Meridion humerosum 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 : 26-27

Meridion humerosum Neplyukhina & Chudaev sp. nov.

Description:— LM ( Figs 30–41 ): Frustules in girdle view narrowly cuneate with distinctly stepped headpole (only paired cells observed, which may be results of preceding cell division, as well as colony fragments). Valves heteropolar, narrowly wedge-shaped, length 19.0–43.5 µm, width 5.4–7.1 µm (n=18). Headpole capitate to rostrate, clearly set off the rest of valve by distinct shoulders. Footpole protracted, capitate. Sternum very thin, filiform. Striae parallel, irregularly spaced due to presence of transapical ribs devoid of ornamentation. Striae density 15.9–22.0 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 present through whole valve length. Rib density 3.1–5.1 in 10 µm. One rimoportula remoted from headpole, located beneath the “neck” of capitate headpole, adjacent to sternum.

SEM, external valve surface ( Figs 49–51 ): Valve face flat. Striae composed of circular areolae, occluded externally. Areolae density 52–61 in 10 µm. Areola occlusions in very shallow depressions. Apical pore fields, composed of smaller unoccluded pores present at headpole mantle, and probably at footpole mantle too, but the latter is not fully clear from taken micrographs. Rimoportula opening slit-like, transapically oriented, adjacent to sternum, terminates a stria, displaced proximally from headpole. Spines completely absent.

SEM, internal valve surface ( Fig. 52 ): Striae composed of circular pinhole-like unoccluded areolae. Transapical ribs present through the whole valve length, ribs elevated above internal valve surface. Rimoportula slit transapically oriented, positioned between distinct lips.

SEM, cingulum structure ( Fig. 52 ): Only a fragment of valvocopula was observed from internal surface. It bears one row of evenly spaced perforations together with one fragmented perforation row. No evidence of presence of septum at the headpole.

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. 32 , isotype: LE A0002282 ) .

Etymology: —The specific epithet reflects that valves of the species always have distinct shoulders beneath the headpole (lat. humerus —shoulder).

Distribution and ecology:— Species so far found only in the type locality with relative abundance less than 1%. For associated taxa see M. tenuipes section.

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 49–52. Meridion humerosum sp. nov., SEM, type material. 49–51. External valve surface. 50. Headpole of the valve depicted in Fig. 49. 52. Internal valve surface and part of valvocopula. Scale bars = 5 µm (49, 51, 52), 1 µm (50).