Septuma, TENDAL & HESSLER, 1977

Gooday, Andrew J., Kamenskaya, Olga E. & Cedhagen, Tomas, 2007, New and little-known Komokiacea (Foraminifera) from the bathyal and abyssal Weddell Sea and adjacent areas, Zoological Journal of the Linnean Society 151 (2), pp. 219-251 : 224-234

GENUS SEPTUMA TENDAL & HESSLER, 1977

Type species: Septuma ocotillo Tendal & Hessler, 1977

SEPTUMA OCOTILLO TENDAL & HESSLER, 1977

( FIGS 3 , 4 )

Septuma ocotillo Tendal & Hessler, 1977, p. 180 , textfig. 4; pl. 9, fig. C; pl. 10, fig. A–B; pl. 12, fig. A–B; pl. 19, fig. A; pl. 20, fig. A–F; pl. 21, fig. A–D

Septuma ocotilla Tendal & Hessler. Schröder, Medioli & Scott, 1989, pp. 33–34 ; pl. 2, fig. 5; pl. 8, fig. 1; text-fig. 12

Septuma ocotillo Tendal & Hessler. Kamenskaya, 1993, p. 78 , fig. 2

Septuma ocotillo Tendal & Hessler. Kamenskaya, 1996, p. 220

Diagnosis:Test bush-like, consisting of tubules of essentially even diameter that usually radiate from central region; early stages involve narrow branches arising alternately from both sides of axial tubule. Length:width ratio of tubules very variable, but consistently> 10 and sometimes> 20. Tubules fairly flexible, branching more or less sparsely, dichotomously, divided internally by septa that are pierced by foramina. Single long, thin-walled, non-septate tubule sometimes developed. (Modified after Tendal & Hessler, 1977.)

Holotype: Argo H-30, central North Pacific , epibenthic sledge sample: 30°05′N, 156°12′W; 6065–6079 m water depth. Zoological Museum, Copenhagen; preserved in alcohol.

ANDEEP material: Stn 59#5, 3 specimens; Stn 59#7, 1 specimen; Stn 59#11, 9 specimens; Stn 81#9, 3 specimens; Stn 88#4+5 combined, 10 specimens; Stn 88#5, 1 specimen; Stn 88#7, 14 specimens; Stn 88#8, 156 specimens; Stn 88#9, 1 specimen; Stn 94#7, 1 specimen; Stn 94#11, 13 specimens; Stn 94#14, 21 specimens; Stn 102#8, 11 specimens; Stn 102#10, 6 specimens; Stn 102#13, 54 specimens; Stn 110#6, 2 specimens; Stn 110#8, 66 specimens.

Description of holotype

The holotype measures 2.40 mm in maximum dimension (2.90 mm including two rather longer tubules) and consists of numerous tubules of varying lengths, many of them gently curved ( Fig. 3A, C ). The longer tubules have a length/width ratio> 20, the shorter ones have a length/width ratio of <20. They are generally 50–65 µm in diameter, decreasing to 35–50 µm near the thin-walled extremities, and branch 2–3 times. Branching is most common near the base of the tubules; the longer tubules have long, unbranched distal sections. Closely spaced septa are visible in some tubules, particularly towards their extremities ( Fig. 3B ). The tubules arise from a central area consisting of 3–4, short, wide branches, 85–125 µm in width, which divide into a number of main branches, ∼80 µm in width ( Fig. 3D ).

Description of ANDEEP material

Specimens that appear complete are rounded in overall shape and are slightly to strongly flattened. ‘Bushy’ specimens range from 1.7 to 3.1 mm (typically ∼ 2.5 mm) long, 1.3–3.0 mm (typically 2.2 mm) wide and 1.0– 2.4 mm (typically ∼ 1.4 mm) thick. The largest spidery variants (see below) reach maximum dimensions of> 4 mm. The ANDEEP material reveals the following previously undescribed features.

1. Two general types of test can be distinguished ( Fig. 4A ). (i) Relatively compact, bushy tests composed of fairly broad (60–80 µm, up to 100 µm in the central part of the test) tubules with fairly thick, semi-opaque, finely agglutinated walls and length/ width ratios generally <15 ( Fig. 4B ). (ii) Rather untidy, ‘spidery’ tests consisting of tubules with long branching intervals and thinner, often semi-transparent walls. Centrally, the tubules may be fairly broad but they rapidly become narrower (30–50 µm) away from the centre. The length/width ratio of the tubules often exceeds 20. These two variants cannot be separated consistently. Both kinds of tubule are sometimes found within one specimen.

2. Part of the test is sometimes organized around a more or less linear tubule that gives rise to regularly spaced side tubules, arising alternately on either side of the test ( Fig. 4D, E ). The tubules are usually the thinner, semi-transparent type and may represent the earliest part of the test. Thicker tubules may be arranged in a similar manner in the central part of the test. Compact, bushy tests usually do not exhibit this feature.

3. A single, unbranched, thin-walled, non-septate tubule, usually longer than other tubules, arises from the central part of the test in some specimens ( Fig. 4F ). This tubule may also represent the initial part of the test.

4. The number of septa is quite variable, even within a single individual. They tend to be numerous and easily visible in the narrow, semi-transparent tubules ( Fig. 4C ) but sparsely developed in the wider, more opaque tubules.

Remarks

This is one of the most common komokiaceans in ANDEEP samples. The holotype (possibly the specimen illustrated by Tendal & Hessler, 1977: p. 9, fig. C) is generally similar to the ‘spidery’ ANDEEP morphotype, although it has more branches than most specimens and the central tubules are distinctly thicker.

To some extent, the wide range of morphologies represented in the ANDEEP material of Septuma ocotillo is mirrored in published illustrations of this species. The ‘spidery’ morphotypes are similar to pl. 10 of Tendal & Hessler (1977) as well as Schröder et al. (1989: pl. 8, fig. 1). The ‘bushy’ morphotypes resemble the illustrations of Schröder et al. (1989: text-fig. 12) and Kamenskaya (1993: fig. 2). One of Tendal & Hessler’s SEM photographs (1977, pl. 10, fig. B therein) appears to show the axial tubule with lateral branches observed in some of our specimens, although the view of this feature is not clear.

Distribution

First described from the abyssal Central North Pacific ( Tendal & Hessler, 1977), subsequently from ∼ 5770 m water depth on the Nares Abyssal Plain, north-west Atlantic ( Schröder et al., 1989) and at two stations in the Cape Basin (2790 and 4912 m) ( Kamenskaya, 1993). Its occurrence at the ‘Komsomolets’ wreck site in the Barent Sea (73°44′N, 13°16′E, 1700 m depth) provides the most northerly record ( Kamenskaya, 1996). In our material, S. ocotillo is common in the eastern and central Weddell Sea (4526–4934 m).

SEPTUMA BRACHYRAMOSA KAMENSKAYA, 1993

( FIG. 5A–G )

Septuma brachyramosa Kamenskaya, 1993, p. 78 , fig. 3

Septuma sp. Gooday, 1990 , pl. 2, fig. B

Septuma sp. Gooday, 1994 , fig. 1g

Diagnosis: Test fairly compact, bush-like, composed of relatively short tubules that branch dichotomously 2–3 times and have a length/width ratio of around 10. Septa thin but clearly developed. Long, non-septate tubule occasionally present.

Material: Stn 16#11, 1 specimen; Stn 57#2, 4 specimens; Stn 78#9, 4 specimens; Stn 80#9, 2 specimens; Stn 81#9, 3 specimens; Stn 121#7, 3 specimens and several fragments.

Description

The 17 specimens range in maximum dimension from 1.1 to 2.4 mm. The test is compact, bush-like and pale brown or tan in colour ( Fig. 5A, B ). The dark contents can only be seen faintly through the wall when specimens are examined in water. In a few cases, the inner region of the test is obscured by sediment ( Fig. 5D ). The test comprises relatively short, branched, more or less cylindrical tubules of generally even diameter (60–100 µm, typically 80 µm), sometimes narrowing slightly towards the tips and with rounded ends. Where the tubules are visible to their full extent, they typically branch dichotomously 2–3 times and have a length/width ratio of ∼10. The tubules follow a relatively even course and are not crooked. Some specimens have a long, non-septate tubule that extends up to more than 2 mm from the main part of the test ( Fig. 5F ).

The test wall is composed of fine-grained material and has a fairly smooth surface except for scattered larger mineral grains ( Fig. 5C, E, G ). These are mainly clear quartz but also include black, green and brown particles, usually up to 70–80 µm, sometimes 150 µm (e.g. Stn 81#9) in size. Where these grains are more numerous (e.g. Stn 121#7), the branches have a rather knobbly appearance. Radiolarian and occasionally planktonic foraminiferan tests may also be incorporated into the walls of the tubules. One small individual is attached to a large Cyclammina test. The wall is typically 6–15 µm thick, sometimes thinning to 3–4 µm at the tips where the agglutinated layer is weakly developed or even absent ( Fig. 5G ). In specimens from Stn 81#9, however, the wall is distinctly thicker (13–25 µm) and there is no obvious thinning at the tips of branches. The tubule interiors are divided by very thin septa ( Fig. 5C, E, G ). These are usually fairly numerous but are more sparsely developed in specimens from Stn 121#7. The sections of the tubules between the septa are largely filled with numerous small, oval stercomata, 6.5–13 µm in maximum dimension.

Remarks

The single example in the ANDEEP collection of Septuma brachyramosa from the Cape Basin (Stn 16) is very similar to the type and other specimens of Kamenskaya (1993), which originated from the same area. However, a few specimens from the Weddell Sea (e.g. Stn 57) have a long, unbranched, non-septate tubule (pl. 5, fig. G), a feature not observed in the original material.

In our samples, S. brachyramosa is distinguished from S. ocotillo mainly by its more compact shape and the shorter, relatively wider tubules that have a length/width ratio of around 10. We have recently examined an extensive collection of Septuma material from the Porcupine Abyssal Plain (north-east Atlantic) in which ocotillo- like morphotypes and more compact, brachyramosa- like morphotypes are linked by intermediate forms. We suspect therefore that these two types may represent a single, morphologically variable species. However, until this problem can be studied further, we prefer to treat them as separate species.

Distribution: First described from the Cape Basin (4910 m water depth) and also present in our material from Stn 16 in the same area (4694–4730 m). We report it for the first time from the eastern Weddell Sea, off Neumayer Base and Cap Norvegica (1812– 4420 m), and the north-west Weddell Sea near the tip of the Antarctic Peninsula (2616–2620 m). There are additional records from the north-east Atlantic Porcupine Abyssal Plain (4841 m) ( Gooday, 1994) and the Madeira Abyssal Plain (6059 m) ( Gooday, 1990).

SEPTUMA KOMOKIFORMIS KAMENSKAYA, 1993

( FIG. 6 )

Septuma komokiformis Kamenskaya, 1993, pp. 78–79 , fig. 4.

Diagnosis: Test bush-like, composed of long, crooked, in some cases flattened tubules, branching 2–3, sometimes four times, usually dichotomously but sometimes trichotomously. Number of branches and degree of ‘bushiness’ vary. Many tubules terminate in fairly long, unbranched sections. Test may agglutinate scattered larger grains. Length:width ratio of tubules typically 15–20 but may exceed 20. Septa numerous.

Material: Stn 80#9, 24 specimens; Stn 80#5, 1 specimen; Stn 81#7, 1 specimen; Stn 81#8, 1 specimen; Stn 81#9, 2 specimens.

Description

The 29 specimens range in size from 1.6 to 3.8 mm. The test is bush-like ( Fig. 6A–C ), light greyish in colour, consisting of long crooked tubules which branch 2–3, sometimes four times, in most cases dichotomously but on occasions trichotomously. The width of the tubules tends to decrease from 80 µm near the base to 40–60 µm in the periphery; some narrower tubules have a more consistent diameter (50– 60 µm) along their length.

The number of branches and the corresponding degree of ‘bushiness’ vary considerably. A specimen (2.4 × 1.6 mm) from Stn 81#8 has only seven main branches, which are crooked, especially in the distal part, up to 1.4 mm long, with length/width ratios of ∼20–22. A bushier specimen (2.4 × 2.2 mm) from Stn 81#7 has more than 20 branches, about 1.2 mm long, with length/width ratios in the range 15–20. Three specimens from Stn 80#9 (2.4 × 2.2, 2.2 × 2.1, 1.8 × 2.6 mm) have 7–12 long, crooked branching tubules ( Fig. 6D ). Another 17 specimens from the same sample range in size from 3.8 × 3.2 to 2.0 × 1.8 mm. They are bushier with more than 30 closely spaced tubules in the largest individual ( Fig. 6A–C ). The tubules are long, crooked and sometimes flattened with length/width ratios of ∼15–20; fairly long, unbranched sections are developed at the ends of many tubules.

The organic base of the tubule wall is overlain by a layer of fine agglutinated particles that create a smooth surface finish. The wall is well defined and rather even in width (6–10 µm) ( Fig. 6E ). Agglutinated particles may be largely absent near the tips of the branches, leaving the organic layer exposed. All specimens also incorporate scattered larger particles, mainly clear quartz and dark mineral grains. These vary widely from small particles ∼40 µm in size to large grains up to several hundreds of micrometres in diameter. Specimens from Stn 80 are adorned with an attractive combination of white planktonic foraminiferan tests, dark mineral grains and clear quartz grains. The tubules are divided by numerous septa ( Fig. 6E ) and the chambers between the septa are filled with small (6–10 µm) stercomata.

Remarks

Specimens of Septuma komokiformis from the Weddell Sea, particularly those from Stn 80#9, are very close to the type material from the flanks of the Valdivia Seamount. They have similar overall dimensions, long, crooked, sometimes flattened branches, and incorporate large agglutinated particles. The crooked branches and unbranched distal parts of many tubules distinguish this species from S. ocotillo and S. brachyramosa .

Distribution

First described from the flanks of the Valdivia Seamount (1758 m) and also found in the Angola Basin (2370–4770 m) ( Kamenskaya, 1993). Ours is the first report of this species from the Weddell Sea, where it occurs at depths of 3103–4526 m.

SEPTUMA STELLATA SP. NOV.

( FIGS 7–9 )

Diagnosis: Test compact, relatively small (up to 1.6 mm in diameter), consisting of tubules radiating out from central region that is usually obscured by sediment. Most tubules fairly stiff, branching dichotomously, somewhat irregular in width (30–50 µm), crooked and often with bead- or knob-like lateral swellings and protuberances, sometimes extending into short side branches. Length: width ratio of tubules typically 10–15. Septa fairly numerous. Few narrower, more or less straight, parallel-sided tubules, devoid of septa, extend for variable distance beyond the main tubules.

Type material and locality: The holotype and three paratypes were collected from Stn 94#11 using an Agassiz Trawl ; 66°38.05′S, 27°5.90′W to 66°38.10′S, 27°5.46′W; 4894–4995 m water depth. They are preserved in 4% buffered formalin and deposited in the ForschungsInstitut Senckenberg, Frankfurt am Main, under reg. nos. SMF XXVII 7529 (holotype) and SMF XXVII 7530 (three paratypes) .

Other material examined. Stn 88#4+5 (combined), 6 specimens; Stn 88#7, 1 specimen; Stn 88#8, 6 specimens; Stn 102#13, 4 specimens; Stn 110#8, 5 specimens; 121#7, 2 specimens; 142#5, 2 specimens; Stn 142#7, 1 specimen.

Derivation of name: Latin stella = star; alluding to the star-like, radiating arrangement of the test branches.

Description of type specimens.

The holotype and three paratypes are generally similar ( Figs 7 , 8C ). The test is 1.10–1.60 mm in diameter (0.76–1.55 mm discounting the occasional longer tubules) and occupies a more or less spherical or somewhat flattened space. It consists of fairly stiff tubules that radiate outwards. The inner region from which the tubules arise is usually obscured by a dense mass of sediment. Occasionally, the sediment is lacking and the tubules are seen to originate from the core of densely packed tubules in which it is difficult to discern the branching pattern.

There are usually two kinds of tubules ( Fig. 8C ). The majority are relatively short, more or less crooked and somewhat irregular in width (30–50 µm). Because the centre of the test is usually obscured, the length/ width ratio of the tubules is difficult to estimate, but assuming that they originate in the central region, it is typically 8–15. The tubules usually give rise to bead- or knob-like lateral swellings and protuberances, sometimes extending into short side branches ( Fig. 8D ). They branch dichotomously, occasionally trichotomously. The walls are 3–5 µm thick and consist of an organic layer overlain by a layer of small mineral grains. Scattered across the surface of the wall are some much larger mineral grains, several hundreds of micrometres in size, usually quartz but also some dark grains. A minority of tubules are narrower, more or less straight, parallel sided and tapering from 30– 35 µm to 15–18 µm in width at their distal ends. Some of these narrower tubules can be traced into the inner part of the test but most of them develop as extensions of the main tubules. They often extend out for a variable distance beyond the main tubules; the longer ones have a length/width ratio of 15–20. The wall is thinner (1–2 µm thick) than that of the main tubules and predominantly organic with few agglutinated particles.

The crooked, wider tubules have obvious transverse septa, <1 µm wide and generally spaced 15–35 µm apart. The interior of these tubules is partly filled with small, oval stercomata, 6–10 µm in diameter. The longer, narrower tubules are devoid of septa and typically empty.

Other ANDEEP material

Specimens from other samples are generally similar to the types ( Figs 8A, B, F, G , 9 ). Diameters range from 0.86 to 1.23 mm without the longer tubules and up to 1.60 mm including them. The longer tubules are well developed in some specimens (Stns 94#11, 102#13, 142#5) but are not always present. The core region of the test is usually, but not always, obscured by sediment. In one specimen from Stn 110, the wall of the tubules is overlain by a layer of flocculent material, resulting in a fuzzy appearance.

Remarks

We place this distinctive species in Septuma based on the presence of radiating tubules with clearly developed septa. It is distinguished from other Septuma species by the relatively small size of the test, the development in most specimens of a sediment core that obscures the central region of the test, and the presence in many specimens of parallel-sided, non-septate extensions to some tubules. Longer, non-septate tubules are sometimes found in S. brachyramosa and S. ocotillo but individuals of these species never have more than one such tubule. Unlike other Septuma species in which the tubules are approximately parallel-sided, the main tubules in S. stellata give rise to lateral swellings that impart a rather crooked, knobbly appearance.

Distribution: This new species is most common on the Weddell Abyssal Plain (4696–4934 m). A few specimens occur at shallower depths off the north-west peninsula slope (2603 m) and in the Powell Basin (3406 m).

Figures

Figure 3. Septuma ocotillo Tendal & Hessler, 1977, holotype, Zoological Museum, Copenhagen. A, general view with focus on upper tubules; B, outer tubules with septa; C, general view with focus on central tubules; D, detail of wide central tubules.

Figure 4. Septuma ocotillo Tendal & Hessler, 1977. A, Stn 88#8, two compact morphotypes and two ‘spidery’ morphotypes; B, Stn 88#8, compact morphotype; C, Stn 88#8, specimen viewed with transmitted light showing closely spaced septa; D, Stn 59#11, specimen with central tubule giving rise to lateral tubules. E, Stn 88#8, specimen with central tubule giving rise to lateral tubules. F, Stn 102#8, specimens with long, unbranched, non-septate tubule.

Figure 5. Septuma brachyramosa Kamenskaya, 1993. A, Stn 78#9, general view, transmitted light; B, Stn 16#11, general view, reflected light; C, same specimen, detail of tubule with septum (arrowed); D, Stn 78#9, upper two specimens without sediment between tubules, lower two specimens with sediment filling between tubules; E, Stn 78#9, detail of tubule with septa (arrowed); F, Stn 52#7, general view of specimen with long, non-septate tubule; G, same specimen, detail of tubule with septum (arrowed).

Figure 6. Septuma komokiformis Kamenskaya, 1993. Specimens from Stn 80#9, photographed in water. A–D, complete specimens; E, detail of tubule with septa (arrowed), photographed in glycerol.

Figure 7. Septuma stellata sp. nov., type specimens from Stn 94#11, photographed in water. A, holotype, reg. no. SMF XXVII 7529, reflected light; B, same specimen, transmitted light; C, paratype, reflected light; D, same specimen, transmitted light; E, second paratype, reflected light; F, same specimen, transmitted light. Both paratypes are registered under SMF XXVII 7530.

Figure 8. Septuma stellata sp. nov. Specimens photographed in glycerol, transmitted light. A, Stn 102#13, general view; B, detail of longer, straight, non-septate tubule and adjacent crooked tubule; C, Stn 94#11, paratype, general view; D, detail showing crooked tubules; E, Stn 102#13, general view of specimen which lacks long tubules; F, Stn 88#8, general view of specimen with relatively long crooked tubules; G, same specimen, detail of crooked tubule with lateral swellings. Paratype registered under SMF XXVII 7530.

Figure 9. Septuma stellata sp. nov., specimen from Stn 88#8 photographed in glycerol. A, general view, transmitted light; B, detail showing crooked tubules; C, dark-field illumination; D, detail showing end of tubule with lateral swellings; E, F, details of tubules with septa.