Achnanthes apiculata (Greville) 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 : 111-112

Achnanthes apiculata (Greville) comb. nov. ( Figs 1 , 58–61 , Table 2)

Basionym: Stauroneis apiculata Greville, Edinburgh New Philosophical Journal, New Series 10: 30, pl. 4, fig. 8. 1859 (figure reproduced here as Fig. 1 ).

Description: —From David M. Williams’s photographs ( Williams 1988: 47, pl. 54, figs 2, 3), it can be stated that it has an elliptic-apiculate shape, 12.5–13.0 striae in 10 μm, with an extended but thin stauros clearly present. Individual length 45 μm. These images do not permit to determine if the taxon is a biraphid as supposed by R.K. Greville. Our type examination ( Figs 58–61 ) shows that it is a monoraphid diatom, even if the RV striation is difficult to focus on ( Figs 60, 61 ). The stauros extends to the half of the valve width. The SV striae, slightly radiate and present at the apices ( Fig. 59 , arrow), are composed of rectangular-oblong areolae, the SV sternum is narrow ( Fig. 58 ).

Type:— UNITED STATES. California, Patos guano (slide BM 1753, cf. Williams 1988). Figs 58–61 .

Remarks:—Since Achnanthes apicultat a (R.M. Patrick 1945: 167, pl. 1, figs 4–5) R.A. Matthews (1982: 193) is an invalid name, it cannot prevent the use of this name for a new combination. Stauroneis apiculata is cited by P.T. Cleve as a synonym of Achnanthes mammalis (Castracane) Cleve (1895) . See the discussion in Mann (1925). Stidolph et al. (2012: pl. 22, fig. 22) illustrate an individual (with both valves and apparently uniseriate striae) as Cocconeis apiculata , with a RV stauros and no shoulders near apices, stating that ‘this species will be transferred to the genus Schizostauron Grunow (1867: 28) ’ (A. Witkowski in litt. 2012).

Achnanthes mammalis (Castracane) Cleve (1895: 187 , pl. 3, figs 13–15) ( Figs 7–9 , Table 2)

Basionym: Rhaphoneis mammalis Castracane (1886: 48 , pl. 26, fig. 3, upper valve reproduced here as Fig. 6 ).

Homotypic synonyms: Actinoneis mammalis (Castracane) Cleve (1895: 187) , Cocconeis mammalis (Castracane) F.W. Mills (1933: 426 , 435), Nematoplata mammalis (Castracane) Kuntze (1898: 146) ( Fourtanier & Kociolek 2009, 2011).

Type:—THAITI. Challenger material from the harbor of Tahiti, not found in BM.

Remarks:—Among P.T. Cleve’s figures 13–15 (1895: pl. 3), the SV illustrated in figs 14, 15 (reproduced here as Figs 8, 9 ) can be attributed to Raphoneis mammalis , but with a detail absent in the original description: the presence of a double row of small puncta per stria ( Fig. 9 ). The fig. 14 (reproduced here as Fig. 7 ) illustrates a RV that may be identified either as Stauroneis thaitiana or as Stauroneis apiculata ( Fig. 1 ), seeming very close to each other. Unfortunately, no Castracane slide housed in BM is labelled as Stauroneis thaitiana . Concerning Stauroneis (?) obesa Greville , the type examination by Williams (1988: 47, pl. 54, figs 5, 6) and our own observations (see below) definitively establish its belonging to the Achnanthales , with particular characters (see below).

According to Foged (1978: 28, pl. 13, fig. 6 reproduced here as Fig. 10 with permission of E. Schweizerbart), Fig. 10 would illustrate Achnanthes mammalis var. reticulata with apparently a double row of puncta per stria, and without the reticulate aspect shown in the original illustration of Achnanthes mammalis var. reticulata Cleve (1895: 187 , pl. 3, fig. 16, reproduced here as Fig. 11 ). Furthermore, the smooth lemon shape (without shoulders) of the valve illustrated by Foged (1978) would be closer to Achnanthes mammalis var. mammalis than to Achnanthes mammalis var. reticulata .

In slide BM 2887 (R.K. Greville’s collection), an individual with biseriate SV striae ( Figs 62–64 ) and lemon-shaped valves (without shoulders) may be close to Achnanthes mammalis . This taxon has a butterfly-shaped large RV stauros ( Fig. 64 ) permitting to differentiate it from Achnanthes meisteri Hustedt in Schmidt et al. (1937: pl. 415, figs 19, 20). Note that BM 2887 is labelled as Stauroneis obesa but modern microscopy permits to resolve the unique biseriate structure of the SV striae ( Figs 62, 63 ).

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 58–67. 58–61. Achnanthes apiculata comb. nov. 62–64. Achnanthes cf. mammalis. 65–67. Achnanthes obesa comb. nov. 58. Individual from BM 1753, note the SV oblong rectangular areolae (arrow) and the position of the underlying RV extended and narrow stauros (arrowheads). 59. Apical areolae (arrow). 60. Laciniate marginal striae around the stauros (arrows). 60, 61. RV strongly radiate striae (arrowheads). 62, 63. Individual from BM 2887 with biseriate SV striae (arrowheads). 62. Apices free of areolae. 64. RV striae strongly radiate, stauros extended and high, reaching half valve width. 65, 66. Individual from BM 2593. 67. Individual from BM 2736, note the lateral gibbosities. 65. SV rectangular areolae. 66. RV striae strongly bent on apices (arrowhead). 67. Butterfly RV stauros (arrowheads) and striae radiate and thin (arrow). Scale bars = 10 μm.