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Gomphosphenia biwaensis, a new diatom from Lake Biwa, Japan: description and morphometric comparison with similar species using an arc-constitutive model

A new diatom species Gomphosphenia biwaensis Ohtsuka & D.Nakai was described from the south basin of Lake Biwa in Central Japan. Scanning electron microscopy revealed that the fine structure of this species is typical of the genus Gomphosphenia, although the striae are composed of a few areolae unlike Gomphosphenia lingulatiformis, the type species of the genus. Based on light micrographs of more than 100 specimens, the radii of the head pole, foot pole, and each valve side of these specimens were measured within a range that can be approximated by an arc, as well as the valve length, width, and stria density. The morphometric data were log-transformed and orthogonalized using principal component analysis based on the correlation coefficient, and the first principal component was eliminated to remove the effect of size differences. The second and subsequent principal components approximately followed a multivariate normal distribution. Morphometric data of the specimens from the other samples from Lake Biwa and its satellite lakes mostly fell into the 99% confident ellipsoidal cylinder, whereas those of the other Gomphosphenia species, whose striae are composed of multiple areolae, were all excluded from it. We therefore concluded that G. biwaensis is a new species of Gomphosphenia. It was an abundant epiphyte on Lyngbya wollei, a benthic filamentous cyanobacterium, which flourishes in Lake Biwa's south basin. However, L. wollei seems to not be the original host because it is probably an exotic species to Lake Biwa that has rapidly increased since 2012, while G. biwaensis was also present in samples collected there in 2000.