Frankophila dalevittii Van de Vijver & Goeyers, 2020

Vijver, Bart Van De, Ballings, Petra & Goeyers, Charlotte, 2020, Frankophila dalevittii, a new freshwater diatom (Bacillariophyta) from Campbell Island, Phytotaxa 429 (1), pp. 57-64 : 58-59

Frankophila dalevittii Van de Vijver & Goeyers sp. nov. ( Figs 1–39 )

LM ( Figs 1–30 ): Frustules rectangular in girdle view, forming long chains of several tens of frustules, connected by relatively large, interdigitating linking spines ( Figs 1–4 ). Valves linear-elliptical to elliptical and even elliptic-lanceolate. Smallest specimens almost rounded. Apices never protracted, always broadly rounded. Elliptic-lanceolate specimens with less broadly rounded apices. Valve dimensions (n=50): length 4–15 µm, width 3–5 µm. One initial valve observed: length 33 µm, width 6 µm. Axial area moderately wide, almost 1/3 of total valve width, lanceolate to linear-lanceolate. Central area lacking. Striae parallel in the valve centre becoming distinctly radiate towards the apices, 11–12 in 12 µm. Areolae not discernible in LM. SEM ( Figs 31–39 ): Girdle composed of at least two open, non-perforated copulae ( Figs 31 , 33 ). Copulae often covered by irregular pattern of small ridges and granules ( Figs 31, 32 ). Mantle very broad with clearly undulating edge ( Fig. 32 ). Lower part of the mantle hyaline, covered with fine silica granules ( Fig. 32 ). Frustules connected to each other via well-developed, interdigitating linking spines ( Figs 31, 32 , 34 ). Spines solid with dichotomously branching ends ( Fig. 34 ), located on the virgae between the striae ( Figs 35, 36 ). External raphe vestiges absent ( Figs. 35, 36 ) although shallow depressions occasionally observed where slits were expected ( Figs 35, 36 , arrows). Striae composed of two rows of rather large, rounded areolae, terminating near the axial area by one areola. Striae continuing shortly but uninterruptedly onto the valve mantle. Rimoportulae and apical porefields absent ( Figs 36, 38 ). Internally, short raphe slits visible near the valve apices ( Figs 37, 38, 39 , arrows), <0.5 µm long. Areolae located in deep grooves ( Figs 37, 38 ).

Type:—Perseverance Harbour east of Moubray Hill, Campbell Island, sub-Antarctic Region, sample BAS 303 (leg. D. Vitt, coll. date: 12/01/1970) (holotype BR!, slide no. 4574, isotype PLP! slide no. 367, University of Antwerp, Belgium).

Etymology:—the species is named after Dr. Dale Vitt (Southern Illinois University Carbondale, USA), who collected in the austral summer of 1969–1970 the moss samples used in this study. His collection forms the base of an important contribution to the biogeography and biodiversity of the non-marine diatoms of the sub-Antarctic islands in the southern Pacific Ocean.

Ecology:— Frankophila dalevittii was observed in three moss samples on Campbell Island. The largest population (up to 10% of all diatom valves in the sample) was found in a Racopilum strumiferum vegetation on wet rock under a large overhang in a cave next to sea. The accompanying diatom flora is composed of several melosiroid taxa (that are currently being described as new taxa, Goeyers & Van de Vijver, unpubl. res.), Rhopalodia sp. , Diatomella balfouriana Greville (1855: 259) and Diatomella colonialis Van de Vijver & Le Cohu (2017: 282) .

Figures

FIGURES 1–32. Frankophila dalevittii Van de Vijver & Goeyers sp. nov. Light microscopy (1–30) and scanning electron microscopy (31–32) views. Holotype population from Campbell Island (sample BAS303). 1–4. Frustules connected via linking spines to form long, band like colonies. 5. Possible initial valve. 6–30. Valve views showing the broad range of valve dimensions. 31–32. Two colonies of three (fig. 31) and two (fig. 32) frustules connected by linking spines. Scale bars represent 10 µm.

FIGURES 33–39. Frankophila dalevittii Van de Vijver & Goeyers sp. nov. Scanning electron microscopy views. Holotype population from Campbell Island (sample BAS303). 33. SEM detail of several frustules connected by linking spines showing the girdle structure and the lack of an apical porefield. 34. SEM detail of the interdigitating linking spines. Also note the irregular siliceous ridges on the girdle band. 35–36. SEM external valve face views. Note the presence of the linking spines and the reduced external raphe slits (arrows). 37–38. SEM internal valve face views of two entire valves showing the reduced internal raphe slits (arrows). 38. SEM detail of the internal raphe slit. Scale bars represent 10 µm except for Figs 33, 34 & 39 where scale bars = 1 µm.