Meridion tenuipes Neplyukhina & Chudaev, 2023

Neplyukhina, Alisa & Chudaev, Dmitry, 2023, Two new species of the diatom genus Meridion (Bacillariophyta, Tabellariaceae) from Aleutian Islands, Phytotaxa 587 (1), pp. 21-30 : 22-26

Meridion tenuipes Neplyukhina & Chudaev sp. nov.

Description:— LM ( Figs 4–29 ): Frustules narrowly cuneate in girdle view, mainly single (paired cells observed occasionally, interpreted as post-division cells, or fragments of colonies). Valves heteropolar, narrowly clavate, length 22.5–64.0 µm, width 3.3–4.7 µm (n=38). Headpole capitate (some small valves at end of size reduction without constriction). Footpole gradually narrowing to very thin subcapitate apex. Sternum very thin, filiform. Striae parallel, irregularly spaced due to presence of transapical ribs devoid of ornamentation. Striae density 15.7–21.4 in 10 µm. Areolae not discernible in LM. Transapical ribs from both sides of sternum mainly fused in centre, forming complex ribs, going transversely or obliquely from mantle to mantle. Ribs absent in the lower third of valve. Rib density 3.1–5.2 in 10 µm. One rimoportula located close to headpole margin, adjacent to sternum.

SEM, external valve surface ( Figs 43, 46–48 ): Valve face flat. Striae composed of circular areolae, occluded externally.Areolae density 57–71 in 10 µm.Areola occlusions in very shallow depressions.Apical pore field, composed of smaller unoccluded pores presents at footpole. Rimoportula opening slit-like, transapically oriented, adjacent to sternum, terminates a stria in close proximity to headpole. Small conical spinules of irregular size positioned on virgae (1–2 per virga) at valve face-mantle junction. Small plaques present at mantle edge.

SEM, internal valve surface ( Figs 44–45 ): Striae composed of circular unoccluded areolae. Transapical ribs present in upper two thirds of valve, ribs elevated above internal valve surface, increasing in height and width towards mantle. Rimoportula slit transapically oriented, positioned between distinct lips.

SEM, cingulum structure ( Figs 42, 45 ): Cingulum composed of 4–5 open bands, decreasing in width towards abvalvar edge. Pars exterior with one row of regularly spaced perforations, adjacent to pars interior. Additional irregular rows present at head part of valvocopula and wider advalvar copulae, disappearing towards footpole. The most abvalvar narrow copula without such additional rows. Valvocopula with a small but distinct septum at headpole. Perforations on copulae occluded externally.

Type: — USA. Alaska: Aleutian Islands, Unalaska Island, puddle near Pyramid Creek Road , bottom sediment, 53°50’03.3”N 166°33’11.1”W, A. B . Savinetsky , 06 June 2018 (Holotype: MW-D! slide # 1099s1 = Fig. 6 , isotype: LE A0002281 ) .

Etymology: —The specific epithet reflects the characteristic very narrow footpole (lat. tenuis —narrow, pes — foot).

Distribution and ecology:— Species so far found only in its type locality. Its relative abundance is 1%. Associated taxa: Aulacoseira spp. (19%), Odontidium mesodon ( Kützing 1844: 47) Kützing (1849: 12) (12.5%), Tabellaria flocculosa ( Roth 1797: 192) Kützing (1844: 127) (10.5%), Eunotia spp. (5%), Diatoma tenuis C. Agardh (1812: 15) (4.5%), Staurosira venter ( Ehrenberg 1854: 13) Cleve & J.D.Möller (1879: no. 242) (4.5%), Achnanthidium spp. (4%), Rossithidium nodosum ( Cleve 1900: 13) Aboal (2003: 178) (4%) and other genera (less than 4% each).

Figures

FIGURES 4–41. 4–29. Meridion tenuipes sp. nov., LM, type material, slide MW-D 1099s1, Fig. 6 represents the holotype. 30–41. Meridion humerosum sp. nov., LM, type material, slide MW-D 1099s1, Fig. 32 represents the holotype. 4–20, 31–41. Valve views. 21–30. Girdle views. Scale bar = 10 µm.

FIGURES 42–48. Meridion teniupes sp. nov., SEM, type material. 42. Whole frustule in girdle view. 43. External valve surface. 44. Internal valve surface. 45. Internal valve surface and valvocopula. 46–47. External surface of the headpole. 48. External surface of the footpole. Scale bars = 5 µm (42–45), 1 µm (46–48).