Longinata acuta Hajós

Williams, David M. & Sims, Pat A., 2023, The diatom genus Longinata Hajós (Bacillariophyta): structure, relationships and distribution, Phytotaxa 591 (3), pp. 209-219 : 210-213

Longinata acuta Hajós in Hajós & Stradner 1975: 935, pl. 13, fig. 12 (= Figure 5 ) emend D.M.Williams & P.A.Sims

Holotype:— NEW ZEALAND, Campbell Plateau, South Pacific ( Hajós & Stradner 1975: fig. 1), “ DSDP Leg 29, Sample 275-1-2, 40-42 cm […] Upper Cretaceous” ( Hajós & Stradner 1975: 935), holotype = BP 2800/1! = Hajós & Stradner 1975: pl. 13, fig. 12, = reproduced as our Figure 5 and specimens in Figures 1, 2 )

Localities:—Upper Cretaceous: DSDP Leg 29, see Table 1 below; DSDP 275 1-2, 123-4, our Figures 7, 8, 11 , 12, 13 .

Valves thin, taper from centre towards poles, width 7–10μm at centre, ≤ 2μm at poles, length 80–120μm ( Figs 1–5 , 15 ). No visible sternum, mantle shallow at centre, larger at poles where valve becomes raised into extended protrusion at each pole (ca. 2–2.5μm) ( Figs 4, 5, 8–17 ). Base of polar protrusion with pore-field composed of closer packed and regular ‘puncta’ (areola) ( Figs 8, 11 , 14 , 18 ). Internally, pore-field extends along valve margin by ca. 5–10μm ( Figs 9 , 18 ). Valve surface smooth with small, irregularly placed ‘puncta’ (areola), internally simple holes, externally with rim and slightly raised from surface ( Figs 12–17 ). Faint outline of ‘rib-like’ structure at valve centre ( Figs 1–2 ), sometimes absent ( Figs 3–5 , 15–17 ): internally absence of any structure ( Figs 3–5 , 12, 13 , 15–17 ), externally ‘riblike’ structure as small ‘pegs’ extending outwards meeting similar at adjacent valve ( Fig. 10 , arrows, Fig. 12 , dashed arrow, Fig. 16 , Fig. 17 , double-headed arrow, Fig. 18 , three parallel arrows); occasional smaller pegs either side of larger protrusions, limited to centre of valve ( Fig. 12 , arrows, Fig. 17 , double-headed arrow). Towards poles, valve raised as single protrusion at each pole ( Figs 8, 11 , 14 ). Base of protrusion with pore-field composed of closer packed and regular ‘puncta’ (areola) ( Figs 8 , 14 , 18 ), tip plain ( Figs 11 , 18 ). Internally, pore-field extends along valve margin by ca. 5–10μm ( Fig. 9 ). Rimportulae possibly present ( Fig. 12 , arrow), internally sometimes on mantle ( Figs 16, 17 , single-headed arrows).

Although just the one figure was provided by Hajós, the recorded stratigraphic range indicated its occurrence elsewhere in the same core ( Table 1 ). Examination of the Hajós slides kept in the Hungarian Natural History Museum (BP) yielded very few specimens, but all very much with the same appearance as the holotype illustration (e.g., Figs 3, 4 ). Since its first description by Hajós, Longinata acuta has been rarely encountered, with the only additional report in Chambers (1997: 291, pl. 13, fig. 35); his specimens are here interpreted as Longinata fueloepi .

Figures

FIGURES 1–11: Longinata acuta Figs 1, 2, LM holotype BP 2800/1!, New Zealand, Campbell Plateau, South Pacific, “DSDP Leg 29, Sample 275–1-2, 40-42 cm […] Upper Cretaceous”, specimen length = 90μm, width = 5μm (at widest point); Figs 3, 4, BP 2800/1!, Fig. 5, L. acuta reproduced from Hajós & Stradner 1975: pl. 13, fig. 12; Figs 6, 7, Longinata fueloepi, “DSDP Leg 29, Sample 275-1-2, 130-132 cm […] Upper Cretaceous” (Hajós & Stradner 1975: 935), Fig. 6, SEM of while valve, internal view, scale bar = 20μm, Fig. 7, reproduced from Hajós & Stradner 1975, pl. 13, fig. 19; Figs 8–11, SEM, Fig. 8, detail of poles, Fig. 9, internal view of pole showing ‘pore-field’-like structure, two arrows, Fig. 10, external view of surface of valve with ‘pegs’ arrowed; Fig. 11, external view of pole showing ‘pore-field’-like structure, arrow. Scale bars = 20μm (Figs 1–4, 6), = 2μm (Fig. 8), = 5μm (Figs 9–11, 13, 14)

FIGURES 12–14: Longinata acuta SEM, Fig. 12, pair of valves with ‘peg’ arrowed, shorter projections with plain arrow, adjoining pegs with hashed arrows; Fig. 13, external view with scattered pores on surface, rimoportula arrowed; Fig. 14, paired valves at poles, ‘pore-field’-like structure, arrowed. Scale bars = 5μm.

FIGURES 15–18: Longinata acuta SEM, Fig. 15, pair of whole valves; Fig. 16, detail from specimen in Fig. 15, showing rimoportula (arrow) and sparse poroids; Fig. 17, detail showing rimoportula (arrow) and ‘pegs’ (double-headed arrow). Scale bars = 20μm (Fig. 15), 5μm (Fig. 16, 18), 2μm (Fig. 17).