Stannophyllum aff. granularium Tendal, 1972

Holzmann, Maria, Barrenechea-Angeles, Inés, Lim, Swee-Cheng & Pawlowski, Jan, 2024, New xenophyophores (Foraminifera, Monothalamea) from the eastern Clarion-Clipperton Zone (equatorial Pacific), Zootaxa 5419 (2), pp. 151-188 : 180-183

Stannophyllum aff. granularium Tendal, 1972

Figs 14 , 15

Material examined. Box core 10, specimen RC0489 (morphology and genetics). Box core 15, specimen RC0608 (morphology). Sequenced isolates: 21445, 21446

Descriptions.

RC0489 (sequenced)

The test is flexible, attached to a nodule in shipboard photographs ( Fig. 14A, C ). It measures 15.6 mm long and

11.5 mm wide. The overall shape is roughly and asymmetrically ovate, with one side more or less straight, the other side broadly curved, and the end gently rounded ( Fig. 15B ). There is no distinct stalk, but the attached margin is relatively short, about 4.6 mm in width.

The preserved specimen is 730–870 µm thick. The surface is rather uneven and fairly dark greyish brown when viewed in natural light. There is a lighter peripheral fringe that is only obvious in laboratory photographs of the fixed specimen, where it is best developed around the distal end of the test ( Fig. 14D, E ). In some areas, notably near the upper margin, the wall is composed of radiolarian shells with sponge spicule fragments also visible, leaving substantial gaps between these particles ( Fig. 14E ). Elsewhere, the gaps are largely filled in by much finer material. A few larger agglutinated foraminifera are also incorporated into the structure. The wall is pervaded and held together by a meshwork of fine proteinaceous fibres (linellae). Gaps in the surface are criss-crossed by linellae, through which dark grey stercomare masses are visible. The linellae are particularly well-developed and obvious in the peripheral zone.

The test interior was not examined, but the darker appearance of the test away from the lighter peripheral zone clearly results from the presence of stercomare masses. A row of eight more or less straight, slightly radiating granellare strands were visible at the distal end of the test, immediately inside the peripheral zone, before most were removed for genetic analysis ( Fig. 14D, E ). One of the strands branched once, but the others were unbranched. They were 88–117 µm wide, in some cases expanding to ~145–175 µm at their outer end. The granellare strands that had been removed for sequencing measured 76–190 µm wide ( Fig. 14F ).

RC0608 (not sequenced)

Shipboard photographs show the test bent over from what, presumably, was an upright orientation on the seafloor ( Fig. 15A, B ). It is considerably larger than RC0489, measuring 30.6 mm long with a maximum width of 21.4 mm. The shape is asymmetrically oval ( Fig. 15A, C ), similar to that of the sequenced specimen, although with a short wide proximal stem 7.8 mm wide and ~ 4 mm long that merges with the upper part of the test ( Fig. 15D ).

The preserved specimen is 520–650 µm thick. The test surface has a vague pattern of concentric arcuate zones running parallel to the curved upper (distal) margin ( Fig. 15C ). The wall is very similar to that of the sequenced specimen. Apart from a single agglutinated foraminiferan (Reophax sp.), it is composed largely of radiolarian shells of different sizes and a subordinate proportion of sponge spicules, with a patchy matrix of fine particles occupying the gaps across some parts of the surface ( Fig. 15F ). The meshwork of linellae that holds together the surface layer is strongly developed and clearly visible where there are gaps between the radiolarians and near the margin ( Fig. 15E ). The stercomare can also be seen through these gaps. In more central parts of the test, it forms an interconnected system of irregularly shaped lumps merging into more linear strands that radiate towards the towards the curved upper (distal) margin.

Molecular characterisation. Stannophyllum aff. granularium branches next to S. zonarium (100% BV). The barcoding fragment of the 18S gene of S. aff. granularium is 927 nucleotides long and its GC content is 29%. The two sequences obtained for this species are identical.

Remarks. Three of the 15 Stannophyllum species included by Tendal (1996) in his synoptic checklist of xenophyophores, S. granularium Tendal, 1972 , S. radiolarium Haeckel, 1889 and S. zonarium , have tests composed to some degree of radiolarians (as described by Tendal, 1972). Stannophyllum zonarium , is the most widely reported of all xenophyophores ( Tendal, 1996). The test is clearly zoned and the strongly developed linellae often project from the lower part in tangled bundles ( Tendal, 1972; Gooday et al., 2020a), features are not seen in the species described here. In any case, genetic data indicate that the two species are distinct ( Fig. 1 ).

The other two possible candidates have the following characteristics ( Tendal, 1972). In S. granularium the test is 1.5–3.0 mm thick, dark brown in colour, sometimes with faint zonations, the surface is ‘granular’, the xenophyae comprise a combination of mineral particles and sponge spicules with a varying proportion of radiolarians and the linellae are strongly developed, often as a surface layer. In S. radiolarium, the test is 1–1.5 mm thick, lighter in colour, has a ‘soft consistency’, the surface is ‘smooth’, the xenophyae are mainly radiolarians with occasional sponge spicules, the linellae are sparse and do not form a surface layer.

The three possibly damaged specimens of S. granularium illustrated in Pl. 10A–C of Tendal (1972) and Pl. 1.3–1.5 of Tendal (1973) do not closely resemble either of our specimens. Tendal’s (1972) descriptions, however, suggest that our specimens are closer to S. granularium than to S. radiolarium, although there are differences. Radiolarians are generally a subordinate, rather than dominant, component of the xenophyae in S. granularium and may be almost absent. Our specimens are much thinner (<1.0 mm when preserved, compared to 1.5–3.0 mm). With the exception of an anomalous record from the Indonesian region (Banda Sea, 4365 m depth), all specimens of S. granularium come from ~ 5000–6700 m in the NW Pacific (32–54˚ N), some distance from our shallower sampling area in the eastern equatorial Pacific. For these reasons, we cannot confidently assign our specimens to Tendal’s species, but refer it instead to Stannophyllum aff. granularium .

Figures

FIGURE 1. PhyML phylogenetic tree based on the 3'end fragment of the SSU rRNA gene, showing the evolutionary relationships of 79 foraminiferal sequences belonging to monothalamids. Specimens marked in bold indicate those for which sequences were acquired during the present study. The tree is unrooted. Specimens are identified by their accession numbers. Numbers at nodes indicate bootstrap values (BVs). Only BVs>70% are shown.

FIGURE 14. Stanophyllum aff. granulatum; sequenced specimen RC0489 (BC010). A, B Shipboard photographs A, Specimen attached to a nodule. B. Side view. C–F, Laboratory photographs. C, Entire specimen. D, E, Edge of test showing granellare branches and fringe of radiolarians attached to organic fibres (linellae). F, Granellare removed from test.

FIGURE 15. Stanophyllum aff.granulatum; specimen that was not sequenced, RC0608 (BC015).A, B,D Shipboard photographs C, E, F, Laboratory photographs.A, B, Specimen attached to a nodule. C. Specimen detached. D, Base of test showing attachment to nodule. E, Detail of surface. F, Edge of test showing organic fibres (linellae). Scales were not available for A and B.