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Epipsammic diatom Planothidium pseudolinkei unlocks potential for intertidal zone chromista diversity

NEWS - Researchers describe a new species of monoraphid diatom, Planothidium pseudolinkei, from the coast of Guangxi using light and scanning electron microscopy. This species is distinguished from other species by the morphological features of capitate apices, multiseriate striae, small central areas on raphe valves, and oval sinuses on valves without raphes.

Epipsammic diatom Planothidium pseudolinkei unlocks potential for intertidal zone Chromista diversity

Planothidium is a species-rich genus and is widely distributed in freshwater, brackish and marine environments. Most are found in freshwater habitats and only a few taxa are marine or brackish species, but the species diversity in marine environments is thought to be higher than previously reported.

Several recently discovered marine Planothidium species such as P. galaicum, P. juandenovense and P. kaetherobertianum have symmetrical central areas, but the density of striae is often not useful for distinguishing species with similar cavities or sinuses.

Researchers from Guangxi Academy of Sciences in Nanning, Guangxi University in Nanning and the Chinese Academy of Sciences in Qingdao found that P. pseudolinkei has a unique combination of morphological features of capitate apex, multiseriate striae, thickened virgae and an internal depression in the central area of the rapheless valve that separates it from all other species.

The new species is easily confused with P. linkei because both have similar valve lines, overlapping valve dimensions, similar striae density, unilateral central area of the rapheless valve and both are in marine habitats. The specific epithet, pseudolinkei, refers to the morphological and habitat similarities with P. linkei.

Planothidium is a typical benthic diatom genus with diverse ecological preferences. They can attach to a variety of inorganic and biotic substrates via the raphe valve. P. delicatulum and P. deperditum are epipsammic diatoms, P. galaicum and P. hinzianum are epiphytic diatoms, and P. africanum is an epilithic diatom.

Interestingly, P. kaetherobertianum is an epizoic species that resides on the carapace of sea turtles. P. pseudolinkei is an epipsammic diatom collected from the tidal zone in Fangchenggang City. Epipsammic diatoms adapt to sandy environments with unstable substrates and insufficient nutrients.

Previous studies have described the biodiversity of diatoms in this specific habitat and improved the understanding of marine epipsammic diatoms. The researchers speculate that more epipsammic taxa will be discovered as further investigations of sand samples from various coastal areas in China continue.

Original research

Li L, Huang Y-Y, Nong Q-Z, Lai J-X, Li Y-H (2024). Planothidium pseudolinkei sp. nov. (Bacillariophyta), a new marine monoraphid diatom species from the coast of Guangxi, China. PhytoKeys 246: 237-249, DOI:10.3897/phytokeys.246.128068
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