Planothidium incuriatum C.E.Wetzel, Van de Vijver & Ector, 2013

Wetzel, Carlos E., Hoffmann, Bart Van De Vijver Lucien & Ector, Luc, 2013, Planothidium incuriatum sp. nov. a widely distributed diatom species (Bacillariophyta) and type analysis of Planothidium biporomum, Phytotaxa 138 (1), pp. 43-57 : 49-51

Planothidium incuriatum C.E.Wetzel, Van de Vijver & Ector sp. nov. ( Figs 19–36 , 51–89 )

Light microscopy ( Figs 19–36 , 62–79 ): — Valves lanceolate to elliptic-lanceolate with convex margins and rostrate, protracted apices. Valve dimensions (n=30): length 18.0– 25.4 µm, width 6.4–7.0 µm. Rapheless valve ( Figs 19–27 , 62 – 70 ): Axial area narrow, straight linear. Central area with a unilateral large horseshoe-shaped hyaline area with a cavum clearly visible. On the opposite side, striae either not shortened sometimes slightly shortened striae forming hence a small circular area ( Fig. 24 ). Striae weakly radiate throughout the entire valve. Between 13 and 15 striae in 10 µm measured at the central part of the valve opposite to the unilateral expansion. Raphe valve ( Figs 28–36 , 71–79 ): Axial area narrow, linear, widening near the central area. Central area rectangular to slightly rounded, bordered on each side by usually two up to three shortened striae. Raphe branches straight with expanded, drop-like proximal raphe endings. Distal raphe fissures unilaterally deflected. Striae radiate throughout the entire valve, 13–15 in 10 µm. Areolae not discernible in LM.

Scanning electron microscopy ( Figs 51–61 , 80–89 ): — Rapheless valve: striae composed externally of two to three rows of small rounded areolae ( Figs 51, 60, 61 , 80, 86 ), the middle row being smaller than the two parallel outer rows ( Figs 61 , 86 ). Striae near the axial area often composed of two ( Figs 51, 60 ), sometimes three ( Figs 61 , 86 ) rows of areolae near the valve mantle. Striae continuing shortly on the valve mantle ( Figs 61 , 80 ). Raphe valve: striae broader than the virgae, composed of three ( Fig. 56 ) to four ( Figs 83, 88 ) rows of rounded areolae ( Fig. 89 ). Striae internally sunken between raised virgae ( Figs 55 , 81–82 ). Areolae internally covered by individual hymenes ( Fig. 55 ). Proximal external raphe endings expanded ( Figs 53, 56 , 83 ). Distal raphe fissures bent, continuing shortly onto the valve mantle ( Fig. 58 ). Internally central nodule raised, with proximal raphe endings not enlarged, deflected to opposite sides ( Figs 55 , 87 ). Distal raphe ends terminate internally with inconspicuous helictoglossae ( Fig. 84 ). Shallow rounded irregular depressions also present in the central and axial area ( Figs 51 , 80, 86 ). Groups of two small rounded poroids located externally in the valve mantle ( Figs 88–89 ).

Holotype (designated here): — FRANCE. Île de France Region ( Yvelines ), Magny-les-Hameaux : ‘ Croix au Buis’ creek, Yvette River basin (48°43'5.016"N latitude 2°4'24.494"E longitude). Leg. Jeanne Rigaut ( GREBE, Groupe de Recherche et d'Etudes Biologie et Environnement , Lyon, France), 25/04/2012 . Holotype depicted in Fig. 21 , deposited at the National Botanic Garden, Meise, Belgium (slide BR-4315).

Paratype (designated here):— BRAZIL. Rio Grande do Sul, Sinimbú, Pardinho Falls (‘ Salto do Pardinho’ ), Pardinho River , Rio Pardo hydrographical basin, 15/01/2004; Leg. C.E. Wetzel, deposited at the National Botanic Garden, Meise, Belgium (slide BR-4316) .

Etymology: —From the Latin incúria, meaning lack of care or attention, neglect, carelessness, indifference.

Taxonomic remarks:— Besides the similarities with Planothidium biporomum , P. incuriatum is similar to P. infrequens Lange-Bert. & Rumrich in Rumrich et al. (2000: 212) described from the Andes mountain range in Chile (South America). Differences between the two species include the general outline of the apices being more apiculate and a lower stria density (11–13, not 13–15 in 10 µm as in P. incuriatum ) in the rapheless valve of P. infrequens . Planothidium incuriatum differs from P. biporomum by having rostrate extremities, while capitate and wider in P. biporomum , and by having more rows of areolae per stria in the rapheless valve. Planothidium incuriatum can also be confounded with P. frequentissimum [= Achnanthes lanceolata var. dubia f. minuta Grunow in Van Heurck, sensu Krammer & Lange-Bertalot (1991, pl. 44, figs 1–3)] from which it differs by having clearly larger cells, and Planothidium frequentissimum var. magnum (Straub) Lange-Bertalot (1999:292) [= Achnanthes rostrata var. magna Straub sensu Krammer & Lange- Bertalot (1991, pl. 44, figs 10–14)] which has clearly elliptical outline and smaller dimensions.

Planothidium incuriatum was also misidentified in the past as Planothidium rostratum sensu auct. non null. (see Table 1). However the lectotype of Achnanthes rostrata Østrup (1902 , p. 253, pl. 1, fig. 11) from Thailand ( Siam) illustrated by Krammer & Lange-Bertalot (1991, pl. 43, figs 1–4) has clearly smaller dimensions (length 9.3–14.0 µm, width 5.2–6.5), rounded valves with strongly rostrate extremities and a rounded central area in the raphe valve, and hence cannot be considered synonyms nor conspecific populations.

Zimmermann (1919) described Achnanthes lanceolata (Bréb.) Grunow var. brasiliensis C.Zimm. (1919: 99) from the Inhahúma River, a tributary of the Pacuí River, a major river on the right bank of the São Francisco River in the north of Minas Gerais ( Brazil). According to his drawings, the species has a quite similar valve outline compared to P. incuriatum and also possesses the unilateral expansion in the central area, with slightly radiate striae in the middle valve portion. Based on his drawings, all we can definitely state is that var. brasiliensis belongs to the genus Planothidium . Since Zimmermann’s specimens seems to be impossible to locate ( Gomes et al. 2012), a proper typification is not possible for the moment.

Figures

FIGURES 1–36. Planothidium biporomum and Planothidium incuriatum sp. nov. LM views. Figs 1–18. Planothidium biporomum. Valve views. Savannah River, Georgia, U.S.A., ANSP G.M.C. 3521(3). Figs 1–13. Rapheless valves. Figs 14–18. Raphe valves. Figs 19–36. Planothidium incuriatum sp. nov. Valve views. ‘Croix au Buis’ creek (Yvette River basin, Magny-les-Hameaux, France), BR- 4315. Figs 19–27. Rapheless valves. Figs 28–36. Raphe valves. Fig. 21. Holotype designated. ‘=’ signal indicates the valves of the same frustule. Scale bar represents 10 µm.

FIGURES 51–61. Planothidium incuriatum sp. nov. SEM views. ‘Croix au Buis’ creek (Yvette River basin, Magny-les-Hameaux, France), BR-4315. Fig. 51. External view of rapheless valve. Fig. 52. Internal view of raphe valve. Fig. 53. External view of raphe valve. Fig. 54. Internal view of rapheless valve. Fig. 55. Internal detailed view of raphe valve central area. Fig. 56. External detail of a raphe valve. Two reduced striae at both sides forming an irregular rectangular central area. Drop-like proximal raphe ends. Striae usually formed by three rows of areolae. Fig. 57. Detail of cavum aperture. Open border attached to the neighbour striae. Fig. 58. Detail of raphe ends. Note the groups of two small areolae located in the valve mantle. Fig. 59. Open non-perforated and ligulated connective bands. Figs 60–61. Detail of striae usually triseriate from the rapheless valve, as well as the areolae located in the mantle. Scale bars: Figs 51–53 = 5 µm; Fig. 54 = 10 µm; Figs 55–56, 60 = 4 µm; Figs 57–59 = 3 µm; Fig. 61 = 2 µm.

FIGURES 62–79. Planothidium incuriatum sp. nov. LM views. Pardinho River, Rio Grande do Sul, Brazil. BR-4316. Figs 62–70. Rapheless valves. Figs 71–79. Raphe valves. Scale bar represents 10 µm.

FIGURES 80–89. Planothidium incuriatum sp. nov. SEM views. Pardinho River, Rio Grande do Sul, Brazil. BR-4316. Fig. 80. External view of rapheless valve. Note the similar areolae arrangement with the France population. Fig. 81. Internal view of raphe valve. Fig. 82. Internal view of rapheless valve with wide cavum aperture. Fig. 83. External view of raphe valve showing two reduced striae at both sides forming a rectangular central area. Fig. 84. Internal view of raphe valve reduced helictoglossae. Fig. 85. Internal view of rapheless valve apice. Fig. 86. Detail of central area of rapheless valve showing the triseriate striae, irregular rounded depressions along the apical axis and the external unilateral expansion. Fig. 87. Detail of central area of raphe valve. Figs 88–89. Detail of striae in raphe valve usually composed by 3–4 rows of areolae from the rapheless valve. Note the groups of two small areolae located in the valve mantle located at each stria. Scale bars: Figs 80–83 = 5 µm; Figs 86–87 = 4 µm; Figs 84–85, 88–89 = 2 µm.