Bithekammina occulta

Silva, Ana Aranda Da, Gooday, Andrew J., Pearse, Richard B. & Cunha, Marina R., 2011, A new ‘ saccamminid’ genus (Rhizaria: Foraminifera), from 4400 m water depth in the Nazaré Canyon (NE Atlantic), Zootaxa 2912, pp. 49-58 : 51-56

Bithekammina occulta gen. et sp. nov.

Derivation of name. Occulta , derives from the Latin occultus, which means hidden, mysterious. In this case it refers to the fact that the inner ‘saccamminid’ is easily overlooked within its outer agglutinated casing.

Type material. The holotype (Pl.2 fig. A), from Station 56859# 2 in the Nazaré canyon, is deposited under reg. no. ZF5241. Paratype 1 (Pl. 2, fig. B) and paratype 2 (Pl. 2, fig. C,D), from the same station, are deposited under reg. nos ZF5242 and ZF5243, respectively. All of the type specimens originate from the 0.5–1.0 cm sediment layer.

Diagnosis. As for genus

Description. Test:

Morphology. The test is broadly oval to circular in outline, with a smoothly rounded proximal end and a circular cross section (Plate 1, figs A–D). The distal end is slightly flattened with a single aperture. This is a simple opening 25–30 µm diameter, with an indistinct, slightly raised rim and without any associated structures. Fine detritus typically accumulates around the aperture. Five specimens had the following dimensions: length 210–413 µm (mean 308± 88.6 µm), maximum width 210–370 (mean 279 ± 64.8 µm).

Wall structure and composition. The test wall is translucent and the rose-Bengal-stained cell body is clearly visible through it when the test is immersed in water and viewed in reflected light; it is more or less transparent in transmitted light (Plate 1, figs B, D). The surface is very smooth, unwrinkled, with a diffuse, silvery, reflective sheen (Plate 1, figs A, C). The wall is clearly defined and very thin (<5 µm), particularly at the proximal end, but slightly thicker (up to 15 µm) around the aperture. It is composed of several layers of very fine plate-like particles (1–5 µm, but usually 1–2 µm in size) that overlie an organic lining (Plate 1, figs E–H). X-ray microanalysis reveals strong peaks for Si and Al and smaller peaks for K, Ca, Mg, and Fe, consistent with a clay mineral composition ( Figure 1 ). When dried for SEM, the test wall crumples but still retains its integrity (Plate 1, fig. E).

PLATE 1. Bithekammina occulta gen. et sp. nov. A and B. Reflected and transmitted light photographs of specimen from Station 56859#2 core (4–5 cm layer). C–D Reflected and transmitted light photographs of specimen from Station 56859#2 core (0.5–1 cm layer). E–H. SEM images of the same specimen. E. Entire test, which crumpled when dried onto the stub. F–H. Details of agglutinated particles. Scale bars = 100 Μm except where indicated otherwise.

PLATE 2. Bithekammina occulta gen. et sp. nov., scale bars = 100 Μm. A. Transmitted light photograph from holotype, reg. no. ZF5241, from Station 56859#2 0.5–1 cm. B. Transmitted light photograph from paratype 1, reg. no. ZF5242, from Station 56859#2 0.5–1 cm. C and D. Transmitted light photograph from paratype 2, reg. no. ZF5241, from Station 56859#2 0.5–1 cm. E. Transmitted light photograph from specimens from Station 56859#2 1–1.5 cm.

PLATE 3. Bithekammina occulta gen. and sp. nov. SEM images of the outer case of specimen shown in Plate 1, figs C–H; Station 56859#2, 0.5–1 cm layer. B, C. Detail of the tubular extension showing organic lining. D. Surface of tubular extension. E, F. Details of main part of casing. Scale bars = 100 µm (A), 20 µm (B, E), 10 µm (D, F), 5 µm (C).

Test contents. The cell body is well defined and either fills the test cavity almost completely, or is separated from the wall by a narrow space, which is apparently empty (Plate 1, figs B, D). When viewed through the test wall, the cytoplasm appears dense and very finely granular with no obvious large inclusions such as stercomata. A large nucleus (~50-µm diameter) is visible in one specimen. An endosolenial tube is not clearly developed although a lighter area of cytoplasm immediately inside the aperture of one specimen when viewed in transmitted light suggests that such structure may be present.

Outer agglutinated case:

Morphology. In all available specimens, the test is contained within an outer agglutinated casing (secondary test) within which it lies fairly loosely (Plate 2). This structure is spherical to oval in shape. A narrow tubular extension, which is orientated on the same axis as the aperture of the inner test, is sometimes clearly developed. However, this structure is not always evident. When present, it presumably acts as a channel through which pseudopodia are deployed (Plate 2, fig. B) Eleven specimens had the following dimensions; length 364–770 µm (mean 496±117 µm), width 287–539 (mean 428±96 µm). The tubular extension ranged in length from 40 to 840 µm (shorter tubes were probably broken) with a width of 14 to 42 µm.

Wall composition and structure. The outer case is fragile, breaking easily when poked with a needle. It is composed mainly of irregularly-shaped grains, 10–50 µm in size (Plate 3, figs E,F), which yield X-ray spectra dominated by Si and are presumably composed of quartz ( Figure 2 ). Much smaller clay-sized particles are also present between the larger grains. The tubular extension is composed mainly of these smaller (<10 µm) grains (Plate 3, fig. A,B,D). An organic matrix partially obscures some of the grains on the outer surface, and what appears to be an organic lining is visible in SEM photographs of the tubular extension (Plate 3, fig. C).

Vertical distribution in the sediment. In three replicate cores (56847#6, 56847#7 and 56859#2), Bithekammina occulta was concentrated in the upper 3 cm of the sediment with only scattered specimens occurring at deeper sediment layers between 3 and 5 cm, the maximum depth sampled (Figure 3). The overall average living depth (ALD5) was 2.5. In addition to ‘live’ ‘saccamminids’, we also encountered empty outer cases. These were more abundant than the ‘live’ specimens and were found in deeper sediment layers (Figure 3). The average depth of occurrence of empty cases (ADDC5) was 4.6. All three replicate cores showed different numbers of ‘live’ and empty cases at each of the sediment layers, suggesting patchiness in the occurrence of this species.

FIGURE 3. Vertical distribution within the sediment profile (> 150 Μm) Bithekammina occulta gen. and sp. nov. from CD 179. A. ‘Live’ (stained) specimens, ALD5 = Average Living Depth. B. Dead (empty) cases, ADDC5 = Average Depth of Dead agglutinated cases.

Figures

FIGURE 1. X-ray microanalysis of the surface of the ‘ saccamminid’ test (specimen illustrated in Plate 1, figs C – H; 0.5 – 1.0 cm layer of the core from Station 56859 # 2).

FIGURE 2. X-ray microanalysis of a larger grain in the outer agglutinated case (specimen 1 illustrated in Plate 3, figs A – F; 0.5 – 1.0 cm layer of the core from Station 56859 # 2).