105

Wall structure and test morphology in three large deep-sea agglutinated foraminifera, Rhabdammina parabyssorum Stschedrina 1952, R. abyssorum

Sars 1869 and Astrorhiza granulosa (Brady 1879) (Foraminiferida, Textulariina)

ANDREW J. GOODAyl and CHRISTOPHER W. SMARr 1. Southampton Oceanography Centre, Empress Dock, European Way, Southampton, S014 3ZH, United Kingdom

2. Department of Geological Sciences, University of Plymouth, Drake Circus, Plymouth, PIA BAA, United Kingdom

ABSTRACT We describe novel test-wall features in two species, Rhabdammina parabyssorum from the Arabian Sea and Astroriziza granulosa from the NE Atlantic Ocean. These large agglutinated foraminifera have tests which consist of a central inflated region giving rise to a variable number of radiating arms. Both species include two- and three-rayed morphotypes and both have a two­layered wall structure in which a thin inner layer is overlain by a thicker, outer, friable layer. This wall structure has never been clearly described or illustrated before, despite the fact that one of the species, A. granulosa, has been known for well over a century. At least in R. parabyssorum, the outer layer is virtually devoid of cement while the inner layer contains well-developed 'undifferentiated' cement (sensu Bender, 1995). The well-known species Rhabdammina abyssorum differs from R. parabyssorum only in having a much simpler, unlayered wall structure. This raises questions about the taxonomic significance of wall structure versus test morphology in large agglutinated foraminifera. If these two forms are distinct species (the interpretation adopted here), then it indicates that morphologically identical sibling species exist among agglutinated foraminifera. The alternative interpretation, that these forms are variants of one species, implies that agglutinated wall structure may exhibit substantial intraspecific variability.

The function of the weakly cemented, friable outer test layer is not known. We offer the suggestion that in R. parabyssorum, it could possibly be a dynamic, ephemeral feature involved in some way with the trophic biology of the foraminifer.

INTRODUCTION Large agglutinated foraminifera are an important component of deep-sea biological communities, particularly in bathyal continental margins regions which receive a fairly substantial food supply (Gooday, 1990; Levin, 1991; Gooday et ai., 1997). Many of these taxa have fairly robust, albeit often brittle, tests and are easily collected, sometimes in large quantities, by dredges and other towed sampling gears. For this reason, they attracted the attention of pioneer deep-sea biologists such as W.B. Carpenter and M. and G.O. Sars and include some of the most familiar of deep-sea foraminifera.

One such species is Rhabdammina abyssorum which has a distinctive radiate, tubular test and has been recorded from a wide bathymetric range in many parts of the world. Much of the early material was collected using towed gears.

More recently, this species has been observed in life position in cores and has been the subject of some pioneering physiological observations (Linke, 1992). Here we describe a species, closely resembling R.

abyssorum, obtained in core samples from a 3400 m­deep site in the NW Arabian Sea, off the coast of Oman (Gooday et al., 1997). This form has a two­layered wall structure which is quite different from the relatively simple, single-layered wall typical of R. abyssorum, but very close to the description given by Stschedrina (1952b) of R. parabyssorum. The third species considered in this paper, Astrorhiza granulosa, occurs in epibenthic sledge material obtained by the Institute of Oceanographic Sciences (lOS, nowpart of SOc, the Southampton Oceanography Centre) on the continental slope off NW Africa.

We chose to examine Rhabdammina parabyssorum and A. granulosa because they both have an agglutinated wall consisting of two layers which differ in their composition, texture and degree of cementation. They also display a similar range of morphological variation. We describe these features and discuss their possible taxonomic and ecological significance.

In: Hart, M.B., Kaminski, M.A., & Smart, C.W. (eds) 2000. Proceedings of the Fifth International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 7, 105-115.

106 A.J. Gooday & C.W. Smart

Table 1. Positions of stations mentioned in text and figure captions.

Station and Date Lat. (ON) series numbers

Discovery 8973 4th Oct. '76 32° 1.9' Challenger 6th July '79 50° 10.4' 50606#1 Discovery 12719#1 1st Nov. '94 19° 07' Discovery 12671#3 11 th Oct. '94 19° 00.03' Discovery 12671#4 11 th Oct. '94 19° 00.29' Discovery 12687 18-20 Oct. '94 -19°

MATERIALS AND METHODS Station details are summarised in Table 1. The Rhabdammina parabyssorum sampling site on the Oman margin is situated below the Arabian Sea oxygen minimum zone and is characterised by bottom water oxygen concentrations around 3.0 ml.rl. Specimens of R. abyssorum were collected at this site in 1994 using an USNEL-type box corer, a Barnett­Watson multiple corer (Barnett et al., 1984), and an Agassiz trawl. They were picked from core surfaces or trawl catches and preserved immediately in 10% formalin buffered using sodium borate. Specimens of R. abyssorum from the Porcupine Seabight (NE Atlantic) and Astrorhiza granulosa from the NW African margin were collected in 1979 and 1976, respectively, using various versions of the lOS epibenthic sledge (Aldred et al., 1976). Residues from the sledge catches were fixed in buffered 10% formalin and later transferred to 80% alcohol for storage. Specimens were subsequently picked out from the >500 J1.m residue.

Light photographs were taken using a WILD M400 photomicroscope. For scanning electron micro­scopy, specimens were air dried, fixed to stubs using silver dag, coated with gold and examined either in a JEOL model 5300 or a JEOL model 6100 SEM at 20 or 25 Kv.

OBSERV A nONS

Rhabdammina parabyssorum Stschedrina, 1952

Plates 1 and 2 Rhabdammina parabyssorum Stschedrina 1952b, pp. 25-30,

pI. 1, figs 1-3.

The original description was based on material from the North Pacific (Bering and Okhotsk Seas). The new Arabian Sea record therefore extends the geographical range of this species considerably. Phenotypic variation. This species includes morpho­types which are radiate, tubular (biradiate) and branched (Le., with a single dichotomous fork). Out of 43 specimens individually picked from core sur­faces at Station 12687, 26 were three-rayed, 12 were two-rayed, 1 was one-rayed, 1 was five-rayed and 1 was branched. Three-rayed tests also dominated 277 more or less broken specimens from an Agassiz trawl

Long. Depth Gear (OW) (m)

11°19.4' 3003-3008 Epibenthic sledge 50° 40.1' 1110-1120 Epibenthic sledge

58° 39' 3000 Agassiz Trawl 59° 00.00' 3393 Multiple corer 59° 00.22' 3392 Vegematic box corer -59° -3350m Multiple and box cores

sample (12719#1) taken at the same site. More than 70% (194 specimens) were three-rayed, 27 (9.7%) were four-rayed, 3 (1.1%) were branched, 2 (0.72%) were five-rayed, and 2 (0.072%) were irregular in shape. The remaining 44 (15.9%) specimens, simple tubes longer than lcm, were regarded as two-rayed forms; this designation was somewhat arbitrary since some of these tubes could have been the broken arms of specimens with more than two arms. The branched morphotype resembles Rhabdammina major de Folin, 1887, a form considered by Gooday (1986) to be a variant of R. abyssorum on the basis of its identical wall structure. Wall structure. The test consists of an inner layer overlain, at least in places, by a variably developed outer layer (PI. I, Figs 1-3). Where the ends of the arms are undamaged, the inner layer may expand into a bell-shaped termination. The inner layer is composed of fairly well-cemented quartz particles and a variable proportion of sponge spicules, some of which protrude from its outer surface (PI. I, Figs I, 2, 6, 7). In some specimens it is composed almost entirely of spicules. On the inner surface of the test, the spicules lie flat within an organiC matrix to give a moderately smooth finish (PI. 2, Fig. 3), but otherwise they are not arranged in any particular pattern. Fractured test surfaces reveal the presence of organic cement which forms an extensive but rather featureless coating on spicules and other par­ticles (PI. 2, Figs 7,8). Places where particles have become detached are visible as rounded scars on cement covered surfaces. Strands and columns of cement are generally not developed.

The outer layer is more coarsely and loosely agglutinated (friable) than the inner layer. It has a somewhat irregular outer surface and is greyish­brown, in contrast to the lighter, more yellowish colour of the inner wall. It is generally thicker than the inner layer although the thickness varies con­siderably. The outer layer is best developed towards the centre of the radiate test and becomes discontin­uous towards the ends of the arms. Typically, the arms are characterised by wider sections where the outer layer is developed and narrower sections where it is missing and the inner layer of the wall exposed (PI. I, Figs 1-3). Sometimes, there is a rather abrupt step between these sections. In a few

Wall structure and morphology of three large tubular foraminifera 107

specimens, the outer layer is hardly developed on the radiating arms.

The outer layer is composed almost entirely of mineral grains, most of which appear to be quartz. The grains are subangular to sub rounded, a few lOs of microns to about 100 /lm in size, and jumbled together with no intervening matrix (PI. I, Figs 4,5). It there­fore incorporates an extensive system of intergrain voids (Pi. 2, Figs 5,6). Sponge spicules are generally absent but scattered spicules, juvenile globigeri­nacean tests, and small amounts of fine-grained material, are sometimes visible on undamaged outer surfaces. Very little cement is present; a careful examination of broken test surfaces revealed only very occasional, short columnar strands between adjacent grains.

Rltabdammina abyssorum M. Sars, 1869

Plate 3 Rhabdammina abyssorum M. Sars in Carpenter 1869 pp.

60-61. " , Rhabdammina discreta Brady, 1881, p. 48. Rhabdammina major de Folin, 1887, fig. 12a.

Phenotypic variation. Following Gooday (1986), Thies (1991) and Bender (1995), we regard Rhabdammina discreta and R. major as, respec­tively, two-rayed and branched morphotypes of R. abyssorum. Out of 373 specimens from the epibenthic sledge sample taken at Station 50606, 328 (87.9%) were three rayed, 36 (9.7%) were four rayed, 7 (1.9%) were two-rayed (i.e., tubes >lcm length); five-rayed and branched forms were each repre­sented by a single specimen (0.27%). Wall structure. The wall structure agrees well with the description given by Mendelson (1982) of speci­mens from the Scottish margin (NE Atlantic). It is relatively simple and homogenous without the inner and outer layers seen in R. parabyssorum (PI. 3, Figs 1-5). On fractured surfaces, the wall structure appears open with numerous irregular interconnect­ing voids (PI. 3, Fig. 6). It consists of large, sub­rounded to subangular quartz grains with the inter­stices filled by a jumble of much smaller, often somewhat angular particles. The large grains are generally 100-200 /lm in size, sometimes rather larger. Most matrix particles are <10 /lm and there are also some particles of intermediate size. Sponge spicules were not observed. The outer surface is dis­tinctly knobbly with many large, protruding quartz grains. Coccoliths are fairly numerous on the sur­faces between the large grains and form a kind of outer veneer (PI. 3, Fig. 5). Open voids are also exposed in these areas.

The wall is firmly cemented. The cement coats the grain surfaces (PI. 3, Fig. 7) and resembles that associated with the inner layer of Rhabdammina parabyssoru m.

Asfrorhiza granulosa (Brady, 1879)

Plate 4

Marsipella granulosa Brady, 1879, pp. 86-87, pI. 3, figs 8-9. Astrorhiza angulosa Brady, 1881, p. 48.

Phenotypic variation. Brady's two species have an identical wall structure and we agree with Jones (1994, p. 32) that they represent two- and three­rayed variants of one species (PI. 4, Figs 1,2). In our material from Station 8973, the two rayed form varies from tubular to cigar-shaped and the three­rayed form from triangular or sub triangular to more rounded or elongate in shape, typically with sides which are more or less curved. The two- and three­rayed forms each account for about half of the 47 specimens in this sample. Wall structure. The wall consists of distinct inner and outer layers of completely different composition (PI. 4, Figs 3, 5). The inner layer is yellowish­orange, thin and composed of fairly well cemented mineral grains of varying sizes. The outer layer is white, much thicker than the inner layer, loosely agglutinated, very friable and composed almost entirely of small juvenile globigerinacean tests (PI. 4, Figs 4,6,7). At the ends and comers of the test, the inner layer emerges to form a short projecting tube terminating in an aperture.

DISCUSSION Phenotypic variation in deep-sea foraminifera Phenotypic variation is well-known among shal­low-water foraminifera where it is associated with environmental variability, both natural and anthropogenic (Poag, 1978; Jorissen, 1987; Alve, 1995). In the deep sea, where conditions are gener­ally more uniform, such plasticity is less common, although many widely distributed calcareous species do show some degree of morphological vari­ability across their geographical and temporal ranges (Boltovskoy et al., 1991). Morphological variation is apparent among agglutinated taxa such as Reophax and some other hormosinaceans in which test morphology varies, sometimes consider­ably, according to the particles used in its construc­tion (Schroder, 1986). There is also obvious varia­tion in the number of tubular extensions (apertures) in species of Rhabdammina, Astrorhiza and Vanhoeffenella. All of these taxa contain more or less linear (biradiate) morphotypes, in addition to the more typical radiate forms. Both types are represented in R. parabyssorum, R. abyssorum and A. granulosa.

The number of rays developed in R. parabyssorum, R. abyssorum and A. granulosa is not obviously related to test size and may simply reflect random variation. A more interesting form of vari­ability seems to occur in Rhabdammina abyssorum. Gooday (1986) pOinted out that Rhabdammina major (=R. irregularis of some authors) has a wall struc­ture which is identical to that of R. abyssorum and R. discreta (now generally regarded as conspecific) and often co-occurs with these two forms. Stschedrina (1952a) also illustrated a branched

108 A.J. Gooday & C.W. Smart

Table 2. Some species of agglutinated foraminifera (and one xenophyophore) described as having a layered wall structure.

Species Test morphology Test structure Reference Astrorhiza Tubular, either Thin, friable outer layer, This study granulosa straight or radiate thinner, more strongly

cemented inner layer BathysipllOn Tubular, no proloculus Very thin outer veneer of Gooday & Claugher capillare plate-like particles (1989) B. major Tubular, no proloculus Thin, loose, outer layer of Gooday et al. (1995b)

black apatite particles B. rufescens Tubular, no proloculus Very thin outer veneer of Gooday & Claugher

plate-like particles (1989) B. rufus Tubular, no proloculus Very thin outer veneer of Gooday & Claugher

plate-like particles (1989) Critlzionina Irregular sphere, no Wall composed of fine siliceous Gooday et al. delacai aperture particles lined by a single (1995a)

layer of /Lm-sized grains bound by an organic sheet

C. granum Irregular sphere, no Wall composed of siliceous Hoglund (1947) aperture particles lined by a thin,

finely-grained, chalky-white inner layer

Pelosina Tubular with Wall composed of mud but Cartwright (1988) arborescens branched distal part with a thin inner layer of

quartz grains Pilulina argentea Spherical with Thin outer layer of minute, Hoglund (1947)

aperture flat-lying plate-like particles; inner layer of small rod-like particles embedded in a fine matrix

Rhabdammina Tubular, either Thin, friable outer layer, This study parabyssorum straight or radiate thinner, more strongly

cemented inner layer Occultammina Tubular, occasionally Outer layer mainly clay Tendal et al., (1981) profunda branching particles; inner layer of silt-(xenophyophore) sized mineral grains and

radiolarian fragments

morphotype among her specimens of R. abyssorum from various Arctic regions and the NE Pacific. The R. major form, in which the test branches dichoto­mously rather than being radiate, is represented in the Arabian Sea material of R. parabyssomm, albeit by only a few individuals. The significance of the branched R. major form is unclear, but it could possibly represent a stage in the life-cycle of these species.

constituent particles (Table 2). The layering often takes the form of a thin outer veneer which provides a smooth finish to the wall (e.g., a number of Bathysiphon species, Pilulina argentea), or a thin agglutinated lining to the test lumen (e.g., Crithionina delacai, C. granum, Pelosina arborescens). The tubular test of the xenophyophore Occultammina profunda has a 15-30 /Lm thick outer layer composed of fine clay particles and 50-90 /Lm thick inner layer composed of silt-sized mineral grains and radiolarian fragments (Tendal et al., 1981). Less well-defined test wall heterogeneity is encountered in other agglutinated foraminifera (Lindenberg & Auras, 1984, p. 98).

Wall structures in agglutinated foraminifera Layered walls. In many morphologically simple agglutinated foraminifera, the test wall is either one grain thick, or more than one grain thick with the grains arranged homogeneously throughout the wall (Hofker, 1972; Bender, 1995). Some species, however, have heterogeneous walls consisting of two clearly defined agglutinated layers which differ in the composition and/or arrangement of the

Our observations indicate that a distinctive kind of wall layering is developed in Rhabdammina parabyssorum and Astrorlziza angulosa. In both cases there is a friable outer layer (variably developed in R. parabyssorum) overlying a thinner

Wall structure and morphology of three large tubular foraminifera 109

but more firmly cemented inner layer. This structure is most similar to that of Pelosina arborescens, as described by Cartwright (1988), and completely dif­ferent from the thin surface veneer of particles which occur in some Bathysiphon species. Published accounts of A. angulosa, while not specifically describing the wall structure, do suggest that the inner and outer layers are a consistent feature of this species; the exposure of the inner layer at the test extremities is suggested by Brady's (1884, pI. 20, figs 10-22) illustrations and by Cushman's (1918, p. 11) description. Examination of Brady's original mate­rial in the Challenger collection (Natural History Museum, London) confirms that the test is two layered. The outer layer present in our material of Rhabdammina parabyssorum compares well with Stschedrina's (1952b) original description.

Cement microstructures. Bender (Bender & Hemleben, 1988; Bender, 1989, 1995) described the nature and morphology of organic and calcareous cements in a wide range of agglutinated foraminifera. The fairly well-developed cement in Rizabdammina parabyssorum (Arabian Sea) and R. abyssorum (NE Atlantic) resembles the 'undifferentiated' cement present in more than half of the species examined by Bender (1995). In both species, the attachment areas of detached particles are clearly visible on cement coated surfaces (PI. 2, Figs 7,8; PI. 3, Fig. 7). In contrast, Bender's (1995) Rizabdammina abyssorum from 400m depth in the Greenland Sea had foam-like cement. There is almost no trace of an organic matrix within the outer test layer of Rhabdammina parabyssorum which is similar to the friable tests of Astrorhiza arenaria (Tendal & Thomsen, 1988; Bender, 1995, pI. 8, fig. I) and Crith ion ina delacai (Gooday et al., 1995a).

Taxonomic implications Cement. Loeblich & Tappan (1989) divided aggluti­nated foraminifera with organic cement into three suborders according to the cement microstructure; a fourth suborder was established to accommodate taxa with secreted calcitic cement. However, Bender (1989, 1995) observed that cement microstructure is not a consistent, well-defined feature and may vary within a genus. She therefore downgraded its taxo­nomic significance and recognised only two suborders of agglutinated foraminifera, one characterised by organic cement (this includes all morphologically simple agglutinated foraminifera so far studied), the other by calcitic cement. At the species level, however, Bender (1995, p. 36) regarded the different types of organic cement microstructure as being con­sistent and therefore 'an important tool for the species concept and recognition of morphospecies'. The present study suggests that this may not always be the case since, as discussed above, both undiffer­entiated and foam-like microstructures occur in Rlzabdammina abyssorum. In fact Bender (1995, p. 30) herself seems to allude to this issue when she

remarks that foam-like cement is not uniformly developed throughout the test of R. abyssorum, 'hampering the classification of the cement type as 'foamy' or 'undifferentiated".

Test wall composition and structure. Rhabdammina parabyssorum and R. abyssorum have identical test morphologies and display the same range of varia­tion, including three-, four-, five-rayed and branched (R. major-like) morphotypes. The two forms could be variants of one species. However, we agree with Stschedrina (1952b) that the striking and consistently different wall structures justify the recognition of two distinct species. If this is correct, then it suggests that sibling species with identical test morphologies exist among foraminifera. The alternative interpretation, that the two forms are conspecific, also has important consequences because it implies that wall structure can vary substantially within a single species. A molecular approach (Pawlowski et al., 1994) may be the only way to establish whether or not R. abyssorum and R. parabyssorum are really genetically distinct entities.

The wall structure in R h a b dam min a parabyssorum also raises important issues at the generic level, as discussed by Stschedrina (1952b). In his definition of the genus Astrorhiza, Hofker (1972, p. 21; see also Loeblich & Tappan, 1987, p. 20) emphasised the thick, sometimes friable test wall composed of many layers of agglutinated particles, so that the external volume of the test is much greater than the internal volume. Astrorhiza granulosa conforms well with this definition. According to Hofker (1972, p. 26), the wall in Rhabdammina is not as thick as in Astrorhiza, is firmly cemented (not friable), and consists of one or more layers of sand grains. This definition fits Rhabdammina abyssorum well but is inconsistent with the nature of the outer test layer developed in R. parabyssorum. The wall structure in this species is closer to that of Astrorhiza species, particularly A. granulosa. Clearly, the diagnosis of Rhabdammina, and the relation between this genus and Astrorhiza, needs to be reconsidered.

Ecological implications There are some striking similarities between the organisation of the outer test layer in Arabian Sea specimens of Rhabdammina parabyssorum and the spherical test of Crithionina delacai from Explorers Cove, Antarctica, as illustrated by Gooday et al. (1995a; PI. 3). In both cases the wall is extremely friable, contains very little cement and is made up of a jumble of quartz grains with a loose, open texture and a large proportion of empty, intergrain space. One difference is that pseudopodia have been observed within the wall of C. delacai but are not obviously present in R. parabyssorum. This could simply reflect the fact that the outer layer in R. parabyssorum is situated away from the apertures

110

and therefore relatively inaccessible to pseudopodia.

Gooday et al. (1995a) suggest that the test wall in Crithionina delacai is an ephemeral structure in a constant state of flux. Similar arguments may apply to the outer layer in R. parabyssorum. The fact that it is variably developed within individual speci­mens, being thick in some areas of the test and absent in others (sometimes with an abrupt junction between the two areas), also suggest that it is a dynamic rather than a static feature. It is possible that these poorly cemented test structures are involved in trophic mechanisms and perhaps represent a response to fluctuating food supply (Gooday et al., 1995a, p. 297). For example, their loose agglutinated construction resembles that of the 'feeding cysts' which are sometimes developed by calcareous and other foraminifera (Arnold, 1979; Linke & Lutze, 1993; Bowser et al., 1995).

We have not examined the outer test layer in Astrorhiza granulosa in such detail. However, the fact that it is consistently developed in all avail­able specimens suggests that, despite being loosely agglutinated, it may be a more permanent structure than the outer layer in Rhabdammina abyssorum.

QUESTIONS FOR THE FUTURE There clearly remains much to be learnt about the biology and taxonomic relationships of apparently simple agglutinated foraminifera (Bowser et al., 1995; Gooday et al., 1997). The present study raises a number of questions.

1) What is the geographical distribution of the two-layered form of Rhabdammina parabyssorum? Do some records of R. abyssorum refer to this species which prior to our study had only been reported from the Sea of Okhotsk and Bering Sea?

2) What is the taxonomic relation between the three species considered in this paper? Is overall test morphology (which would group together Rhabdammina parabyssorum and R. abyssorum) more important than wall structure (which would group together R. parabyssorum and A. granulosa)? Are R. parabyssorum and R. abyssorum really distinct species?

3) What is Rhabdammina major? Is this branched form a variant of R. abyssorum, as sug­gested by Gooday (1986). If so, what is its signifi­cance; for example, is it an ecological variant or a stage in the life cycle?

4) How variable is the cement microstructure within individual agglutinated species?

5) What is the biological function of the two­layered wall structure? Is it related in any way to secondary agglutinated structures such as feeding cysts? Is it involved in the trophic biology of the foraminifer?

A number of approaches might be helpful in addressing such issues. For example, long term

A.J. Gooday & C.W. Smart

culture studies could help to resolve some of the ecological questions while molecular methods might illuminate the taxonomic problems.

ACKNOWLEDGEMENTS We thank Mrs Jane Green, Dr. Roy Moate and the late Dr. Derek Sargeant of the Plymouth University Electron Microscope Unit for their help with SEM. We are particularly grateful to Dr Andrey Gebruk for obtaining copies of the Stschedrina papers and translating important sections of them. This is SOC DEEPSEAS contribution no. 37.

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112 A.J. Gooday & C.W. Smart

Plate 1. Rlwbdnmmina parillly~sor1/l1J Stschedrina from the Arilbi.111 Seil (lJiSCOI'l'rY Stillion 12671#4). 1\11 are SEM photogr<lphs unless otherwise stated. 1. Light photogmph of complete specimen; 2-3. details of Men where inner and outer layers are exposed (arrows point out equivalent positions); 4-5. det,1ils of outer, frinb1e I,'yer composed of very wC'nkly cemented quartz grnins; 6-7. det<li!s of inner layer composed of more firmly cemented quartz grains and sponge spicules. Scale bars == 2 mm (1),500 Jlm (2), 100 Jlm (3,5,6), 50 Jlm (4,7)

Wall structure and morphology of three large tubular foraminifera 113

Plate 2. RJwbdammil1a par(1!'yssona1J Stschedrina from the Arabian Sea (Discovery Station 12671#4). 1-2. Fr(lctured surface of test showing inner layer composed largely of sponge spicules and outer layer composed largely of quartz grains; 3. inner surface showing flat-lying sponge spicules embedded in organic matrix; 4. fractured surface showing inner and outer layers; 5-6. details of outer layer showing virtual absence of organic cement; 7-8. details of inner layer showing well-developed undifferentiated cement; note the scars left on cement covered surfaces by detached grains. Scale bars: 100 tLm (1,2,4,5); lOtL!n (3,6,7); 1 pm (8).

A.J. Gooday & C.W. Smart

Plate 3. RJI(l/ldammillrl Ilbyssontm Sars from the Porcupine Seabight, NE Atlantic (Challenger Station 50606#1). All photographs taken llsing SEM. 1. Complete specimen; 2·3. Details of broken end of tube showing single layered constmction from large quartz grains and fine-grained matrix; 4-5. Outer surface of test showing large quartz grains; 6-7. Broken surface showing matrix particles and undifferentiated cement; note scars left on cement covered surfaces by detached grains. Scale bars: 1 mm {ll, 200 J-tm (2), 100 11m (3-5), 10 Jlm (6,7)

Wall structure and morphology of three large tubular foraminifera 115

Plate 4. Aslrorhiz.(l gmnrllosn Brady from the NE Atlantic (Discovery Station 8973). AI! photographs tilken l1~ing SEM unless othen,,'ise stated. t. Ught photograph of specimen with three ,'pertures; 2. Light photograph of specimen with I'\.\'o apertures; 3,5. Detail of aperturaJ end showing inner layer composed of mineral grains emerging from beneath outer layer composed of juvenile globigerinacean shells; 4,6-7. Details of aliter Jayer. Scale bars: 1 mm (1,2), 100 pm (3,4,6), 50 Jim (5,7).