Calothrix sp.
[C. Agardh 1824] Bornet et Flahault 1886 (John et al. ed. 2002)
Family: Trichome (filamentous structure) tapered from base to tail
Genus: Heterocysts present; one trichome within a sheath; coenobium absent
(Illustrations of The Japanese Fresh-water Algae, 1977).