Craspedostauros confusus Zidarova, M.de Haan, P.Ivanov, Hineva & Van de Vijver, 2022

Zidarova, Ralitsa, Haan, Myriam De, Ivanov, Plamen, Hineva, Elitsa & Vijver, Bart Van De, 2022, The genus Craspedostauros E. J. Cox (Bacillariophyta) on the coasts of Livingston Island, Maritime Antarctica, Phytotaxa 572 (1), pp. 1-24 : 12

Craspedostauros confusus Zidarova, M.de Haan, P.Ivanov, Hineva & Van de Vijver sp. nov. ( Figs 9– 6 , 8, 8–56)

Description

LM observations ( Figs 9– 6 , 8 ):— Frustules lanceolate in girdle view with convex, rarely weakly constricted (and hence biarcuate) margins, bearing numerous copulae. Longer valves linear with broadly rounded apices ( Fig. 19 ), becoming narrowly lanceolate to elliptic-lanceolate in smaller valves with more cuneately rounded ( Figs 21, 22 ), sometimes almost subrostrate apices ( Fig. 23 ). Valve margins weakly convex ( Fig. 21 ) to almost straight in the middle ( Figs 20, 22, 24 ), lacking any constriction. Valve dimensions (n = 16): length 22.0–49.5 µm, width 4.5–6.5 µm. [Valves (n = 27) observed in other populations on Livingston Island during the study ( Figs 60–77, 79 ) had a valve length of 18–50 µm and a valve width of 4.0–6.5 µm]. Axial area very narrow, linear ( Figs 19–24, 28 ). Central area narrow, forming an almost rectangular ( Fig. 19 ) to bow-tie-shaped fascia ( Figs 20–24, 28 ), widening towards the valve margins. Raphe filiform, straight ( Fig. 19 ) to weakly undulating, with expanded central raphe endings, and elongated terminal raphe fissures, unilaterally weakly bent ( Figs 21, 24, 28 ). Striae rather coarse, parallel to occasionally very weakly radiate in the middle ( Fig. 22 ), parallel to very weakly convergent near the apices ( Figs 19, 24 ), 22–24 in 10 µm. Areolae, at least the larger ones bordering the axial area, weakly discernible in LM ( Fig. 19 ).

SEM observations ( Figs 8–56 ):— Valve face weakly domed, with a deep mantle ( Figs 48–51 ). External raphe branches straight with weakly undulating ( Fig. 49 ) to straight ( Fig. 51 ) central raphe endings, terminating in drop-like expanded pores ( Figs 49, 51 ). Terminal raphe fissures continuing shortly onto the mantle, unilaterally hooked ( Figs 48, 51 ). Axial area triangularly expanded at the apices, bearing a silica flap on one side, covering the terminal raphe fissures ( Fig. 50 ). Striae uniseriate, composed of cribrate, rounded to elliptic areolae. Near the raphe areolae clearly larger ( Figs 49, 50 and Figs 88–90 ). Cribrum structure of the areolae bordering the axial area possessing four to seven peripheral pores, and two to three central pores. All other areolae with cribra composed of 2–5 peripheral pores, lacking central pores ( Figs 49, 50 ). Areolae continuing around the apices ( Figs 48, 50 ), ca. 25–30 in 10 µm. Internal areolar openings rounded to elliptic ( Figs 53–56 ). Internal raphe straight, located on a distinct sternum ( Figs 52, 53 ). Central raphe endings terminating onto double helictoglossae ( Figs 53, 55 ). Terminal raphe endings finish onto broad helictoglossae. Stauros narrow, located on a wider hyaline fascia ( Figs 52, 53, 55 ).

Type:— ANTARCTICA. South Shetland Islands: Livingston Island , Hannah Point , sample 14 (62° 39’13” S, 60° 36’ 41” W), marine epilithon, R. Zidarova, 16th December 2018 (holotype BR-4760 ! = Fig. 28 , isotype Slide 417! (University of Antwerp, Belgium)) .

Etymology:— The species epithet, confusus, Latin for confusing, reflects the complex taxonomic history of the genus Craspedostauros in the Antarctic Region, and the possible long-term inclusion of this species within the more common Antarctic species C. laevissimus .

Ecology and associated diatom flora:— Craspedostauros confusus sp. nov. was found as abundant in the epilithon of several tidal pools at Hannah Point (sample 14, type), Mongolian (Reserve) Port (samples DNA5 and MO’), and Caleta Argentina (sample LT6). The salinity level in the pools (when measured) ranged between 33 and 35 PSU (Table 1), and their diatom flora was dominated by various species, including Navicula spp. , Melosira spp. , Parlibellus sp. , Tabulariopsis australis ( Peragallo 1921: 67) D.M. Williams (1988: 249) and Tripterion margaritae ( Frenguelli & Orlando 1958: 98) L.F. Fernandes & Sar (2009: 67) .

Figures

FIGURES 9–. SEM images of Craspedostauros laevissimus (sample 11). 29. External valve view.30.Close up of the central area of the same valve showing the expanded central raphe endings and cribrate areolae.31. Close up of the apex of the same valve showing the bent and expanded distal raphe endings and a cribrate areola with two central pores (white arrow). Note the presence of areolae and pores around the raphe endings on the apex (black arrows).32. External valve view.33. Same valve, close up of the central area with the expanded and slightly curved central raphe endings.Arrow shows a cribrate areola with three central pores. 34. Same valve, close up of the apex with white arrows showing the presence of both areolae with and without central pores. Note also the presence of areolae and pores on the apex (black arrows). Scale bars = 5 μm (Figs 29, 32); 1 μm (Figs 30, 31, 33–34).

FIGURES 5 –56. SEM images of Craspedostauros confusus sp. nov. from the type population (sample 14). 52. Internal valve view. 53. Close up of the central area internally, showing the narrow stauros on a wider hyaline area, the central raphe endings with double helictoglossa and the rounded to elliptic internal areolar openings. Arrow shows an areola with seven central pores, visible internally. 54. Close up of the apex with the pores of cribrate areolae internally (arrows). 55. Close up of the central area of another valve of the same population, showing once again the narrow stauros, the internal central raphe endings with double helictoglossa and rounded internal areolar openings. 56. Close up of the apex with rounded to elliptic and even somewhat irregular in shape internal areolar openings. Scale bars = 5 μm (Fig. 52); 1 μm (Figs 53–56).

FIGURES – 8.LM images of Craspedostauros laevissimusand C.confusus sp.nov. 2–8.Craspedostauros laevissimus (sample 11).9–18. Craspedostauros laevissimus (sample 13). 19–26. Craspedostauros confusus sp. nov. (type population, sample 14). 27. Craspedostauros laevissimus (enlarged view of Fig. 4, sample 11). 28. Craspedostauros confusus sp. nov. (enlarged view of Fig. 22, type specimen). Scale bars = 10 µm.

FIGURES – 7. SEM images of Craspedostauros laevissimus from different populations. 42. Close up of the central area externally, showing the weakly expanded central raphe endings and the cribrate areolae with usually four to five peripheral pores and up to one central pore (sample 13). 43. Close up of the central area internally, showing the narrow stauros located in a wider hyaline area, the central raphe endings with double helictoglossa, and the rounded to rectangular areolar openings internally (sample 13). 44. Close up of the apex, showing the bent distal raphe endings, cribrate areoale with up to six peripheral pores and up to two central pores (sample 13). 45. Close ups of both the valve exterior and interior (sample 11), showing the weakly expanded central raphe endings externally; the areolae near the raphe with usually four to five peripheral pores and one central pore; the central raphe endings with double helictoglossa and the rounded areolar openings internally. 46. Internal valve view, showing the narrow transverse rib of silica at the valve center (strauros) and the central raphe endings with double helictoglossa (sample 11). 47. Close up of the apex of the same valve internally, showing the rounded to square or rectangular areolar openings (sample 11). Scale bars = 5 μm (Fig. 46); 1 μm (Figs 42–45,47).

FIGURES 60–85. LM images of Craspedostauros confusus sp. nov. and C. laevissimus from several populations from Livingston Island. 60–67. Craspedostauros confusus sp. nov. (sample DNA5). 68–77. Craspedostauros confusus sp. nov. (sample LT6). 78–79. Craspedostauros confusus sp.nov. (sample MO’), Fig.78 showing afrustule withnumerous copulaein girdleview.80–84.Craspedostauros laevissimus (sample LT10). 85. Craspedostauros laevissimus (sample 13). Scale bar = 10 µm.

FIGURES 86–90. SEM images of Craspedostauros confusus sp. nov. and C. laevissimus from several populations from Livingston Island. 86. External valve view of Craspedostauros laevissimus (sample LT10). 87. Close up of the striae of the same valve, showing the occasionally present enlarged areolae near the raphe, without central pores (arrow). Note the density of areolae in comparison to Fig. 88 below. 88–90. Close ups of the central area (Fig. 88) and apices (Figs 88–90) of Craspedostauros confusus sp. nov. (sample MO’), showing the typically enlarged cribrate areolae near the raphe, usually with several central pores. Scale bars = 5 μm (Fig. 86); 1 μm (Figs 87–90).