Leptammina grisea

Leptammina grisea gen. et sp. nov.

(Figs 1–2)

Material: Polarstern Station 102#11 (Agassiz trawl) 25 specimens; Station 102#13 (Epibenthic sledge) 2 specimens; Station 110#8 (Epibenthic sledge) 1 specimen; Station 133#2 (Epibenthic sledge) 1 specimen.

Derivation of name: grisea is the Medieval Latinization of the French word gris, and means grey. It refers to the colour of the test.

Diagnosis. Approximately spherical species of Leptammina, up to 2 mm diameter, characterized by soft, delicate, finely agglutinated test, grayish or violet-grey in colour and opaque, with dull, non-reflective surface. Single, prominent circular aperture. Cell body dark greenish, with single nucleus. Peduncular sheath well developed.

Deposition of type material: The holotype from Station 102#11 and paratypes from Stations 102#11, 102#13, 110#8, and 133#2 are deposited in the Forschungsinstitut Senckenberg, Frankfurt am Main, Germany, under reg. no. SMF XXVII 7537.

Description. General morphology. The test is free and a distinctive grey or violet-grey colour. Unfixed specimens are roughly spherical, occasionally more elongate, and often somewhat irregular in shape (Figs 1 A–D). The diameter ranges from 620 to 1360 µm (mean 0.91 mm; median 0.91 mm; n=24 individuals). There is one round aperture on a short neck and surrounded by a thin raised collar.

Test wall. The wall is soft, delicate and easily detached. The surface has a dull, non-reflective appearance. It is smooth when viewed under the light microscope but slightly rough when viewed at higher magnifications (1,000X–5,000X) in the SEM. The wall includes a thin, outer agglutinated layer, up to 30 µm thick, and an inner organic lining, ~3 µm thick (Figs 1 E–F; 2F). The outer layer is composed of small mineral particles varying in size from ~10 µm maximum dimension to 1 µm or less (Figs 2 A–B). Many of these particles are angular in shape.

Cell body. In fresh, newly collected individuals, the cell body is a dark green or brownish green and entirely fills the test (Fig. 1 E–F). A distinct peduncular sheath (stomostyle) is located immediately inside the aperture and may extend into the apertural neck and cover the rim of the aperture (Fig. 2 C). It is also continuous with the inner organic lining of the test wall. Light microscopic sections reveal one large nucleus, up to 240 µm diameter, of the granular type with numerous nucleoli, located within an exonuclear vacuole. The center of the nucleus is occupied by a vacuole, up to 200 µm wide (Fig. 2 F). Large vacuoles are also visible within the cytoplasm of sectioned individuals. Pseudopodia were not observed, although a thin string of cytoplasm projects along the central axis of the peduncular sheath (Fig. 2 C). However, in critical-point dried individuals studied by SEM, the cell body consists of a dense network of fine pseudopodia (reticulopodia) that incorporate stercomata, mineral particles, diatoms, and other foreign particles (Fig. 2 D).

Remarks: Leptammina grisea gen. et sp. nov. closely resembles Saccammina alba in the general form and construction of the test. The main differences are that the test is larger (620 to 1360 µm compared to a maximum size of 400 µm in S. alba), the test wall is thicker, and the surface is greyish rather than white. It should also be noted that S. alba was described from an intertidal setting whereas the new species occurs at bathyal and abyssal depths. Leptammina grisea gen. et sp. nov. differs from Pilulina argentea in having a dull grey rather than reflective, silvery surface. See also “Remarks” under L. flavofusca gen. et sp. nov.

Distribution: Weddell Sea, central part at 4795, 4822, and 4698 m depth, northwestern part at 1580 m depth.