PYURIDAE, Hartmeyer, 1908

Mead, A., Carlton, J. T., Griffiths, C. L. & Rius, M., 2011, Introduced and cryptogenic marine and estuarine species of South Africa, Journal of Natural History 45 (39 - 40), pp. 2463-2524 : 2507

Family PYURIDAE

Microcosmus squamiger Michaelsen, 1927 Introduced

A highly successful fouling solitary ascidian that forms dense monospecific clumps within its introduced range ( Rius et al. 2009a). The tunic is generally covered by mud and epibionts, which makes its identification in the field difficult. As many studies have wrongly identified Microcosmus squamiger as Microcosmus exasperatus ( Turon et al. 2007) a careful observation of the shape of the siphonal spines is required to differentiate these closely related species ( Monniot et al. 2001). Both taxonomic ( Michaelsen 1927; Kott 1985; Monniot et al. 2001) and genetic ( Rius et al. 2008) studies indicate that the origin of Microcosmus squamiger is Australia. This species has a worldwide distribution, including Australia, Europe, California, India and South Africa ( Rius et al. 2008). Millar (1955, 1962) reported Microcosmus exasperatus from Durban samples collected in 1950 and 1952 (east coast). However, the description was so poor that the specimens described could be attributed to either Microcosmus exasperatus or Microcosmus squamiger . As no Microcosmus exasperatus have been found in recent surveys ( Monniot et al. 2001; M. Rius, unpublished results), we assume that the specimens collected by Millar were Microcosmus squamiger so we take the first collection of this species in South Africa as 1950. The reports of Microcosmus squamiger in Alexander Bay and Table Bay by Griffiths et al. (2009) and again by Haupt et al. (2010a) were misidentifications of another introduced ascidian, Cnemidocarpa humilis . Besides the fact of being a harbour species, Microcosmus squamiger has been found in open coast locations within its introduced range. In the Mediterranean Sea, it can cover all available substrata, achieving densities of up to 2300 individuals / m 2 and displacing native communities ( Rius et al. 2009a).