Achnanthes kohleriana Kopalová, Zidarova & Van de Vijver, 2016

Kopalová, Kateřina, Zidarova, Ralitsa & Vijver, Bart Van De, 2016, Four new monoraphid diatom species (Bacillariophyta, Achnanthaceae) from the Maritime Antarctic Region, European Journal of Taxonomy 217, pp. 1-19 : 3-7

Achnanthes kohleriana Kopalová, Zidarova & Van de Vijver sp. nov.

Figs 1–24

Etymology

The species is named after our friend and colleague Dr. Tyler Kohler (Charles University in Prague and University of Boulder, Colorado, USA) in recognition of his diatom ecology work in the Dry Valleys of the Antarctic Continent.

Type

Deception Island, South Shetland Islands, Antarctica, sample D13 (62°58′24.5″ S 60°43′03.2″W) (leg. R. Zidarova), coll. date: 21 Jan. 2013 (holo-: slide no. BR–4436; iso-: slide PLP–292, University of Antwerp, Belgium).

Description

Light microscopy ( Figs 1–13 )

Frustules in girdle view bent, with concave raphe valve and convex rapheless valve ( Fig. 13 ). Valves linear to linear-elliptic, with almost straight to weakly concave in the middle valve margins. Valve apices broadly rounded, not protracted. Valve dimensions (n = 24): length 38–45 µm, width 9.0– 10.5 µm. Raphe valve ( Figs 1–6 ): raphe distinctly lateral, curved. Proximal raphe endings deflected to one side terminating in drop-like expanded pores. Distal raphe fissures elongated and hooked. Axial area 1/4–1/5 of the valve width, almost linear, following the curvature of the raphe, not or only slightly widening toward the central area. Central area forming a rectangular to bow-tie-shaped fascia, lacking any striae near the margins. Transapical striae weakly to moderately radiate in the middle, becoming more radiate toward the apices, 11–12 in 10 µm. Areolae well discernible in LM, rounded, c. 14–18 in 10 µm. Rapheless valve ( Figs 7–12 ): rapheless sternum narrow, located close to the valve margin. Striae parallel at the valve middle, becoming radiate toward the apices, 10–11 in 10 µm. Areolae well discernible in LM, rounded, c. 14–18 in 10 µm.

Scanning electron microscopy ( Figs 14–24 )

Raphe valve ( Figs 14–19 ): valve face weakly concave in the middle. Apices presenting a rather larger hyaline zone ( Figs 14, 16 ). Raphe slightly curved with tear-drop-shaped, weakly deflected proximal raphe endings, not extending in the central area ( Figs 14, 17 ). Distal raphe fissures running a deep groove, hooked, elongated, continuing onto the mantle, terminating beyond the last striae ( Figs 14, 16 ). Striae uniseriate, composed of almost rounded areolae with slightly recessed foramina, occluded by cribra with rounded perforations ( Fig. 15 ). Small pseudosepta present near the valve apices ( Fig. 19 ). Internally, proximal raphe endings strongly hooked backwards toward the poles ( Fig. 18 ). Distal raphe endings straight, finishing onto small helictoglossae ( Fig. 19 ). Striae separated by strongly thickened virgae ( Fig. 19 ). Areolae with rounded foramina and recessed cribra ( Fig. 19 ). Rapheless valve ( Figs 20–24 ): valve face weakly convex ( Fig. 20 ).A strongly thickened hyaline marginal ridge present at the valve face/ mantle junction ( Figs 20, 21 ). Spines absent. Rapheless sternum narrow, located near the valve margin ( Fig. 21 ), internally well discernible as a narrow hyaline line close to the valve margin ( Fig. 24 , arrows). Terminal orbiculi present on the valve mantle near the apices, occluded by a single, structureless silica flap ( Fig. 23 ). Striae uniseriate on the valve face, becoming bi-seriate on the valve mantle ( Fig. 23 ). Each stria composed of recessed rounded areolae, occluded by cribra with rounded or irregular perforations ( Fig. 22 ). Internally, striae separated by strongly thickened virgae ( Fig. 24 ). Areolae with rounded openings with noticeably recessed cribra ( Fig. 24 ). Girdle composed of several open copulae, bearing a single row of rounded areolae, occluded by cribra ( Fig. 20 ).

Ecology and distribution

So far Achnanthes kohleriana sp. nov. has been observed with certainty on several islands of the South Shetland archipelago (Livingston Island, Deception Island and King George Island). The largest population was found on Deception Island among wet mosses growing on a rock, located inland and far from the influence of sea sprays and with no nutrient input from sea birds or seals suggesting that the species is typically aerophilic. Other taxa present in the sample include Humidophila keiliorum Kopalová in Kopalová et al. (2015) , H. deceptionensis Kopalová in Kopalová et al. (2015) , Stauroneis pseudomuriella Van de Vijver & Lange-Bert. in Van de Vijver et al. (2004) , S. pseudoschimanskii Van de Vijver & Lange-Bert. in Van de Vijver et al. (2004) and several Luticola species.

Genus Planothidium Round & Bukht. ( Round & Bukhtiyarova 1996)

Figures

Figs 1–13. Achnanthes kohleriana Kopalová, Zidarova & Van de Vijver sp. nov. Light micrographs of the type population from Deception Island (South Shetland Islands, Antarctica). 1–16. LM views of raphe valves. 7–12. LM views of rapheless valves. 13. LM view of a girdle view. Scale bar represents 10 µm.

Figs 14–19. Achnanthes kohleriana Kopalová, Zidarova & Van de Vijver sp. nov. Scanning electron micrographs of the type population from Deception Island (South Shetland Islands, Antarctica). 14. SEM external view of an entire raphe valve. 15. SEM external detail of the areolae with the typical cribrate structure. 16. SEM external view of the distal raphe ending. 17. SEM external detail of the central area. 18. SEM internal detail of the central area showing the hooked proximal raphe endings. 19. SEM internal view of an entire raphe valve. Scale bars represent 10 µm for Figs 14 & 19, 1 µm for Fig. 15 and 5 µm for Figs 16–18.

Figs 20–24. Achnanthes kohleriana Kopalová, Zidarova & Van de Vijver sp. nov. Scanning electron micrographs of the type population from Deception Island (South Shetland Islands, Antarctica). 20. SEM girdle view of an entire frustule. 21. SEM external view of a raphe valve. 22. SEM external detail of the areolae with the typical cribrate structure. 23. SEM external detail of the apex with the typical terminal orbiculus. 24. SEM internal view of an entire rapheless valve. Arrows show the rapheless sternum. Scale bars represent 10 µm for Figs 20, 21 & 24, 1 µm for Fig. 22 and 5 µm for Fig. 23.