The epizoic marine diatom Sceptronema orientale (Licmophoraceae, Licmophorales): epitypification and emendation of specific and generic descriptions 

Abstract

Sceptronema orientale was found epizoic on the harpacticoid copepod Euterpina acutifrons (Dana) collected from several locations along Bahía Anegada, Province of Buenos Aires, Argentina. Material was examined with light and scanning electron microscopy and new data about the morphology of the chloroplast and ultrastructural details of the girdle, valves, apical slit fields and rimoportulae pattern were obtained. Based on this new knowledge the descriptions of the species and of the monotypic genus Sceptronema are emended. Considering that in the protologue three pictures were designated as iconotype, the material from Ría del Jabalí is chosen as an epitype to serve as the interpretative type of Sceptronema orientale. A comparison with the morphologically similar genera Licmophora and Gato was conducted and the inclusion of Sceptronema in the Family Licmophoraceae, Order Licmophorales is proposed.

Morphology of three marine epizoic diatoms from the Mexican Pacific: Protoraphis hustedtiana, Pseudohimantidium pacificum and Sceptronema orientale (Bacillariophyta)

“…The morphological characteristics described here have been previously shown in the literature, particularly in studies using electron microscopy, and this is a confirmation of some details, such as the shape of the valves, the central (and sigmoid in two species) sternum, the fine striae and the shape of the areolae, the apical and aggregated rimoportulae (with particular orientation in Pseudohimantidium pacificum), and the slit fields at the poles (especially the species Sceptronema orientale) (e.g., Simonsen, 1970;Gibson, 1978;Rivera et al, 1986;Fernandes and Calixto-Feres, 2012;Sar and Sunesen, 2014;Gómez et al, 2020;Li et al, 2020). An exceptional morphological detail found in Pseudohimantidium pacificum is the areola, a velum of the rota type, not previously described.…”

“…The three species studied here, Protoraphis hustedtiana, Pseudohimantidium pacificum, and Sceptronema orientale, are all araphid diatoms, which usually produce mucilage pads or stalks to adhere to copepods. There are reports of large infestations of these species (Rivera et al, 1986;Fernandes and Calixto-Feres, 2012;Sar and Sunesen, 2014;Gómez et al, 2020).…”

“…The original description of Sceptronema orientale included a protocol mentioning the absence of rimoportulae in this species (Takano, 1983, p. 26), although his illustrations (figures 2 C and 17) suggest the presence of various rimoportulae. Later, Sar and Sunesen (2014) provided details of these rimoportulae in the species. The external openings of the rimoportulae were also found in this study.…”