Achnanthidium guarulhense M.B.A.Silva, Osti & Marquardt

Silva, Mariana B. A., Osti, João A. S., Bicudo, Denise C. & Marquardt, Gisele C., 2024, Achnanthidium guarulhense sp. nov. (Achnanthidiaceae, Bacillariophyta), a new diatom species from a Conservation Unit in Southeast Brazil, Phytotaxa 640 (3), pp. 275-283 : 277-279

Achnanthidium guarulhense M.B.A.Silva, Osti & Marquardt , sp. nov. ( Figs 1–49 ).

Description—LM ( Figs 1–40 ): Frustules are usually solitary, girdle view rectangular, slightly arched, with apices slightly recurved to the rapheless valve ( Figs 38–40 ). Valve are linear-elliptic to linear-lanceolate to lanceolate, with broadly round to sub-rostrate ends ( Figs 1–37 ); 17.0–20.0 μm long and 3.0–4.0 μm wide (n= 40). Striae not discernible, except in the middle part of the valve where a few separated slightly radiated striae (2–5) become resolvable due to a wider spacing ( Figs 1–37 ). Raphe valve ( Figs 1–29 ): Raphe filiform straight. Axial area linear-lanceolate, expanding to a small apically a linear-elliptic central area located between the proximal raphe ends ( Figs 1–29 ). Rapheless valve ( Figs 30–37 ): slightly convex with a narrow and linear axial area ( Figs 31, 35 , and 36), sometimes expanding to a small, elliptic central area ( Figs 30, 32 , and 34).

SEM ( Figs 41-49 ): Raphe valve slightly concave ( Figs 48–49 ). The rapheless valve slightly convex ( Figs 48–49 ). Distal raphe ends terminating after the last stria at the mantle ( Fig. 41 ). Central and terminal raphe fissures straight ( Fig. 41 ). Striae uniseriate, radiate throughout, 30–35 in 10 μm, composed of 3–4 rounded areolae ( Figs 41–47 ), sometimes with slit-like areolae near the valve margin ( Figs 41–47 ). Externally, axial area narrowly linear and silicified, widening towards the central area ( Fig. 41 ). Internally, proximal raphe ends slightly curved in opposite directions ( Figs 42–44 ), and distal raphe ends terminate as helictoglossae ( Fig 42–43 ). Areolae occluded with fine a hymen ( Fig. 44 ). The mantle has one row of slit-like areolae ( Figs 48–49 ).

Type: BRAZIL. State of São Paulo: Guarulhos, phytoplankton from Negro Lake , 23°18’20” S, 46°23’26” W, 1500 m, 1 June 2020, Collector(s): João S. Osti, Edna Ferreira & Gisele C. Marquardt. (holotype here designated, permanent slide: UPCB 105117 , Universidade Federal do Paraná, Brazil, UPCB) .

Etymology: The specific epithet refers to the type locality, city of Guarulhos.

Ecology and associated diatom flora: The new species is associated, among others, with Ulnaria delicatissima var. angustissima (Grunow) Aboal & P.C.Silva (2004: 361) , Ulnaria ulna (Nitzsch) Compère (2001: 100) , Achnanthidium sp. , Aulacoseira ambigua (Grunow) Simonsen (1979: 56) , and Spicaticribra rudis (Tremarin, T.Ludwig, V.Becker & Torgan) in A. Tuji, Leelahakriengkrai & Peerapornpisal (2012: 146). We cannot confirm whether Achnanthidium guarulhense sp. nov. is a planktic diatom species since no other substratum (periphytic or benthic material) was sampled.

Achnanthidium guarulhense sp. nov. was recorded in the phytoplankton community of a shallow lake with soil walls and bottom during the spring. The taxon was found representing 20% of the phytoplankton community. Cyanobacteria, Chlorophyceae, and Trebouxiphyceae were the most abundant classes of the community and contributed 33%, 18%, and 15%, respectively, of the relative abundance.

The following limnological features were presented at the time of the sample: water temperature 19.17 ºC, pH 6.17, electrical conductivity 72.37 μS. cm-1, dissolved oxygen 8.67 mg.L- 1, turbidity 10.00 NTU, and Secchi transparency 1.85 m. According to the trophic state index, Negro Lake is described as an oligo-mesotrophic system ( Osti et al. 2022).

Figures

FIGURES 1–40. LM images of Achnanthidium guarulhense sp. nov. of the (UPCB 105117) holotype slide from Negro Lake, Guarulhos, state of São Paulo. 1–29. LM views of raphe valves. 30–37. LM views of rapheless valves. 38–40. LM of girdle view. LM scale bar = 10 μm.

FIGURES 41–49. SEM images of Achnanthidium guarulhense sp. nov. of the (UPCB 105117) holotype slide from Negro Lake,Guarulhos, state of São Paulo. 41. SEM external view of raphe valve showing striation pattern, and axial and central areas. 42–44. SEM internal view of the raphe valve. 44. Note the detail of areolae occlusions. 45–46. SEM external view of the rapheless valve. 47. SEM internal view of the rapheless valve. 48–49. SEM showing the girdle view. SEM scale bar = 3 μm; 44 =1 μm; 46, 49 = 4 μm.