Achnanthes trachyderma (F.Meister) Riaux-Gobin & Compère & Hinz & Ector, 2015

Riaux-Gobin, Catherine, Compère, Pierre, Hinz, Friedel & Ector, Luc, 2015, Achnanthes citronella, A. trachyderma comb. nov. (Bacillariophyta) and allied taxa pertaining to the same morphological group, Phytotaxa 227 (2), pp. 101-119 : 108

Achnanthes trachyderma (F.Meister) comb. nov. ( Figs 19, 20 , 27–29 , Table 2)

Basionym: Cocconeis trachyderma F.Meister, Berichte der Schweizerischen Botanischen Gesellschaft 44: 99, figs 63, 64. 1935 (figures reproduced here as Figs 19, 20 ).

Translation of the original diagnosis:—‘Valves elliptical with elongate, capitate endings, 29 to 32 μm long, 14 to 15 μm wide. Raphe valve with 26 radiate, punctuate-dotted striae and a stauroid central area, which extends beyond the midline of the half valve. Rapheless valve with a very narrow pseudoraphe and 9 to 11 coarsely punctate striae in 10 μm. Not rare in Nagasaki’.

Type: — JAPAN. Nagasaki, ‘shell of a marine snail from Nagasaki’, see Materials & Methods (lectotype here designated among the numerous slides from Nagasaki studied by Meister and containing this species: Z!, slide 3409008 in coll. F. Meister’s, illustrated here as Fig. 29 . See Table 1).

Type observation:— The taxon is rare in F. Meister’s and M. Voigt’s slides. The individuals are small (ca. 25.6 μm long, 13.2 μm wide; ca. 11.5 SV striae in 10 μm and 25.5 RV striae in 10 μm), relatively narrow (L/W: 1.94), with wellmarked shoulders near the apices. The RV stauros is wide-ranging and thin, reaching almost the margins ( Fig. 29 ). It can be remarked that the Nagasaki material also contains individuals slightly bigger (ca. 33.1 μm long, 17.4 μm large, 10.2 SV striae in 10 μm and 21.3 RV striae in 10 μm) but with an extended stauros as in the smaller individuals .

Remarks:—M. Voigt, in his hand notes about ‘ Cocconeis trachyderma v. elliptica Mfrd. Vgt. ’ (an undescribed variety marked from slide 22045, Nagasaki: ‘similar Meister’s type’) refers to ‘ Achnanthes ?’ as a remark, proving his doubts about its belonging to Cocconeis . Meister (1935: 99) also illustrated a SV of Cocconeis citronella from his Nagasaki material, with the remark that the latter has a lanceolate pseudoraphe, being narrow in Cocconeis trachyderma . Furthermore, Meister (1935: 99) specified that the central area is much shorter in Cocconeis citronella than in C. trachyderma .

Material from Society Archipelago (South Pacific): —(LM: n=3, Figs 30–32 ; SEM, n=21, Fig s 45–57 ). The individuals from the Society Archipelago are always small (25.6 + 2.9 μm long; 13.2 + 0.9 μm wide), the SV stria density is higher than in A. citronella ( Table 1) and the stauros is extended; the SV sternum is narrow. This taxon is frequent in Tahiti and Moorea Islands. The morphology of the South Pacific taxon ( Figs 30–32 ) roughly matches that of Achnanthes trachyderma comb. nov. The SEM examination allows to add some details to the diagnosis: the SV is strongly convex, one row of SV large areolae lies on each side of the narrow sternum ( Figs 45–47 ), the SV apices are void of areolae except in rare cases ( Fig. 46 , arrowhead), the valvocopula system lacks fimbriae ( Fig. 47 , arrowhead). The SV areolae hymenes are externally smooth (with no apparent perforations or slits, Fig. 49 ), and lying under the valve face ( Fig. 49 , arrow); in internal view they show a complex structure with a grid pattern ( Figs 48, 50, 51 ). The cingulum is composed of the valvocopulae and an additional copula (C in Fig. 49 ). The SV striae (11.5 + 0.7 striae in 10 μm) are parallel in mid-valve to only slightly radiate at the apices ( Fig. 50 ). The RV is slightly concave ( Fig. 52 ), finely striated (25.5 + 1 striae in 10 μm), with striae strongly radiate and composed of small areolae internally closed by domed hymenes ( Fig. 55 , arrowhead), with one row of longer areolae near the margin ( Fig. 52 , arrow). The raphe is filiform and straight, the axial area narrow, the central raphe endings straight and close to each other, the terminal raphe fissures very slightly undulating and continuing on the mantle ( Figs 56, 57 ). The central area is enlarged in a narrow but extended stauros delineated on the margins by short striae ( Fig. 53 , arrow; Fig. 54 , arrowheads). Helictoglossae are low ( Fig. 53 , arrowhead).

Figures

FIGURES 1–24.1. Stauroneis apiculata. 2, 3. Cocconeis apiculata. 4.Stauroneis(?) obesa. 5. Cocconeisrobusta. 6. Rhaphoneis mammalis. 7–9. Achnanthes mammalis. 10. Achnanthes mammalis var. reticulata according to Foged (see text, reproduced with permission of E. Schweizerbart). 11. Achnanthes (Actinoneis) mammalis var. reticulata. 12. Unnamed individual in Schmidt et al. (1895, pl. 198, fig. 40). 13, 14. Cocconeis citrina. 15–17. Cocconeis citronella. 18. Cocconeis sabangi. 19, 20. Cocconeis trachyderma. 21, 22. Achnanthes schmidtii. 23, 24 Achnanthes schmidtii (reproduced with permission of E. Schweizerbart). Scale bars = 20 μm.

FIGURES 25–32. 25, 26. Achnanthes citronella. Individuals from type slide 43609, labelled as ‘Jolo Jolo, Sulu, Philippine Islands, 3-17’ (see Fig. 34), A. Mann’s collection, housed in US. Lemon-shaped SV with an elliptic SV sternum (Fig. 25, arrowhead) and rectangular areolae without axial arrangement, RV finely striated, detached open valvocopula without fimbriae (Fig. 26, arrow) and a short butterflyshaped stauros. 27–32. Achnanthes trachyderma. 27–29. Individuals from Meister’s slides collection, housed in Z. Frustule from slide 3409001 showing a large RV stauros and fine RV striae (Fig. 27), and SV coarse striation (Fig. 28). 29. Illustration of the lectotype. A RV from slide 309008, with a fine striation and a narrow extended stauros. 30–32. Achnanthes trachyderma. Individuals from Society Archipelago, South Pacific, with relatively large stauros (Fig. 30, arrowheads), SV striae parallel, only slightly radiate at the apices, narrow sternum (Fig. 31). 32. RV with fine striae and large and thin stauros. Scale bars = 10 μm.

FIGURES 45–51. Achnanthes trachyderma. Individuals from Society Archipelago, SEM. 45. SV external side, with narrow sternum. 46. Apices with areolae (arrowhead). 47. Valvocopulae system lacking fimbriae (arrowhead). 48. SV internal side, with open SVVC (arrow) and no fimbriae (arrowheads). 50. Internal SV areolae pattern and no areolae on apices. 49. Detail of the cingulum composed of the two valvocopulae (SVVC and RVVC) and a supplementary copula (C). 51. Detail of the internal structure of the SV areolae. Scale bars = 5 μm (Figs 45–48, 50); 1 μm (Figs 49, 51).

FIGURES 52–57. Achnanthes trachyderma. Individuals from Society Archipelago, SEM. 52. RV external side with laciniate stauros reaching almost the margin. 53. RV internal side with the stauros marginally delineated by very short striae (arrow), low helictoglossa (arrowhead). 54. RV external side with large stauros (arrowheads). 55. Detail of the central area in internal side, with areola domed hymenes (arrowhead). 56. RV apex with strongly bent striae with a marginal row of larger areolae. 57. Terminal raphe fissure continuing on the mantle. Scale bars = 5 μm (Figs 52–54); 1 μm (Figs 55–57).