Dense growths of Neevea and Pseudendoclonium were found in the tu nic matrix in all six ascidians, most abundantly just under the tunic cuticle but extending several millimeters into the tunic. Subsequent r ecent discovery of filamentous chlorophytes in the tunic of two specie s of American Pacific coast solitary ascidians leads us to conclude th at this algal habitat may be a widespread phenomenon that has been ove rlooked in the supposition that the algae were merely epizoic. Most of these ascidians also contained numerous alga-filled tunic pockets pro bably formed during the incorporation of sand grains with epipsammic a lgae that later proliferated. Though previously noted anecdotally in t he literature, this report is the first compilation of this algal asse mblage. They include Sarcinochrysis marina (Chrysophyta), unidentified diatoms, unicellular chlorophytes, and the prokaryote cyanobacteria D ermocarpa, Xenococcus, and Synechococcus. Similar species, along with Oscillatoria, Spirulina, and Anabaena, were also found in the inter-tu nic cavity of the peculiar double-tunic ascidians Pyura cancellata and P. carnea.