Craspedostauros cf. laevissimus (West et G.S. West) Sabbe

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 : 55-56

Craspedostauros cf. laevissimus (West et G.S. West) Sabbe ( Figures 10–17 , 28–36 )

Description: Light microscopy ( LM) observations ( Figures 10–17 ): The frustules are rectangular in girdle view, constricted on the pervalvar axis, with slightly convex margins and several cingular bands ( Figure 17 ). The valves are linear to linear-lanceolate with broadly rounded apices, 21–58 μm long and 5.0–6.4 μm wide (n = 23). Larger valves either with parallel margins ( Figures 11 and 12 ) or rarely slightly irregular ( Figures 13 and 15 ). Smaller valves are elliptic ( Figure 16 ). The axial area is linear and very narrow. The central area is narrow, transversely expanded to the valve margins forming bow tie-shaped ( Figures 10–16 ). The raphe is filiform and straight. The raphe proximal endings are straight, distal endings are bent. Striae are very fine, parallel, 28–32 at mid-valve and 33–40 in 10 μm towards apices. Scanning electron microscopy ( SEM) observations ( Figures 28–35 ): Externally, the valve face is convex, gradually curving into a wide mantle ( Figures 32 and 34 ). Valve surface is slightly undulated between the mid-valve and poles and is more visible internally ( Figure 32 ). The axial area is narrow, follows valve curvature and widening at the apices into a transverse triangle ( Figures 29 and 33 ). The central area is rectangular, transversely dilated, with straight margins ( Figure 31 ). Middle part of the central area is elevated and rounded ( Figure 31 ). The raphe central endings are elongated, weakly bent to the same direction ( Figure 31 ). Distal raphe endings are curved and hooked, terminated shortly before the mantle ( Figure 33 ). The striae are parallel to weakly radiate in the middle, becoming slightly convergent near the apices and continue around the apical part of the mantle ( Figures 31 and 33 ). The areolae are 55 in 10 μm. Areolae openings are square near the axial area, becoming

slightly elongated towards valve margins ( Figure 33 ). Internally, the axial area is linear and straight slightly raised over valve plane ( Figure 30 ). The stauros is narrow and bow tie-shaped, raised on a wider rectangular hyaline fascia ( Figure 30 ). The raphe is straight, the central endings are weakly bent to the same direction and terminate on a shallow helictoglossae ( Figure 30 ). The distal endings are straight and terminate on a very shallow helictoglossae ( Figure 32 ). The cribrate areolae are rounded and slightly decreasing in size towards valve margin ( Figure 34 ). Cribra are composed of four, very rarely 5–7, peripheral pores and a single central one. The pore openings are almost similar in size ( Figure 34 ). On the cingular bands there are several rows of elongated and rounded areolae ( Figure 36 ).

Ecology: Craspedostauros cf. laevissimus was found in a brackish water habitat, epiphytic on the brown macrophyte Desmarestia sp. , constituted 1.8 % of the diatom assemblages on this host. Water temperature at time of material collection was 12.3 ° C and salinity 4.9 psu. Several other diatom taxa associated with C. lateralis including Diatoma moniliforme (Kützing) C. Agardh (23 %), Diatoma tenuis C. Agardh (16.5 %), Tabularia fasciculata (12 %), Gomphonema sp. (5.3 %), Rhoicosphenia abbreviata (C. Agardh) Lange-Bertalot (5.1 %), Cocconeis sp. (4.1 %), Achnanthidium sp. (1.9 %), beside other very small Nitzschia spp. and Navicula spp. which constituted less than 2 %. Several macrophytes as well as benthic samples were collected from the study area and the surrounding region but C. lateralis was only found on Desmarestia sp.

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 28–36: Scanning electron micrographs of Craspedostauros cf.laevissimus. (28) Internal side of two valves with different outline and size. (29) External side of the valve exhibiting weakly inflated central part and a slight undulation of valve face. (30) Valve interior showing the stauros occupying the middle part of the central area, and the simple elongated proximal raphe endings. (31) External central area with the elongated proximal raphe endings. (32) Internal valve pole showing raphe distal ending and striae spreading around all valve apex. (33) External valve pole with the curved raphe distal ending. (34) Rounded areolae with cribral pores, note the equal size pf peripheral and central pores. (35) Frustule in girdle view. (36) Enlarged part of the frustule showing a cingular band with numerous longitudinal rows of variable sized elongated areolae. Scale bars: (28, 29, 35) 10 μm; (30, 31, 32, 33, 36) 2 μm; (34) 1 μm.