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with 1% toluidine blue in 1% borax and fast dried, again on a hot plate. Sections were observed under an optical microscope for cell structure, before being examined at higher magnifications in a transmitted electron microscope.

3.4.2.3 Transmitted Electron Microscopy (TEM) and High Voltage Electron Microscopy

(HVEM)

Ultra-thin (0.50 nm) sections, required for TEM, were cut using a diamond knife. Gromiids have silica grains within their tests and therefore it was difficult to obtain good sections. Semi- thin sections (50 µm) were also cut using a diamond knife. These were examined in the HVEM (Figure 5.2.15), which physically accommodates and visualizes sections up to 1 mm thick. All cut sections were stretched using chloroform and placed on either TEM or HVEM grids that were dried before staining with uranyl acetate for use in either microscope.

3.3

A taxonomic survey of gromiids from the Arabian Sea

Supergroup Rhizaria

Order Gromida Claparède and Lachman, 1859 Suborder Gromiina Delage and Héouard, 1986 Family Gromiidae Reuss, 1862

Genus Gromia Dujardin, 1835

Gromia sphaerica Gooday, Bowser, Bett and Smith 2000(Figure 3.11)

Described by Gooday et al. (2000)

Occurrence: Oman margin CD 143 stations: 55759#1 (1100 m), 55744#1 (1200 m), 55767#1 (1390 m), 55789#3 (2030 m), 55726#1 (2075 m). Pakistan margin CD 145 stations: 55841#1 (1620 m), 55737#1 (1791 m) and 55815#1 (1799 m). Pakistan margin CD 151 station: 56137#12 (1852 m).

Description. Test typically spherical. Five specimens found on megacores were 12 to 20 mm diameter (average 15 mm, S.D. 5). The organic wall is thin, flexible and transparent, covered with multiple apertures of 0.02 mm average diameter. Oman and Pakistan specimens of Gromia

sphaerica are visually the same, with the slight difference that in the Pakistan specimens the test

contents fill the test while in the Oman specimens, the test contents are looser and do not fill the entire test interior.

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Gromia sp.1 – grape-shaped (Figures 3.12 and 3.20 A)

Occurrence: Oman margin CD 143 stations: 55717#1 (1341 m), 55767#1 (1390 m), 55731#1 (1414 m), 55710#1 (1422 m), 55774#2 (1684 m), 55752#1 (1692 m), 55730#2 (1980 m), 55775#1 (1990 m), 55725#2 (2010 m), 55789#3 (2030 m), 55726#1 (2075 m).

Description:

Light microscope observations. A grape-shaped morphospecies with a thin translucent organic

test wall, often with a pinkish reflective stain resembling mother of pearl on one side; test contents often not filling the whole test. The test is broadly oval in outline with smoothly rounded ends and gently curved sides; based on 104 specimens measured, dimensions are as follows: length 0.6 to 5 mm (average 2 mm, S.D. 0.5), width 0.6 to 2.8 mm (average 1.3 mm, S.D. 0.3). Test filled with brownish stercomata and loose sediment-like material. Oral capsule prominent, ranging from 0.06 to 0.3 mm diameter (average 0.1 mm, S.D. 0.03).

HVEM observations. Gromia sp.1 (Figure 3.20 A) has a thin outer test, with pores running

through it, underlain by a single or multiple honeycomb membranes. This species looks like the classical ultrastructure photographs of Gromia oviformis wall structure (Hedley and Bertaud 1962).

Gromia sp.2 – grape-shaped (Figures 3.13 and 2.20 B)

Occurrence: Oman margin CD 143 stations: 55717#1 (1341 m), 55767#1 (1390 m), 55731#1 (1414 m), 55710#1 (1422 m), 55774#2 (1684 m), 55752#1 (1692 m), 55725#2 (1980 m), 55730#2 (1980 m), 55775#1 (1990 m).

Description:

Light microscope observations.Morphospecies with droplet-shaped test, oval in general shape

but with an evenly rounded aboral end and a more narrowly rounded oral end; based on 110 specimens measured, dimensions are as follows: length 0.6 to 3.4 mm (average 1.7 mm, S.D. 0.6), width 0.5 to 2.8 mm (average 1.4 mm, S.D. 0.5). Very distinctive wall, which has a honeycomb-like structure visible under a binocular microscope. This is not to be confused with the honeycomb membranes only visible in the HVEM. Test filled with brownish stercomata and loose sediment-like material. Oral capsule prominent, ranging from 0.02 to 0.4 mm width (average 0.2 mm, S.D. 0.07).

HVEM observations. The rather peculiar honeycomb-like structure of the test wall can be seen

very clearly on the HVEM micrographs (Figure 3.20 B). It appears to represent the outer test layer present in other gromiids and is quite rigid. The structure appears to comprise at least 2 layers of polygons. The outer layer is open, so that the outer edges of the walls of the polygon project into the surrounding medium. The walls of the polygon are penetrated by a series of open spaces, which in places beaks the walls up into kind of lattice-like structure. These do not appears to be the same as the pores observed in other species. The outer honeycomb layer is underlain typical honeycomb membranes, arranged in layers parallel to the test.

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Gromia sp.3 – sausage-shaped (Figures 3.14 and 3.21)

Occurrence: Oman margin CD 143 stations: 55717#1 (1341 m), 55731#1 (1414 m), 55710#1 (1422 m), 55730#2 (1980 m), 55775#1 (1990 m). Pakistan margin CD 145 stations: 55841#1 (1620 m), 55737#1 (1791 m) and 55815#1 (1799 m). Pakistan margin CD 145 station: 55910#3 (1875 m).

Description:

Light microscope observations. A very elongate gromiid with a sausage-shaped test and a thin

translucent organic wall. The test has smooth rounded ends and parallel sides; based on 17 specimens measured, dimensions are as follows: length 1.4 to 11.4 mm (average 6.8 mm, S.D. 4.8), width 0.3 to 4.5 mm (average 1.4 mm, S.D. 0.8). Length:Width ratio = 4.8. Test filled with brownish stercomata and loose sediment-like material. Oral capsule prominent, ranging from 0.04 to 0.4 mm width (average 0.4 mm, S.D 0.6).

HVEM observations. It was difficult to obtain good sections for this large morphotype and

therefore no HVEM images were obtained. DIC photographs taken by Sam Bowser show that the wall of Gromia sp.3 is covered in pores, inlaid by a layer of stercomata, mainly concentrated at the proximal end of the test (Figure 3.21). The oral capsule is clearly illustrated in Figure 3.21.

Gromia sp.4 – spherical (Figure 3.15)

Occurrence: Oman margin CD 143 stations: 55753#1 (1093 m), 55717#1 (1341 m), 55767#1 (1390 m), 55731#1 (1414 m). Pakistan margin CD 145 stations: 55811#1 (1174 m), 55802#7 (1200 m), 55802#4 (1201 m), 55841#1 (1620 m), 55737#1 (1791 m), 55815#1 (1799 m), 55826#2 (1833 m), 55827#4 (1867 m), 55827#3 (1870 m) and 55830#2 (1874 m). Pakistan margin CD 151 stations: 56139#2 (1193 m) and 56140#2 (1859 m).

Description. Test typically spherical, 0.8 to 5.0 mm diameter (average 2.6 mm, S.D. 1.1) with a single aperture of 0.08 to 0.05 mm diameter (average 0.2 mm, S.D. 1); measured from 16 specimens. Oral capsule relatively small compared with other species. The organic wall is thicker and more flexible than in Gromia sphaerica. When dropped on the floor this gromiid type bounces like a tennis ball.

Gromia sp.5 – grape-shaped (Figure 3.16)

Occurrence: Oman margin CD 143 station: 55725#2 (2010 m) and Pakistan margin CD 151 stations: 56137#2 (1852 m) and 55910#3 (1875 m).

Description. This morphospecies is based mainly on molecular data rather than morphological data. It is a grape-shaped morphospecies with either a thin, translucent test wall or a thick, opaque test wall, sometimes with a pinkish reflective stain resembling mother of pearl on one side. The test is broadly oval in outline with an evenly rectangular shape, smoothly rounded ends and gently curved sides. However, there are slight variations in test shape which span the

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