Syringammina corbicula is a species of xenophyophore (Foraminifera) that was discovered living at 3106-meter water depths on the Cape Verde Plateau, off West Africa (Pawlowski et al. 2003, Richardson 2001). This species possesses a hemispherical test comprised of anastomosing agglutinated tubes. Unique basket-like depressions rim the periphery of the test. Like other xenophyophores, S. corbicula possesses: granellae (intracellular barite crystals), granellare (cytoplasm enveloped by a thin organic wall), and stercomata (stercomes enclosed within a membranous casing). Like other foraminiferans, S. corbicula possesses granuloreticulose pseudopodia that it extrudes through openings in the test wall. Syringammina corbicula occupies an epibenthic habitat and captures suspended food particles in the web of pseudopodia that stretches between the branches of its tubular test.
Syringammina corbicula extrudes thick, sticky strands of granuloreticulose pseudopodia through loosely agglutinated and broken regions of the test wall (Richardson 2001). The pseudopodial strands have been observed to stretch and hang across the openings in the latticework of the reticulated test, and presumably function in food capture.
The cytoplasm of living cells is enclosed in membrane-bound tubes called granellare. The granellare of live specimens of S. corbicula are translucent and light yellowish in color (Richardson 2001).
Barite crystals (also known as granellae) have been observed in squash preparations of the membrane-bound branching tubes of cytoplasm (or granellare), and in the membrane-bound tubes of stercomes (stercomare or stercomata), of live specimens of Syringammina corbicula (Richardson 2001). Under the compound microscope, the barite crystals are transparent and colorless, rounded to elongate to occasionally hexagonal in shape, and range in size from <2 µm in diameter to 12 × 20 µm (width × length). The crystals are evenly distributed throughout the cytoplasm, occurring in densities of about 4 crystals per 100 µm2 of cytoplasm. Barite crystals are also sparsely distributed within the stercomare. Individual crystals are located inside the tube-like outer organic membrane of the stercomare, but separate from the stercomes (pellets of waste).
No information is currently known about details of the cell structure of S. corbicula, including the number of nuclei.
The tests of Syringammina corbicula are hemispherical in shape, and comprised of a mass of anastomosing, agglutinated tubes (Richardson 2001). The base of the hemispherical test rests on the sediment surface, with the anastomosing tubes radiating outward and up into the water column. The tubular branches of the test are circular, subcircular to oval in cross-section; however, the tubes may be flattened into plate-like elements, particularly in regions of the test where two or more tubes fuse together. In the distal reaches of the test, the plate-like elements are arranged in basket-like depressions that open outwards toward the test periphery. The holes between the branches are square to pentagonal to hexagonal in shape.Test growth appears to take place in a radial direction, with the basket-like depressions characterizing the outermost, and presumably youngest zone of the test. The distal portions of single tubes often terminate in a rounded or blunt cap or protuberance.
Air-dried tests are yellowish gray in color (Richardson 2001). The test wall ranges from 160-200 µm in thickness and is comprised of coarsely agglutinated adventitious material (xenophyae) embedded in a fine-grained matrix. The ratio of matrix to xenophyae is high, with the xenophyae distributed haphazardly throughout the fine-grained matrix. The coarse-grained xenophyae are almost exclusively comprised of the tests of adult planktonic foraminiferans, while the fine-grained matrix is comprised predominantly of juvenile planktonic foraminiferans, supplemented by minor amounts of irregular mineral grains and radiolarian skeletal fragments. The shells of planktonic foraminiferans, such as Globorotalia menardii (Parker, Jones and Brady, 1865), protrude from the surface of the outer test wall, often with the keel oriented perpendicular to the test wall of the xenophyophore. The shells of other planktonic foraminiferal species that make up the larger xenophyae in the test wall of S. corbicula include: Globorotalia hirsuta (d’Orbigny 1839), G. scitula (Brady 1862), Globigerinoides sacculifer (Brady 1877), and Pulleniatina obliquiloculata (Parker and Jones 1862).
The interior of the tubular test contains granellare (cytoplasm enveloped by a thin organic wall), granellae (intracellular barite crystals), and stercomare or stercomata (stercomes enclosed in a membranous casing) (Richardson 2001). The granellare of live specimens are translucent in appearance and light yellowish in color. Multiple strands (3-6) of granellare occur within a single tubular branch of the test; the strands are located along the periphery of the test lumen, and closely appressed to the interior test wall. The tubes bifurcate frequently, and occasionally anastomose, within a single tubular segment of the test. The granellare branches vary in shape from a cylindrical to a flattened tube, and range from 50-100 µm in breadth. The cytoplasm almost entirely fills the internal lumen of the outer granellare tube throughout most of its observed length. Occasionally, granellare branches terminate in a bulbous structure with thin, thread-like strands of cytoplasm radiating from the terminus. The exterior surfaces of the granellare are ornamented with longitudinally oriented linear ridges and striations, although these features may be artifacts of fixation and/or dehydration.
The stercomare of live individuals are dark brown to black in color and single, branched, and/or anastomosing tubes, and occupy 50-80% of the volume of the internal test lumen (Richardson 2001). The delicate membrane drapes over and encloses the stercomes (waste pellets), which are tightly packed in the stercomare interior at densities as high as 550,000 per cubic millimeter. Individual stercomes are spherical to ovoid in shape and measure from 10-20 µm in diameter. Individual stercomes occasionally contain a single, round, reddish-brown body. The matrix of the stercomes is made of closely-packed non-crystalline plates that are concentrically arranged over the surface of the pellet. Identifiable material within the stercomes includes: coccoliths and coccolith fragments, radiolarian skeletal debris, and diatom frustules. A single harpacticoid copepod was found associated with the stercomes in one preparation.
Molecular phylogenetic analyses using partial small subunit (18S) ribosomal DNA sequences have shown that Syringammina corbicula, and other xenophyophores, branch as subclade within the more inclusive clade Foraminifera (Gooday et al. 2011, Lecroq et al. 2009, Pawlowski et al. 2003). Within the xenophyophore subclade, Syringammina corbicula branches as the sister group to a clade comprised of the xenophyophores Shinkaiya lindsayi + Reticulammina cerebreformis(Gooday et al. 2011, Lecroq et al. 2009). Aschemonella ramuliformis branches as the sister to a clade comprised of Syringammina corbicula + Shinkaiya lindsayi + Reticulammina cerebreformis (Gooday et al. 2011). And, the stercome-bearing foraminiferan Rhizammina algaeformis branches as the most basal taxon in the xenophyophore subclade of Foraminifera (Cartwright et al. 1989, Gooday et al. 2011).In a more recent molecular phylogeny of Foraminifera, an unidentified “allogromiid” foraminiferan (Clade A), together with S. corbicula and the other sequenced xenophyophores (Clade C), comprise a monophyletic clade (Clade A + Clade C) that branches as the sister group to the multi-chambered crown clade “Globothalamea” (Pawlowski et al. 2013).
The test size of Syringammina corbicula specimens collected-to-date ranges from 4-6 cm in diameter. The hemispherical test of the holotype of Syringammina corbicula measured 4 cm x 3.8 cm x 2.9 cm when initially collected, and the test of the figured paratype measured 4 cm x 3 cm x 2 cm (Richardson 2001). Xenophyophores measuring 6 cm in diameter are identified as S. corbicula and figured in Laureillard et al. (2004: Figure 1).
Syringammina corbicula was described and figured by Richardson (2001: p. 202, Figures 1-2, Plates 1-2). The type specimens are deposited in the Cushman Collection for Foraminifera, National Museum of Natural History, Smithsonian Institution, Washington, DC. The holotype (USNM 496757) was fixed in buffered formalin and is stored in alcohol. The figured paratype (USNM 496758) is a dried specimen. The type specimens were collected in December 1998 during Cruise 159, Leg 7 of the RV Knorr (Woods Hole Oceanographic Institution). Sediment samples containing the xenophyophores were collected using a Benthos multicorer from 3106-m water depths on the Cape Verde Plateau (18° 27.7’ N, 21° 01.6’W), off the coast of Mauritania, NW Africa in the eastern Atlantic Ocean.
