Gomphosphenia minima C. Delgado, S. Blanco, L. González-Paz & S.F.P. Almeida, 2022

González-Paz, Lorena, Almeida, Salomé F. P., Blanco, Saúl & Delgado, Cristina, 2022, A new species of an unexplored diatom genus: Gomphosphenia minima sp. nov. (Cymbellales, Rhoicospheniaceae), Phytotaxa 554 (2), pp. 135-148 : 138

Gomphosphenia minima C. Delgado, S. Blanco, L. González-Paz & S.F.P. Almeida sp. nov. ( Figs 2–7 LM, Figs 20–26 SEM)

Description:— Frustules in girdle view wedge-shaped ( Fig. 24 ). Valves slightly heteropolar, narrowly clavate to linear-lanceolate with narrowly rounded and not protracted headpole and footpole ( Figs 2–7 , 20, 23, 25, 26 ). Largest width near the mid-valve. Valve dimensions (n = 12): length 5.0–8.0 µm, width 2.2–3.0 µm. Axial area rather wide, lanceolate, widening slightly towards the central area ( Figs 20, 23, 25, 26 ). Raphe is straight with slightly expanded drop-like proximal endings ( Figs 21–23 ). Internally, proximal raphe endings are short, unilaterally deflected as small hooks ( Figs 20, 22 ). Distal external raphe endings are very short, straight, slightly expanded into drop-like pores and not extended into the valve mantle ( Figs 23, 25, 26 ). At LM view, striae are difficult to resolve due to the small valve size ( Figs 2–7 ). Transapical uniseriate striae weakly radiate, becoming almost parallel mid-valve, 18–25 striae in 10 μm. Each stria is composed of a single transversely elongated areola both externally and internally ( Figs 20–23, 25, 26 ). A row of individual pores (elongated in the pervalvar direction) is located on the valve mantle in girdle view ( Fig. 24 ).

Type:— PORTUGAL. Municipality of Coimbra, district of Coimbra, Centro region, Coimbra subregion: Candal stream, 40°4´44”N, 8°12´10”W, 10th February 2012 (holotype BM 81051 ! Natural History Museum, London, UK = Fig. 5 ; isotype: GDA 69158 University of Granada Herbarium , Granada, Spain) .

Etymology:— The specific epithet minima (from the Latin minimum: very little, very least) refers to the size of this taxon.

Distribution and ecology:— Gomphosphenia minima was found in a few of the studied samples. From the 48 samples in the Candal stream, it only occurred in two samples from the same sampling point collected in February 2012 with an average abundance of 0.7 %. It was present in oligotrophic waters (370–910 μg∙L- 1 of nitrate), with neutral pH values (7.7), low electric conductivity (26.3–26.8 μS∙ cm-1) and low water temperature (3.8–8.1 ºC).

Associated species: —The diatom assemblage of the type locality (Coimbra) was composed of different species such as Planothidium lanceolatum (Brébisson ex Kützing) Lange-Bertalot (1999: 287) (27.1 %; Figs 7–14 ), Eunotia minor (Kützing) Grunow (in Van Heurck 1881, figs 20–21) (17.3 %; Figs 19–22 , 45 ), Planothidium frequentissimum (Lange-Bertalot) (in Lange-Bertalot 1999: 282) (16.8 %; Figs 15–18 , 41 , 42 ) and Sellaphora nigri (De Notaris) Wetzel & Ector (2015: 221 , Figs 319–393) (11.4 %; Figs 23–33 , 43, 44 ).

Figures

FIGURES 2–19. LM micrographs. 2–7. Gomphosphenia minima C. Delgado, S. Blanco, L. González-Paz & S.F.P.Almeida sp. nov. 8–15. Planothidium lanceolatum. 16–19. Planothidium frequentissimum. Scale bar = 10 µm.

FIGURES 20–26. SEM micrographs of Gomphosphenia minima C. Delgado, S. Blanco, L. González-Paz & S.F.P. Almeida sp. nov. 20. Internal valve view showing the raphe ending and the transapical uniseriate striae. 21. External view of the central area showing the raphe ending slightly expanded into drop-like pores. 22. Internal view of the central area showing the raphe ending curved to one side. 23. External view of the valve showing the striae composed of a single areola. 24. Girdle view of the entire frustule showing the mantle striae composed by row of individual pores (elongated in the pervalvar direction). 25. External valve showing the narrowly rounded headpole. 26. External valve showing the narrowly rounded footpole. Scale bar = 1 μm (Figs 20–26).

FIGURES 42–46. SEM micrographs. 42–43. Planothidium frequentissimum. 42. Internal valve view showing the roundish cavum with the narrow opening. 43. External view showing the striae composed of three rows of small rounded areolae, and straight raphe branches with expanded drop–like proximal raphe endings. 44–45. Sellaphora nigri. 44. External valve view showing the bow tie-shaped central area and the ‘tear-drop’ shaped proximal ends of the raphe. 45. External valve view showing the areoles closest to the raphe being larger and slightly angular, square or nearly rounded, while the marginal areoles become smaller and more circular. 46. Eunotia minor, girdle view. Scale bar = 3 µm.

FIGURES 27–41. LM micrographs. 27–30. Eunotia minor. 31–41. Sellaphora nigri. Scale bar = 10 µm.