Note on the taxonomy of Heterosigma akashiwo (Raphidophyceae)

Abstract

Heterosigma akashiwo (Had a) Hada ex Y. Hara et Chihara is a common raphidophycean flagellate, frequently present in coastal marine waters, and occasionally causing problems in fish farming. The story of this species is a study in confusion and suppositions. Often known as Olisthodiscus luteus N. Car­ ter, it has been assigned to different classes through the years and, as demonstrated by Hara & Chihara (1987), it has ap­ parently been misidentified most of the time. Hulburt (1965) was probably the first to describe Hetero­ sigma akashiwo (as Olisthodiscus carterae Hulburt), and he was surely one of the first to compare it with Olisthodiscus luteus and recognize it as a different taxon. He also provided adequate illustrations and a Latin diagnosis as well as a de­ scription. Hada (1967) described a similar organism two years later as Entomosigma akashiwo Hada with illustrations (showing a flagellar groove) and a relevant description in English (as it was described as a protozoan). The following year he de­ scribed a new genus Heterosigma Hada (1968) and made the new combination Heterosigma akashiwo (Hada) Hada. This taxon was later given an emended description based on light and electron microscopical studies of the type culture by Hara & Chihara (1987). Based on Hulburt's (1965) description of Olisthodiscus car­ terae, Taylor (1992) made the new combination Heterosigma carte rae (Hulburt) F.J.R. Taylor, considered to be synonymous with Heterosigma akashiwo (Had a) Hada ex Y. Hara et Chi­ hara (1987), and with priority over this due to Hulburt's (1965) description predating that of Hada (1967). However, this is not the whole story, as the nomenclature rule (International Code of Botanical Nomenclature-ICBN) referred to by Taylor (1992, p. 210) states that 'the name of a new taxon of the rank of genus or below is valid only when the holotype of the name is indicated' (Art. 37.1, Greuter 1988, 1994). This condition is not fulfilled for any of the original descriptions, but Hara & Chihara (1987) designated a holotype for Heterosigma akashiwo (and provided a Latin diagnosis as they regarded it as an algal taxon), and thus this is the first name to have a valid publication.