Gomphonema incrassata, Mohan & Prabha, 2024

Mohan, Bala & Prabha, Duraisamy, 2024, Gomphonema incrassata sp. n., a new benthic diatom species (Bacillariophyceae: Gomphonemataceae) from Walayar Dam, Palakkad district, Kerala, India, Journal of Natural History 58 (25 - 28), pp. 775-783 : 778-780

Species Gomphonema incrassata sp. n. (Mohan and Prabha)

Dimensions: Valve length range: 30–60 µm, Valve width range: 10–15 µm, and number of striae in 10 µm: 10–14 µm. Habitat: Benthic habitat. Comments: Valves weakly heteropolar, linear-lanceolate, clavate. The head pole is bluntly round and the basal or foot pole is narrowly rounded, but they are more elongate than in Gomphonema laticollum or Gomphonema italicum . The axial area is very narrow, and the central area is small, formed by the densely spaced striae on each side that are almost indistinguishable. The frustule is club-shaped, thickened, and flexed (bent) in the girdle view. The raphe is filiform on the concave valve with well-defined proximal and distal endings, and the distal raphe is small and rounded. The striae are densely spaced at the centre, becoming parallel at the head and foot poles. Striae are radial throughout, becoming strongly radial at the apices. The single stigmata are small and round with a slit-like internal opening. Pseudospeta can clearly be seen, associated with each pole ( Figure 4 ). Holotype: Slide No. X913. Etymology: Gomphonema incrassata is named based on its frustule ornamentation, where the frustule is club-shaped, and thickened in distal endings. Gomphonema is a genus name, and incrassata is a Latin word that means ‘thickened or swollen’. Ecology: Species of the genus Gomphonema are widely found in both ultra-oligotrophic and nutrient-rich or organically polluted freshwater environments, in water of low to high electrical conductivity, and occur predominantly at neutral to slightly alkaline pH ( Yun et al. 2014). The cells are attached to the substratum by mucilage stalks at the basal pole. Record: New record.

The morphology of Gomphonema incrassata sp. n. does not match data provided for previously described taxa, but shares some features with Gomphonema laticollum Reichart. The presence of Gomphonema incrassata in just 15 samples from Walayar Dam, taken from sampling sites 3, 4 and 5, suggests that this area harbours additional biodiversity in this group, and these sampling sites receive pollutants from various sources. Hence, we can assume that the identified Gomphonema incrassata species may be widely found in nutrient-rich water bodies. Higher levels of endemism may be documented with a more thorough sampling of sites farther away from the areas of human impact. Many species of Gomphonema are considered cosmopolitan in their distribution, eg Gomphonema parvulum Kützing , Gomphonema acuminatum Ehrenberg and Gomphonema truncatum Ehrenberg ; many endemics have been described from every continent. These include Gomphonema mehleri Camburn and Gomphonema apuncto Wallace from North America; G. lepidum Fricke and G. uruguayense Metzeltin from South America; Gomphonema africanum G.S. West and Gomphonema zairense Compère from Africa; Gomphonema pinnularioides Mayer from Europe; Gomphonema ikeda Skvortzow and G. sichuanensis Li and Kociolek from Asia; G. imprime Kociolekand G. australiense Grunow ex Cleve and Möller from Australia; and Gomphonema signyensis Kociolek and Jones reported from Antarctica.

Moreover, the analysed physicochemical characteristics of the Walayar Dam water revealed that water temperature ranged from 24.76 to 25.21°C. The pH and salinity values ranged between 8.02 and 8.22, and between 1.28 and 2.61 ppt, respectively. The observed electrical conductivity, dissolved oxygen, and total dissolved solids values ranged from 295.02 to 301.82 µS cm −1, 8.05 to 9.52 mg L −1, and 622.72 to 645.55 mg L −1, respectively. Freshwater ecosystems are currently under extreme ecological stress, which may provoke certain species to decrease or become extinct ( Mohan and Priyadarshinee 2023; Mohan et al. 2023). Walayar Dam is suffering significant stress from human activities that may affect the density and diversity of the living communities in the aquatic ecosystems. According to Lu et al. (2022), diatoms are extremely sensitive to environmental changes, which reflect the variations in the physical and chemical characteristics of the water. The population density of diatoms is also influenced by the water temperature, light penetration, a high level of organic nutrients, toxic compounds, the mixing of sewage water, parasites, herbivores, and heterotrophic microbe activities ( Cavicchioli et al. 2019). Consequently, examining the water quality parameters of water ecosystems is crucial. In the present study, the analysed physicochemical characteristics such as pH, salinity, total dissolved solids, and electrical conductivity indicate that the Walayar Dam is moderately polluted. The present results underscore the need for continued research into diatom taxonomy, habitat and diversity in the least-explored geographical regions on Earth.

Figures

Figure 4. Scanning electron microscopic image of Gomphonema incrassata sp. n.