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Description
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Chamaepinnularia mirim M.G.Junqueira, L.O.Crossetti & C.E.Wetzel, sp. nov. (Figs 1–11 LM, 12–16 SEM). Light microscopy (LM) (Figs 1–11): ―Valves lanceolate to linear-lanceolate with an inflated central area and markedly capitate, broadly rounded apices (Figs 1–11). Valves with broadly protracted apices and expanded central area. Valve length 4.68–7.93 μm (n = 13), width 2.08–2.83 μm. The axial area is narrow and linear. Central area forming a barely visible in LM rounded, broad fascia with one to two slightly shortened striae near the valve margin. Scanning electron microscopy (SEM) (Figs 12–16): ―Raphe filiform with very slightly expanded proximal raphe endings and sickle-shaped distal raphe endings, continuing onto the valve mantle (Figs. 12–13). Internally, proximal raphe endings deflected (Fig. 14), and distal endings terminating in small helictoglossae (Figs. 14–16). Transapical striae parallel towards the apices to very weakly radiate at the middle portion, 5–14 in 10 μm. Virgae wider than the striae in the central portion of the valve (Fig. 15). Striae interrupted near the valve face/mantle junction, composed of 2–4 large (relative to valve size) areolae, covered on the outside by a porous hymen. Type: ― BRAZIL. Rio Grande do Sul, Osório, Emboaba coastal lake, 29°58’049”S 050°13’180”W, coll. date 16.February.2022, leg. Luciane O. Crossetti (holotype slide ICN-212275, Fig. 1–5 represent the holotype). Etymology: ―The epithet originates from the Tupi language, spoken by several indigenous groups in Brazil. Tupi has had a lasting influence on Brazilian Portuguese, and many words of Tupi origin, including “ mirim ”, remain in common usage today. In Tupi, “ mirim ” means “small” and is used in reference to the valve’s small dimensions. Ecology & associated diatom flora:— Chamaepinnularia mirim was a rare species in terms of relative abundance, representing 1.50% of the 534 valves counted in the type sample from Emboaba coastal lakes. Across the other sampled coastal lakes, its average relative abundance was 0.66% (range 0.37–1.50%), indicating a consistent low relative abundance throughout the studied lakes. The sample was collected by emergent macrophyte Schoenoplectus californicus (C.A. Mey.) Soják (1972: 127) during the austral summertime. The environmental conditions where the new species was found showed little variation. Water temperature with an average of 27 °C (± 1), transparency 60 cm (± 24), pH 7.5 level (± 0.513), electric conductivity 137 mS/cm (± 74.20), total nitrogen 0.921 mg L- 1 (± 0.729), and total phosphorus 0.129 mg L- 1 (± 0.367). Across the eight analyzed coastal lakes, the diatom species that most frequently co-occurred with C. mirim were Pseudostaurosiropsis connecticutensis E.A. Morales (2001: 117) with 12.50% relative abundance, Nitzschia palea (Kützing) W. Smith (1856: 107) with an average of 3.19% relative abundance, and Staurosira construens Ehrenberg (1843b: 424) with 1.54% relative abundance. Thus, these species were consistently present in the coastal lakes were C. mirim was found, suggesting potential similarities in their environmental requirements. Figures 1–16: Chamaepinnularia mirim M.G.Junqueira, L.O.Crossetti & C.E.Wetzel, sp. nov. Light and scanning electron microscopy. Figs 12–13: External views showing the straight raphe, with distal ends bent to the same side, the central silica nodule, and slightly radiate striae. Areolae occlusions at the same level of the valve surface. Figs 14–16: Internal views showing three large areolae interrupted by the silica deposition along the apical plane. Valves showing the radiate striae composed by three or four areolae and the straight raphe, with distal ends bent towards the same side. Specimens from slide ICN212275. Figs 1–5: ×1500; Figs 6–11: ×3000. Taxonomic comments:— Despite Chamaepinnularia mirim not having one elongated areolae as commonly found in the genus Chamaepinnularia (Lange-Bertalot & Metzeltin 1996, Wetzel et al. 2013), the new species shows morphological similarity with two species described for the genus (Table 1). First, C. aerophila first reported for the Île Amsterdam, and in small caves on Île de la Possession (Antarctic and sub-Antarctic regions) (Van de Vijver & Cox, 2013), is similar regarding by having valves lanceolate to linear-lanceolate, central area capitate, broadly rounded apices, yet is distinct mainly by having a greater length (7–12 μm), lower dense striation, and striae that are composed by one single large and rounded areola on the valve face (Table 1). Second, C. hassiaca (Krasske 1925: 47) Cantonati & Lange-Bertalot (2009: 228) is also similar by having valves lanceolate to linear-lanceolate with a usually inflated central area and capitate to subcapitate, broadly rounded apices, but differs by having only one areola per stria in the valve face (Table 1). However, the group of species showing the most similar patterns in terms of size and shape are the ones described and discussed by Lai et al. (2019) and Wetzel & Ector (2016). Chamaepinnularia thermophila (Manguin in Bourrelly & Manguin 1952: 59) C.E. Wetzel & Ector (2016: 96) and Chamaepinnularia tongatensis, are also species with diminutive forms, with size ranging from 7.2–8.0 μm in length and 2.5–3.0 μm in width for C. thermophila, and 10–14 μm in length and 3–3.5 μm in width for C. tongatensis (Table 1). Both species differ from C. mirim, which has wider central inflation on the median portion of the valve, being wider to the apices, also having a more radiant striation pattern (Table 1). Furthermore, C. thermophila is a rare species presented in thermal springs with warm waters (20–60 °C), alkaline pH (7.26–8.00), medium to high electrical conductivity (570–1558 μS cm−1), nitrates (200–2932 μg L− 1), and can be relativey abundant in a few tropical sites (Lai et al. 2019). Therefore, the occurrence of the C. thermophila in environments with different conditions in water temperature and eletrical conductitivy seems unusual, however, it could indicate a broader ecological distribution of the species. Lai et al. (2019) presented the first framework outlining the geographic distribution and ecology of both C. thermophila and C. tongatensis, drawing on both existing literature and new data based on the type materials. They also pointed out the potential synonymy between the two species. However, this finding should be approached with caution, particularly given the scarcity of studies in neotropical regions, where unexplored biodiversity remains largely undocumented. This gap in research highlights the need for further investigation to fully understand the species distributions. Our discovery expands the know range of diatom diversity in neotropical ecosystems, offering new insight into the ecological adaptability and distribution of Chamaepinnularia genus in tropical environments. Furthermore, from a biogeographical perspective, the description of Chamaepinnularia mirim makes a substantial contribution to closing the evolutionary gap within the genus. It sheds light on the genus’s biogeographical patterns, potentially linking the tropical ecosystems of South America with both temperate and tropical regions, where morphologically similar species like C. thermophila and C. tongatensis are found. This discovery not only deepens our understanding of the genus’s ecological adaptability but also emphasizes the broader distribution patterns that may span diverse environments. (2025-11-11)
***This entry has been automatically imported via OpenAlex by LIST harvest scripts. Please refer to https://doi.org/10.5281/zenodo.18413881 for the original and latest version of the publication*** (2026-07-01)
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