Craspedostauros lateralis Al-Handal, Ashworth and A. Wulff, 2024

Al-Handal, Adil Y., Ashworth, Matt P. & Wulff, Angela, 2024, A new species of Craspedostauros (Bacillariophyceae) from the west coast of Sweden, with taxonomic and ecological notes on Craspedostauros laevissimus, Botanica Marina (Warsaw, Poland) 67 (1), pp. 51-60 : 52-54

Craspedostauros lateralis Al-Handal, Ashworth and A. Wulff sp. nov. ( Figures 1–9 , 18–27 )

Description: Light microscopy (LM) observations ( Figures 1–9 ): Valves are linear to linear-lanceolate with a triangular constriction in the middle ( Figures 1 and 3 ). Valve margins are gradually tapering to rounded apices. Smaller valves appear narrowly elliptic ( Figure 8 ). Valves are 34–81 μm long and 8.5–10 μm wide in mid-valve (n = 35).

The axial area is very narrow and linear. The central area is narrow, appearing as a laterally dilated diamond and forming fascia reaching the constricted valve margin. Raphe is faintly visible in LM, particularly near the central area, due to valve curvature. Striae discernible in LM, 19–25 in 10 μm ( Figures 6 and 8 ). The junction line between valve face and mantle is either invisible or appear as a very narrow line on both sides of the valve ( Figure 7 ). Scanning electron microscopy ( SEM) observations ( Figures 18–27 ): Externally, the valve face is weakly undulate with a gradually bending mantle. The stauros and fascia are extended at the constricted part of the valve to form a distinctive silica flap ( Figure 27 ). The valve poles at the distal raphe ending are devoid of striae except on the apical part of the mantle where few rows of areolae are seen ( Figure 23 ). The axial area is very narrow and straight ( Figure 19 ). The central area is narrow and transversely elongated, slightly raised above valve face which forms a facia reaching valve margin ( Figure 21 ). The raphe is filiform and slightly undulating towards the central area but becoming straight on the rest of the valve ( Figures 21 and 23 ). The proximal raphe endings are straight and elongated ( Figure 21 ), the distal endings are bent at 90° angle ( Figure 23 ). There are two irregular, linear lanceolate hyaline areas marking the junction line between valve face and the mantle ( Figure 21 , arrows). These are wide around the central area and becoming very straight and narrow towards the apices. The valve part between the hyaline areas and the axial area is slightly depressed ( Figures 21 and 25 ). The striae are uniseriate, parallel at the centre and convergent near the apices ( Figure 23 ). The cribrate areolae are larger on both sides of the axial area, 48–50 in 10 μm, slightly becoming smaller towards the lateral hyaline areas ( Figures 21, 23 , and 25). Cribra are formed of 4–5 small peripheral pores ( Figure 25 ), central pores are absent. Internally, the area between the junction lines is depressed and formed of elongated areolae ( Figures 22 and 24 ). These elongated areolae resulted from combing 2–4 adjacent quadrangular areolae ( Figure 24 ). The central area widens transversely and apically at the valve margin forming a spectacular triangular fascia ( Figure 20 , arrow). The stauros is distinct and occupies the middle part of the central area between the junction lines ( Figure 20 ). The central part of the stauros is dome-like helictoglossa which is interrupted by a blunt groove connecting the raphe proximal endings ( Figure 27 , arrow). The distal raphe endings are weakly bent and terminate on a shallow helictoglossae ( Figure 22 ).

Holotype: Permanent slide containing frustules of C. lateralis sp. nov. are deposited in the Botanischer Garten und Botanischer Museum ( BGBM), Berlin, Germany under accession B 40 0046319 . Holotype illustrated in Figures 1–8 . Phycobank registration http://phycobank.org/103978.

Type locality: Saltholmen , west coast of Sweden (57° 39′ 32″ N, 11° 50′ 21″ E) .

Etymology: The epithet refers to the lateral hyaline areas on both sides of the axial area.

Ecology: Craspedostauros lateralis is a marine species, found epiphytic on the brown macrophyte Mesogloia sp. attached to rocks. Temperature at time of collection was 10.5 °C and salinity 27 psu. It was a rare species, constituted 0.8 % of the total diatom community epiphytic on Mesogloia sp. Other diatom taxa found associated with C. lateralis were Achnanthes brevipes C. Agardh (12.6 %), Tabularia fasciculata (C. Agardh) D.M. Williams and Round (11.3 %), Entomoneis paludosa (W. Smith) Reimer (6.2 %), Haslea spicula (Hickie) Bukhtiyarova (3.4 %), Amphora spp. (2.5 %), Nitzschia sigma (Kützing) W. Smith (1.8 %), Surirella sp. (1.1 %), and several other taxa small taxa of Navicula and Nitzschia .

Differential diagnosis: The marginal hyaline areas differentiate C. lateralis from other taxa sharing similar narrow and constricted valves. This feature is not always visible in LM and C. lateralis might be confused with related species such as C. amphoides (Grunow et A. Schmidt) E.J. Cox and C. macewanii Majewska et Ashworth. It can be distinguished from C. amphoides by having larger valves (34–85 μm compared to 28–45 μm), from macewanii by its stria density (30–32 compared to 28–31 in 10 μm) and from C. amphoides by having larger valves and denser striae. Ultrastructural differences with related taxa are discussed below.

Figures

Figures 1–17: Light micrographs of Craspedostauros lateralis sp. nov. and C. cf. laevissimus of different sizes. (1–9) Craspedostauros lateralis. (1–8) Showing the distinct constriction of the valve and the shape of the stauros. (9) A small valve with elliptic outline.(10–17) Craspedostauros cf.laevissimus. (10–12) Valves with parallel margins. (13, 14) Valves with slightly inflated valve halves. (15) Valve with slightly swollen at the centre. (16) Small elliptic valve. (17) Frustule in girdle view showing constriction and cingular bands. Scale bars = 10 μm.

Figures 18–27: Scanning electron micrographs of Craspedostauros lateralis sp. nov. (18) Valve in internal view. (19) External side of the valve. (20) Middle part of the valve interior showing the depressed areas on both sides of the axial area (arrows) and the characteristic triangular constriction of the valve which is an extension of the central area (fascia). (21) The two irregular hyaline areas (arrows) which form the junction line between valve face and the mantle. (22) Internal side of the valve pole exhibiting the distal raphe ending. (23) External side of the valve pole with the curved distal raphe ending.(24) Elongated areolae on both sides of the axial area with numerous cribral pores. (25) External openings of the areolae with 4–5 peripheral cribral pores. (26) Valve in girdle view. (27) Internal side of the valve showing the folded marginal silica flap and the dome-like central helicoglossa (arrow).Scale bars:18,19,26) 8 μm; (20,21,22,23, 27) 2 μm; (24, 25) 0.8 μm.