Polysyncraton (Ascidiacea, Didemnidae): a re-examination of some specimens and descriptions of three new species

Polysyncraton Nott, 1892 is the second largest genus of didemnid ascidians; it has a wide distribution ranging from temperate to tropical waters. Seventy-one specimens of Polysyncraton from eight museum collections and recently collected samples were analyzed. This resulted in the description of three new species (P. cabofriense Oliveira & Rocha sp. nov. from Brazil, P. globosum Oliveira & Rocha sp. nov. from Australia and P. snelliusi Oliveira & Rocha sp. nov. from Suriname) and emended descriptions of three further species (P. amethysteum (Van Name, 1902), P. magnilarvum (Millar, 1962) and P. purou C. Monniot & F. Monniot, 1987).

Pattern of stigma numbers as a taxonomic character in some didemnid ascidians (Aplousobranchia: Didemnidae)

Colonial animals are often lacking in taxonomic characters due to their small size and the simple morphology of zooids. Since zooid size is nearly uniform in many colonial ascidians, the stigma numbers in each row can be a useful taxonomic character. To evaluate their potential utility, we investigated intraspecific variations in stigma patterns in a subset of photosymbiotic didemnid ascidians, including five morphotypes of Didemnum molle, Lissoclinum midui, Trididemnum clinides, and T. nubilum. Stigma number patterns were almost stable in L. midui and T. nubilum. In contrast, there was considerable variation in stigma number even among clone zooids within the same colony in D. molle and T. clinides. Further, the stigma patterns did not differentiate the five morphotypes of D. molle. There was no significant correlation between the total number of stigma and the length of the thorax in any of the species examined here, suggesting that stigma number is probably invariable within each zooid. Stigma patterns can be usable as a taxonomic character in didemnid ascidians, particularly in species having one or a few patterns. Even in species with various patterns, the range of variation will be informative once such ranges are comprehensively described for didemnid species.

Taxonomic significance of tunic spicules in photosymbiotic ascidians: a quantitative and molecular evaluation

Many didemnid ascidians have calcareous spicules in the tunic. Since the spicules of each species have a specific shape and size-range, they are often regarded as an important character for taxonomy. To evaluate the taxonomic significance of tunic spicules, a quantitative survey of spicule size and shape was combined with a molecular phylogeny inferred from the partial sequence of the cytochrome c oxidase subunit I (COI) gene in some groups of didemnid species that are supposedly closely related. This study revealed the presence of substantial intraspecific variations in the shape and size of tunic spicules. The spicules are, therefore, not always crucial features discriminating species, particularly among related species. Although tunic spicules are potentially valuable features for didemnid taxonomy, their intraspecific variation should be carefully considered before they are used as a key character for species identification.