Journal ofForaminifera1 Research, v. 16, no. 3, p. 216-223, pl. 1, July 1986

THE MORPHOLOGY AND ECOLOGY OF ASTRAMMINA RAM

TED E. DELACA A-002 Marine Biology Research Division, Scripps Institution of Oceanography,

La Jolla, CA 92093

ABSTRACT

Astrammina rara is a large and distinctive aggluti- nated foraminifer. Its abundance and trophic position suggest that it is an influential component of some ben- thic communities around Antarctica. Morphologic measurements of a sample population show that this species typically has a spherical to globular test with from one to several simple or branching tubes (with or without apertures). These tubes have been separated by gross morphology into open ended stolons and closed cones, both of which may be found on the same indi- vidual. On the basis of field and laboratory studies, stolons and cones appear to be feeding structures. These test features were previously thought to be of diagnos- tic importance in the separation of three different gen- era. As a result of this study I infer that the species Astrammina rara, Pelosphaera cornsta and Armorella sphaerica are synonymous.

INTRODUCTION

Foraminifera are abundant constituents of most ma- rine environments, including the deep sea (Hessler, 1974; Smith and others, 1978; Snider and others, 1984) and polar seas (DeLaca and others, 1980). Little is known of the biology of the deep-sea and polar species, the work so far having been restricted to a few distri- butional and taxonomic studies. This presentation is the result of recent investigations into the trophic po- sitions and dynamics of benthic shallow-water (3-32 m) foraminifera in McMurdo Sound, Antarctica. As- trammina rara Rhumbler (in Wiesner, 1932) is an im- portant element of the foraminiferal fauna in several habitats. It is a particularly large agglutinated species, which is dynamic in shallow-water communities and has a wide recorded bathymetric range (Heron-Allen and Earland, 1932). Though it was described in 1931, there has been some confusion in the literature as to the nature of certain diagnostic features of its test. The purpose of this paper is to describe the morphology and ecology of this species.

LOCALITY

McMurdo Sound is located in the southernmost part of the Ross Sea at latitude 77"s and longitude 166"W. The eastern and western (south of Marble Point) sides of the sound differ in water circulation (Fig. 1) and duration and thickness of ice cover. These dissimilar- ities account for significant differences in the amount of organic material reaching the benthos. The eastern side of the sound receives large amounts of current- borne organic materials, which originate to the north in the more ice-free regions of the Ross Sea. In situ

216

water column and benthic production becomes no- ticeable late in the season. Explorers Cove, the site of this study (Fig. l), is on the western side of the sound and receives no current-borne organics. In situ pro- duction is less pronounced and occurs later in the sea- son. There are several sources of organic input to the study area, including the epontic algae of the sea ice, plankton, shallow-water benthic algae, and algal mats in ice-free shallow-water areas along the periphery of the cove. Total production in Explorers Cove is low compared to that of the eastern sound.

The sea bed in Explorers Cove is a gently rolling sand and mud bottom with occasional glacial-erratic boulders to depths of at least 40 m. The bottom is dimpled with many small, shallow depressions, prob- ably created by the activities of larger benthic organ- isms, especially the free living scallop Adamussium colbecki. Sediments in Explorers Cove are coarser than the diatomaceous oozes and glacial flour commonly found in deeper water around Antarctica. Benthic dia- tom growth produces a thin pigmented film over the sediment to a water depth of approximately 18 m in the late summer. Just above the sediment, water tem- perature was - 1.86"C and salinity was 34.6%.

The New Harbor environment (Fig. 1) has been lik- ened to the deep sea on the basis of faunal affinities and patterns of abundance and diversity, as well as its documented oligotrophic nature (Dayton and Oliver, 1977; DeLaca and others, 1980; Hodson and others, 198 1; Holm-Hansen and others, 1977). Productivity patterns have changed somewhat since the surveys of the late 1970's which produced this literaure. Prior to 1980, the sea ice covering extensive regions of the west- ern side of the sound (including Explorers Cove) had remained in place for more than eight years and reached thicknesses of more than five m. The thickness of this ice greatly reduced the amount of light that penetrated the water and, therefore, suppressed in situ productiv- ity. The sea ice has broken out from New Harbor an- nually in the very late summer, since 1980, and is thinner, allowing higher late-summer productivity. This type of episodic event in near-shore Antarctic envi- ronments has produced obvious changes in the distri- butions and standing stocks of benthic foraminifera (DeLaca, unpublished data).

MATERIALS AND METHODS

COLLECTION Samples were collected from Explorers Cove on the

western side of McMurdo Sound. The specimens used in this study were obtained by diving with SCUBA. Collections were made in several ways, depending on

MORPHOLOGY AND ECOLOGY OF ASTRAMMZNA RAM 217

401

Test diameter ( m m )

FIGURE 1 . McMurdo Sound, Ross Sea, Antarctica. The speci- mens used for this study were collected from Explorers Cove, New Harbor (77"S, 166"W). The arrows indicate the probable direction of current flow.

the object of the study. Bulk samples for population size-frequency and morphology measurements were collected by gathering the top three cm of sediment into one-gal Nalgenem jars. The organisms were then taken to the laboratory and sieved over a nested set of stainless steel sieves (0.063,0.500, 1.00, and 5.00 mm), using a gentle stream of cold seawater. The animals were sorted from the various residues with the aid of "Live Insect Collecting Forceps" (Fine Science Tools) and placed in petri dishes for measurement.

A census of the populations was accomplished by randomly placing 100 cm2 cores into the sediment. The location of the cores relative to one another and to depth, and local topographic and biological features were noted. The cores were washed through nested sieves and the A. rara counted and measured.

In situ fixations were accomplished in 100 and 18.9 cm2 cores placed in the sediment. Using SCUBA, the coring tubes were manually inserted into the sediment to depths of approximately 10 cm and the open ends capped. While still in place, glutaraldehyde or form- aldehyde (final concentration 24%) was added. After variable intervals (tens of minutes to several hours) the cores were removed from the sediment; the bot- toms of the tubes were sealed; the tubes were taken to the laboratory. Individual foraminifera were carefully removed by eroding the sediment with a tiny stream of water. Some of the fixed material was post-fixed in osmium tetroxide, and then serially dehydrated with

FIGURE 2. Astrammina rara. Size-frequency histogram of ani- mals taken from 28 m in Explorers Cove.

ethyl alcohol. Specimens to be examined with the scan- ning electron microscope were placed in amyl acetate and transported to the Scripps Institution of Ocean- ography, where they were critical-point dried using liq- uid CO,. Other specimens were embedded in Spurr's low-viscosity resin (Poly-Sciences Inc.) and ground and polished using carborundum, diamond and aluminum oxide abrasives. The organic material was stained us- ing Azure II/Methylene Blue, Methylene Blue in borax (Richardson and others, 1960). Alcian blue in acetic acid was used to further differentiate the acid muco- polysaccharides ofthe test (Spicer, 1963). Several thou- sand specimens were examined during the course of physiological and ecological investigations.

Measurement of test diameter and the lengths of the various test processes were made by using an ocular grid or an ocular micrometer with a Wild dissecting microscope. These scales were calibrated with stage micrometer and are accurate to 0.01 mm.

Gross chemical composition was assayed using the quantitative micro-analytical procedures for protein, lipid and carbohydrate (Holland and Gabbott, 197 1; Holland and Hannant, 1973). Spectrophotometric measurements were made with a Perkin-Elmer model 5 52 spectrophotometer. Organic carbon determina- tions were made with a Hewlett Packard 185B CHN analyzer using disodium ethylene diamine tetra-acetic acid as primary standard.

Biomass estimates were made from analyses of aden- osine triphosphate (ATP) of foraminifera isolated from sampling cores. Nucleotide extraction was accom- plished by introducing living organisms (maintained at 0°C prior to extraction) simultaneously with five ml of 100°C citrate-phosphate buffer, pH 7.2 (Bullied, 1978), into preheated test tubes followed by immediate disruption with a pre-heated frosted glass pestle. Stan- dard ATP analyses were made using an SA1 (Model 2000) photometer. Biomass estimates were derived from previously determined ratio of ATP to total car- bon.

218 DELACA

seawater

I reticulopodial et OrWn ,% network

A

FIGURE 3. A. Composite drawing of Astrammina rara as it is usually found in the sediments. The membrane-bound sarcode is suspended within the agglutinated test. Pseudopodia originate from the single aperture of the imperforate inner organic membrane. Fine reticulopodial networks surround the sarcode within the agglutinated test or extend through stolons or cones into the surrounding sediments. B. Spherical agglutinated test with stolon and cones. C. Subspherical test with two cones.

RESULTS TEST MORPHOLOGY

Central Chamber Astrammina rara is a large (0.53 to 4.56 mm di-

ameter x = 2.13, SD = 0.7153 mm, n = 138) (Fig. 2) and distinctive agglutinated foraminifer. Smaller in- dividuals were not easily distinguishable from other small spherical foraminiferal species of the genera Psammosphaera and Saccammina (known to co-exist in this region) without resorting to dissection so they were not studied. The test of A. rara is spherical to globular and composed of fine to coarse sand grains held in place by large quantities of brown to gray ce- ment. The single-chambered test has from one to five radiating projections of varying configuration (Pl. 1). Small specimens with one or two test projections may appear fusiform (Fig. 3). The test walls of most spec- imens are composed of coarse (1 mm) to fine (0.0625 mm) subangular to rounded sand grains. Quartz is the

major mineral; feldspars, micaceous minerals and rock fragments comprise the remaining grains. Larger sand grains as well as very fine (silt and clay sized) particles, diatom frustules and sponge spicules are incorporated in test construction. Choice of material seems to de- pend largely on the composition of the substrate. The grains are usually arranged in a single layer, but in some individuals the test is three particles thick. Larger sand grains often abut, and all sediment particles are firmly bound with cement. Grain surfaces are entirely covered with a fibrous organic material (Fig. 4A), and larger volumes of cement are used between the grains on the outer surface of the test. The voluminous accumulation of cement gives the outer surface of the test a polished appearance. The interior surface has less cement and is consequently more irregular (Fig. 4B). The rigidity of the test depends upon the size of the specimens. Specimens as large as 2-3 mm in diameter are resistant to deformation and cracking only after considerable pressure is applied. Larger specimens (up to 6.5 mm) are flexible and tear under compression.

MORPHOLOGY AND ECOLOGY OF ASTRAMMZNA RARA 219

The binding properties of the cement for the stain Alcian blue indicate the cement to be an acid muco- polysaccharide. Organic carbon constitutes approxi- mately 0.35% of the test’s dry weight. This organic material has a CarbonNitrogen ratio of 10.44 and is composed of 8.5% protein, 59.7% carbohydrate, and 18.8% lipid.

From one to five projections of varying length and configuration are present on the otherwise spherical test. There is no obvious pattern to sand grain or ce- ment organization within the test wall in the area where projections arise. In some specimens the test bends in an outward fashion forming a wide aperture in the wall, from which the process extends (Pl. 1C). In other spec- imens, the only obvious modification is the absence of cement between the sand grains in the wall at the base of the projection; the process arises from an oth- erwise unaltered test surface (Pl. lA, B and D).

Three distinctively different types of projections arise from the test of A. rara; stolons, cones and buds (Pl. 1). In superficial examination of the tests, these pro- cesses appear as: 1) long unbranching or branching open tubes; 2) somewhat shorter, tapering, closed pro- cesses; and 3) small blisters on the exterior surface of the test. In the sample population measured (Fig. 2), 51.5% of the individuals possess stolons, 85.5% pos- sess cones, 38.4% possess both stolons and cones, and 10.1% possess buds. When an individual has more than one process extending from its test (8 1.2% of the sample population), the processes frequently are ori- ented in a single plane (56.2%). Randomness is ap- parent in the remaining portion of the population.

Stolons Stolons are relatively thick-walled, tubular, open-

ended extensions of the test. They vary considerably in outward appearance, length and composition (Pl. 1 A, B), and are composed of a wide range of inorganic materials, including medium to fine grained sand, silt, clay, diatom frustules, and fragments of sponge spic- ules. In general, coarser material is found at the base of the stolon and finer material at the distal ends. This inorganic material may be arranged in from one to several particles thickness and is bound together with copious amounts of cement. Though typically rigid, exceptionally long stolons, composed of mostly organic material, are very flexible and easily collapse or break if handled roughly. Longer stolons are occasionally branched. Of the population measured for this study, 51.5% have from one to three stolons (median = 1). They range in length from 0.24 mm to 4.80 mm (x = 0.62, SD = 0.050). There is no correlation between the diameter of the test and the presence or number of stolons (r = 0.2065, n = 71) [critical value at 5%, v = 69 is 0.2321.

Cones The term “cones” refers to conical processes that

project away from the test. These processes are hollow tubes, closed at their distal ends (Pl. 1 C and D). While

FIGURE 4. A. Scanning electron micrograph of broken test wall. All inorganic components are covered with fibrous organic material and firmly bound together. B. Thin section stained with Alcian blue shows accumulation of organic cement on outer surface of the test (bottom of photograph).

there is considerable variation in size, shape and tex- ture, an obvious ground-plan is discernable. They range in length from 0.20 to 2.2 mm (x = 0.36 mm, SD = 0.02). The longest is equal to the diameter of the test and is somewhat flexible at its tip. The shortest is little more than a hemispherical blister on the side of the test. Longer cones occasionally terminate in lightly ag- glutinated flexible extensions that may bifurcate into fine ribbons.

The conical shape of the cones results from the in- creased thickness of the wall at its attachment to the test and the thinner walled tapering tip. In contrast, the interior diameter of the tube is frequently uniform for much of its length. The walls are generally com- posed of a variety of inorganic materials, including all of those listed above for stolons. The coarsest material

220 DELACA

PLATE 1 A, B Thin sections of specimens embedded in epoxy show stolons arising from the test of Astrammina rara. The stolons incorporate coarser

inorganic material than cones and are open ended (the long and flexible tip of the stolon in A was not within the plane of section and therefore appears closed). Specimens show no significant modifications of test wall where stolon originates. C, D Thin sections of cones. Conical appearance results from thickening at the base and thinness of distal end. The interiors are often of uniform diameter. While no aperture is

MORPHOLOGY AND ECOLOGY OF ASTRAMMZNA RARA 22 1

occurs immediately near the base. Unlike the test wall, however, larger sediment grains do not usually abut, for the grains are surrounded by greater amounts of organic material. There is a rapid shift to the very fine material towards the distal ends. The wall is thinnest at the tip of the cone and thickest at the base. Apertures are not apparent using light- or scanning-electron mi- croscopy. The tips are less well consolidated. Fine cy- toplasm may protrude from the tips of cones of in situ fixed material, thereby demonstrating their porous na- ture. The outside surface is smoothed by greater ac- cumulation of organic material. In cross section, the interiors are rougher in appearance. From one to five (median = two) cones are present in 85.5% of the sam- pled population. There is no correlation between the diameter of the test and the presence or number of cones (r = 0.1595, n = 118) [critical value at 5%, v = 116 is 0.1951. Both cones and stolons are present on 38.4% of the population.

Buds Buds are small hemispherical to spherical processes

constructed of very fine sand cemented in a single layer (Pl. 1E). There is very little organic material on the outside of the structure and the exterior is, therefore, rough. Diameters range from 0.1 to 0.5 mm. Buds have been found only on individual A. rara larger than 1.8 mm diameter. Because of their small size, buds may easily be overlooked or mistaken for irregular, multi- faceted sand grains. From one to five buds are present on 10.lo/o of the population. Buds may separate from the “parent test” in undisturbed laboratory vessels and may move about independently.

ORGANIZATION OF THE SARCODE The protoplasm of Astrammina rara consists of a

membrane-bound main protoplasmic body (MPB) that resides within the test, and thick and thin pseudopodia that extend through the various test processes into the external environment. The MPB is cream to brown and usually occupies the center of the test chamber. Thin section and dissection observations show that the amount of interior test space occupied by the MPB ranges from 25 to 100% of the inner test volume.

The main protoplasmic body of A. rara is bound by a 2.5 to 10 pm thick, imperforate, organic membrane, which has a single oral region. This inner membrane and the protoplasm it contains are superficially similar in appearance to Allogromia. This type of configura- tion has only been reported for two species of agglu- tinated foraminifera, Pelosphaera cornuta Heron-Al- len and Earland (Hedley, 1960) and Pilulina argentea (Christiansen, 197 1). Protoplasm within the inner shell

includes a single large (up to 0.2 mm diameter) nucleus and variable amounts of sediment and diatom frus- tules. All of the pseudopodia originate from the single aperture of the inner protenaceous shell. Small pseu- dopodia were often found surrounding the MPB within the test. Larger pseudopodial masses extend through test processes to the exterior. Examination of in situ fixed material and A. rara in rough culture reveals large pseudopodia that extend through the stolons and con- tinue through the sediment as a single thick bundle of cytoplasm for distances as great as 5 cm. At the termini of these thick pseudopodia, the cytoplasm ramifies into the classic reticulatinglanastomosing reticulopodial network reported for other foraminifera (Allen, 1964; Arnold, 1955). I have seen cytoplasm extend only a few millimeters from the tips of cones, in clumps or as a fine pseudopodial network.

The protoplasm occupying the interior of the buds contains a single nucleus and is membrane bound (Pl. 1E). This body may be in communication with the “parent test” or may be isolated from it. Casual ob- servation of these features indicates that the buds are reproductive structures.

DISTRIBUTION AND ABUNDANCE Astrammina rara is found on both sides of Mc-

Murdo Sound and extends from depths of 18 m to the deepest depth surveyed (32 m). Its distribution is lim- ited to well-oxygenated, coarse to fine grained sands having a significant siltklay fraction and relatively high organic content. It does not occur in coarser sediments or in areas of obvious in situ benthic productivity (pig- mentation obvious to the unaided eye). In general, distribution is extremely patchy. Standing stocks ranged from 0 to 1,800 individuals per square meter in the depth range of 28 to 32 m. The largest populations were found in topographic depressions in deeper water and around boulders. In these habitats, A. rara was a conspicuous component, having abundances of 400 to 1,800 individuals per square meter (x = 1,058, SD = 493, n = 12), and representing a wet biomass (proto- plasm) of 4.2 g with 3.2 g (wet weight) of organic ma- terial in tests. These environments are characterized by higher concentrations of particulate organic-carbon, bacteria, and dissolved organic-material, and larger micro- and meio-faunal standing stocks than adjacent regions. Other foraminifera occurring in these envi- ronments are listed in Table 1.

Larger specimens of A. rara were usually found 0.2 to 1.0 cm below the sediment surface; radiating pro- cesses were oriented parallel to the sediment surface. Careful dissection of in situ fixed cores revealed large pseudopodial masses extending from one or two of the radiating stolons (where present). This cytoplasm com-

apparent, the tips are porous and fine pseudopodia radiate from them. E Membrane-bound sarcode with nucleus and pseudopodia within a thin walled spherical “bud” on the surface of the parent test. This section is somewhat thicker than those previously presented to preserve protoplasmic detail.

222 DELACA

TABLE 1. Species of benthic foraminifera found with Astramminu rara. Relative abundances within this assemblage are given in pa- rentheses.

Abundant (> 15%) Cassidulinoides porrecta (Heron- Allen and Earland) Globocassidulina cf. G. biora (Crespin)

Cibicides refulgens (DeMontfort) Cribrostomoides jeffreysi (Williamson) Miliammina arenacea (Chapman) Portatrochamminu antarctica (Parr) Pullenia subcarinata (d'orbigny) Reophax subdentaliniformis Parr Rosalina globularis d'Orbigny Trochammina ochracea (Williamson) Uvigerina bassensis (Parr)

Astrorhiza limicola Sandahl Bolivina sp. Ehrenbergina glabra (Heron-Allen and Earland) Epistominella exigua (Brady) Fursenkoina earlandi (Parr) Glandulina antarctica Parr Haplophragmoides canariensis (d'orbigny) Notodendrodes antarctikos DeLaca, Lipps and Hessler Parajissurina marginata (Wiesner) Pseudobolivina antarctica Wiesner Pseudobulimina chapmani (Heron-Allen and Earland) Pyrgo inornata (d'orbigny) Reophax ditflugiformis (Brady)

Common (2-1OYo)

Rare (< 2%)

monly extended through the upper few millimeters of the sediment for up to five centimeters away from the test as discrete bundles and, thence, radiated into the more classic reticulopodial network near the terminus. Other smaller pseudopodial arrays extended from cones a few millimeters into the surrounding sediment. In regions o f high A. rara densities, pseudopodia occupied large volumes of the surface sediments. Similar de- ployment patterns were observed in living laboratory specimens. Pseudopodia of in situ fixed specimens and specimens taken from rough culture vessels contained a variety of pennate diatoms, bacteria, small meta- zoans and amorphous organic and inorganic materials. Field and laboratory observations indicate that smaller specimens of A. rara (0.5 to 1.5 mm in diameter) are more motile and occur in greater abundance at the sediment surface than larger specimens.

DISCUSSION Astrammina rara is a large and distinctive aggluti-

nated foraminiferan. Measurement of a sample pop- ulation of 183 individuals and observations on thou- sands of other individuals indicate that this species typically has a globular test composed of coarse to fine sand and other very fine inorganic grains. The inor- ganic grains are held together firmly by copious amounts of brown to gray cement. The simple test wall most often consists of a single layer of sand grains that forms a central chamber, from which one or more simple or branching tubes (with or without apertures) extend. The apertures are terminal and circular. The tubular extensions may be separated by gross morphology into

three categories: open ended tubes (stolons), tapering tubes with closed ends (cones), and smaller hemispher- ical to spherical blisters (buds). There is no significant correlation between the test diameter and the number or type of tubular extensions present. Dissection, thin sectioning, and observation of living and in situ fixed specimens indicate that stolons and cones are involved in pseudopodial deployment and feeding. Pseudopodia arise from the tips of cones and extend into the sedi- ment where ramified networks collect and assimilate small unicellular organisms, including bacteria and unicellular algae. Long ropy pseudopodia pass through stolons to range through and across the sediment, where their ends ramify into more classical looking reticu- lopodial networks. These pseudopodia are as long as 5 cm and capture large prey, including metazoans (up to 1.5 cm), as well as small organic particulates. Buds are reproductive structures and do not appear to be involved with feeding. Stolons are present on 5 1.5% of the studied population, while 8 5.5% have cones and 10.1% have buds. Both stolons and cones were present on 38.4% of the population.

Extra-cameral extensions of the type described above have been used as primary taxobases in distinguishing three species, Astrammina rara, Armorella spherica Heron-Allen and Earland, and Pelosphaera cornuta Heron-Allen and Earland. Astrammina rara and Ar- morella sphaerica are described as having open ended stolons and were previously synonymized by Loeblich and Tappan ( 1 964). The synonymy was later refuted by Hofker (1972). Pelosphaera cornuta is similar to these species, but has cones rather than stolons, and is reported to have an inner membrane-bound sarcode having a single aperture (Hedley, 1960). Pelosphaera cornuta is presently included in the family Saccam- minidae. It seems very likely from the present study and examination of original descriptions that these three "species" should be assigned to the same species be- cause: l ) the characteristics used to separate them are not mutually exclusive, but may be found in a single individual, and; 2) all three species were originally col- lected and described from the same geographic region (subantarctic islands).

The name Astrammina rara has priority for the fol- lowing reasons: 1) of the three genera considered, As- trammina is the earliest named (1 93 1) (Armorella and Pelosphaera, 1932), and; 2) it bears closest similarity to the type genus and species Astrorhiza limicola San- dah1 (1 858) of the family Astrorhizidae. Astrorhiza limicola occurs with Astrammina rara at New Harbor and differs only in that the central chamber is a flat- tened hollow disc, and the projecting processes com- monly have open ends. Conical processes are also pres- ent in A. limicola.

All of the species discussed above more closely fit the criteria given for the family Saccamminidae than the family Astrorhizidae. The basic structure of these species is the subglobular test, which is diagnostic of the Saccamminidae. Tubular forms are typical of the Astrorhizidae. The forms, lengths and numbers of tu- bular (open or closed) processes radiating from the

MORPHOLOGY AND ECOLOGY OF ASTRAMMZNA RAM 223

spherical to subglobular shells appear to vary in re- sponse to environmental and ecological factors rather than being an obligatory feature of the species. The morphologic similarity of the smaller specimens, asex- ually produced (budded) young, and the membrane- bound sarcodes residing in the agglutinated shells of A. rara, further suggest affinity to typical genera (Psam- mosphaera and Saccammina) of the Saccamminidae.

CONCLUSION

Astrammina rara is a conspicuous and influential component of the shallow-water benthos in New Har- bor and even extends down to 3,705 m (Heron-Allen and Earland, 1932, listed as P. cornuta). It is most abundant at depths of 28 to 32 m at Explorers Cove. Individuals within the sample population range from 0.5 to 4.75 mm in diameter. Other specimens mea- sured during the course of this and related studies reach diameters of 6.5 mm. In combination with the extra- cameral projections (stolons or cones), the maximum dimension may reach 11 mm. Pseudopodia are de- ployed through the cones and stolons, and undoubtedly facilitate feeding. While pseudopodial networks arising from cones extend only a few millimeters, bundles of cytoplasm emanating from stolons can reach 1 mm in diameter and extend as far as 5 cm away from the test. In certain microenvironments of Explorers Cove, A. rara reaches densities of up to 1,800 individuals per square meter. Examination of biological tissue from in situ fixed cores indicates that the sediment in these “optimal” microenvironments contains numerous fo- raminiferal pseudopodia.

Astrammina rara uses dissolved organic material di- rectly, consumes fine particulate organic material, in- cluding a variety of bacteria and unicellular algae, and captures and devours small benthic metazoans. By vir- tue of its abundance, biomass, and trophic position, Astrammina rara must be considered an important component of the antarctic shallow-water benthos.

ACKNOWLEDGMENTS I thank J. M. Bernhard, W. L. Stockton, J. J. Val-

encic, and K. A. Miller for field assistance and com- pany during diving. Field operations were supported by the U.S. Naval Support Force, Antarctica and ITT Antarctic Services, Inc. This manuscript benefitted from the suggestions of J. M. Bernhard, W. L. Stockton, H. T. Loeblich and A. R. Loeblich. This research was supported by National Science Foundation grant DPP83-0547 5.

REFERENCES

ALLEN, R. D., 1964, Cytoplasmic streaming and locomotion in marine foraminifera, in Kamiya, N., and Allen, R. D. (eds.). Primitive Motile Systems in Cell Biology: New York, Academic Press, p. 407-432.

ARNOLD, 2. M., 1955, Life history and cytology of the Foraminifera Allogromia laticollaris: University of California Publications in Zoology, V. 61, p. 167-252.

BULLIED, N. C., 1978, An improved method for the extraction of adenosine triphosphate from marine sediments and seawater: Limnology and Oceanography, v. 23, p. 174-178.

CHRISTIANSEN, B., 197 1, Notes of the biology of foraminifera: Vie et Milieu suppl. 22, p. 465-478.

DAYTON, P. K., and OLIVER, J. S., 1977, Antarctic soft-bottom benthos in oligotrophic and eutrophic environments: Science,

DELACA, T. E., LIPPS, J. H. and HESSLER, R. R., 1980, The mor- phology and ecology of a new large agglutinated Antarctic for- aminifer (Textulariina: Notodendrodidae nov.): Zoological Journal of the Linnean Society, v. 69, p. 205-224.

HEDLEY, R. H., 1960, New observations on Pelosphaera cornuta: Contributions from the Cushman Foundation for Foraminiferal Research., v. 11, p. 54-57.

HERON-ALLEN, E., and EARLAND, A., 1932, Some new foraminifera from the South Atlantic, IV. Four new genera from South Geor- gia: Journal of the Royal Microscopical Society, London, v. 52,

HESSLER, R. R., 1974, The structure of deep benthic communities from central oceanic waters, in Miller, C. B. (ed.), The biology of the Oceanic Pacific: Corvallis, Oregon State University Press, p. 79-93.

HODSON, R. E., AZAM, F., CARLUCCI, A. F., FUHRMAN, J. A., KARL, D. M., and HOLM-HANSEN, O., 1981, Microbial uptake of dissolved organic matter in McMurdo Sound, Antarctica: Ma- rine Biology, v. 61, p. 89-94.

HOFKER, J., SR., 1972, Primitive agglutinated foraminifera; Leiden, E. J. Brill, 95 p.

HOLLAND, D. L. and GABBOTT, P. A., 1971, A micro-analytical scheme for the determination of protein, carbohydrate, lipid and RNA levels in marine invertebrate larvae: Journal of the Marine Biological Association, United Kingdom, v. 5 1, p. 659- 668.

-, and HANNANT, P. J., 1973, Addendum to a micro-analyt- ical scheme for the biochemical analysis of marine invertebrate larvae: Journal of the Marine Biological Association, United Kingdom, v. 53, p. 833-838.

HOLM-HANSEN, O., AZAM, F., CARLUCCI, A. F., HODSON, R. R., and KARL, D. M., 1977, Microbial distribution and activity in and around McMurdo Sound Antarctic Journal of the United States,

LOEBLICH, A. R., JR., and TAPPAN, H., 1964, Sarcodina, chiefly “Thecamoebians” and Foraminiferida, in Moore, R. C. (ed.), Treatise on Invertebrate Paleontology: New York and Law- rence, KS, The Geological Society of America and the Univer- sity of Kansas Press, Part C, Protista (2), 2V., 700 p.

RHUMBLER, L., 1935, Rhizopoden der Kieler Bucht, gesammelt durch A. Remane, Tiel I. Natunv. Ver. Schleswig-Holstein, Schrift., G e l Universitat, Leipzig, Bd. 21, p. 173.

RICHARDSON, K. C., JARETT, L. and FINKE, E. H., 1960, Embedding in epoxy resins for ultrathin sectioning in electron microscopy: Stain Technology, v. 35, p. 3 13-323.

SANDAHL, O., 1858, Tva nya former af Rhizopoder: K. Veten- skaps.-Akad., rorhandl. Ofers., v. 14, p. 299-303.

SMITH, K. L., JR., WHITE, G. A., LAVER, M. B., and HAUGSNESS, J. A., 1978, Nutrient exchange and oxygen consumption by deep- sea benthic communities: preliminary in situ measurements: Limnology and Oceanography, v. 23, p. 997-1005.

SNIDER, L. J., BURNETT, R. R., and HESSLER, R. R., 1984, The composition and distribution of meiofauna and nanobiota in central North Pacific deep-sea area: Deep-sea Research, v. 3 1,

SPICER, S. S., 1963, Histochemical differentiation of mammalian mucopolysaccharides: Annals of the New York Academy of Sciences, v. 106, p. 379-388.

WIESNER, H., 193 1, Die Foraminiferen der deutschen Sudpolar Expedition 1901-1903; Deutsche Sudpolar Expedition 1901- 1903: herausgegeben von Erich von Drygalski. v. 20, 2001. v.

V. 197, p. 55-58.

p. 253-261.

V. 11, p. 29-32.

p. 1225-1249.

12, p. 53-165, pl. 1-24.

Received 8 July I985 Accepted 3 September I985