Sorites orbiculus (Forsskal in Niebuhr, 1775)

Lee, Somin & Lee, Fabrizio Frontalini and Wonchoel, 2024, A new record of larger benthic foraminifera from Jeju Island (South Korea), Journal of Species Research 13 (1), pp. 89-99 : 90-92

Sorites orbiculus (Forsskål in Niebuhr, 1775)

( Plate 1-5 ) ÜĒnjḑșẽệ (ljÿ)

Nautilus orbiculus Forsskål in Niebuhr, 1775: 125.

Sorites orbiculus : Ehrenberg, 1840: pl. 3, fig. 2; Lehmann, 1961: 641, text fig. 36; pl. 8, figs. 1-8; Cheng and Zheng, 1978: 198, text fig. 5; pl. 17, figs. 1-9; pl. 31, figs. 1-3; pl. 32, fig. 1; Hatta and Ujiié, 1992: 80, pl. 17, figs. 5, 6; pl. 18, figs. 5, 6; Hottinger et al., 1993: 72, pl. 83, figs. 1-13; Gudmundsson, 1994: 122, text figs. 32, 35; pl. 5, figs. 1-3; Debenay, 2012: 131; Förderer and Langer, 2018: 70, pl. 31, figs. 12-16.

Sorites marginals : Hayward, 1999: 108, pl. 6, figs. 12, 13.

Material examined. Seomyeo diving point, Seongsan-eup , Seogwipo-si, Jeju Island, Korea, 33°27 ʹ 21.54 ʺ N 126°56 ʹ 3.06 ʺ E, 2 August 2020, by SCUBA diving, collected by Heerin Kim, Jisu Yeom and Wonchoel Lee. Voucher specimen NIBR ID: NIBRPR0000111174 .

Description. Test discoidal, with partially fluted, distorted or slightly wrinkled margin, central proloculus, followed

St. Locality Date Lat.(N) Long.(E) Depth Method

Seomyeo diving point, Seongsan-eup,

★ 2020-08-02 33°27 ʹ 21.54 ʺ 126°56 ʹ 3.06 ʺ 18.3 m SCUBA diving Seogwipo-si , Jeju Is., Korea by flexostyle and then with a few, about five to eight evo- lute planispiral chambers arranged in early stage. Later stage with annular series of small, slightly elongated ovate chamberlets that are symmetrical with respect to the equatorial plane, separated by a median annular passage that appears circular in section, crosswise-oblique stolon system connects chamberlets with two chambers of the preceding series and two chambers of the following series, stolons in a single plane, annular sutures waveshaped due to depressions of lateral walls above the septulum forming septulum-sutures; wall calcareous, porcelaneous, smooth; aperture a single row of ovate openings surrounded by protruding rims and few of openings with eight shaped outline due to shell material, bridge the narrow part of the aperture. Test diameter about 1.3 mm and test thickness about 160 μm .

Remarks. Sorites orbiculus is the type species of the genus Sorites , and there are two congeners: S. marginalis (Lamarck, 1816) and S. variabilis Lacroix, 1940 . Referring to WoRMS (2023), S. duplex ( Carpenter, 1883) , which was originally described as Orbitolites duplex Carpenter, 1833 , is listed as a valid species of Sorites . However, this species has been synonymized with Amphisorus hemprichii by some previous studies including Carpenter (1883), Loeblich and Tappan (1987), Gudmundsson (1994), and Förderer et al. (2018). Sorites duplex can be distinguished from S. orbiculus in that the former has marginal apertures arranged in two series, commonly alternating in position, separated by elevated ridges as Amphisorus , whereas the latter has apertures of ovate or 8-shaped or separated two ovate openings arranged in a row, without separation by elevated ridges.

Sorites orbiculus can be distinguished from S. variabilis morphologically by the apertural rim detail, and they are also genetically separated ( Merkado et al., 2013). According to their study, S. orbiculus has prominent apertural rim, while S. variabilis has faint or no rim around the aperture. Additionally, they can be also separated genetically by using partial SSU rDNA sequences.

Sorites orbiculus is most similar to S. marginalis ; these species have often been misidentified as each oth- er. Accordingly, Gudmundsson (1994) suggested that S. marginalis can be considered an eco-type or variation of S. orbiculus . He pointed out that the morphological characters noted by Lehman (1961) that have been used to distinguish the two species are unclear and sometimes co-occur in the same species, or even in a single individual such as the number of apertural opening in a row (double in S. orbiculus , single in S. marginalis ), number of early planispiral chambers(five to eight in S. orbiculus , 13 in S. marginalis ) and the chamberlet shape (more elongate in S. orbiculus , more ovate in S. marginalis ). Furthermore, a molecular phylogenetic study on superfamily Soritoidea revealed that S. orbiculus and S. marginalis are not clearly separated genetically and these species appear to be variants of one species, so that the morphological criteria for the Sorites species identification need to be revised ( Holzmann et al., 2001). The present examined material has somewhat mixed characteristics of S. orbiculus and S. marginalis in terms of row of peripheral apertures. The apertures are surrounded a by distinct rim, and most of the apertures are single elongate-oval openings, and few are 8-shaped openings. However, other characters, including the number of early planispiral chambers and chamberlet shape, point to S. orbiculus . According to Hottinger et al. (1993) and Gudmundsson (1994), in the early annular stage of S. orbiculus , a single apertural row of a single circular, ovate, or 8-shaped openings may appear, and are retained as far as eighth to fourteenth chamber. Our specimens consist of about nine annular chambers, therefore, represent S. orbiculus in early growth stage. As mentioned above, several studies have provided detailed morphological analysis and molecular phylogeny of Sorites ( Lehmann, 1961; Hottinger et al., 1993; Gudmundsson, 1994; Holzmann et al., 2001) but these are somewhat fragmentary. Therefore, a comprehensive study including all Sorites species is needed to clearly understand Sorites diversity.

Sorites species are known to host dinoflagellate symbionts belonging to Symbiodinium ( Hottinger et al., 1993; Hohenegger, 2011). Additionally, diatom symbiont Nitzschia sp. and Nanofrustulum shiloi were isolated and cultured from living S. orbiculus individuals collected from Sesoko Island ( Japan) by Mayama et al. (2000). In our SEM images, there are some diatoms on the inner wall of the broken chamberlets. Based on the previous studies ( Lehmann, 1961; Hottinger et al., 1993; Saraswati, 2002), S. orbiculus prefers to live attached to the surface of substrate, such as of sea grasses and macroalgae or rocks, very firmly. Such individuals are commonly permanently fixed, and the irregular surface of their substrate affect during growth. Therefore, the test can become much distorted, and the annuli of chamberlets may be somewhat incomplete. These morphological features can be confirmed in the present specimen ( Pl. 1 , figs. A- E; Pl. 2-5 , fig. A). Such ecological feature may also be the reason why few individuals were obtained from the sediment samples in present study. To collect additional Sorites individuals for the further study, including molecular analysis, we need to investigate subtidal rocky habitats rich in macroalgae, seagrasses or corals around Jeju Island.

Distribution. Sorites orbiculus is widely distributed in circumtropical waters of Indo-Pacific, and the range is expanding into some regions of the Mediterranean and the Caribbean Realm ( Langer and Hottinger, 2000; Meriç et al., 2014; Förderer et al., 2018; Oron et al., 2022; WoRMS, 2023). The closest sites to Korea where this species has been reported are Japanese Rukyu Islands in the East China Sea, and Xisha, Zhongsha Islands in the South China Sea ( Cheng and Zheng, 1978; Hatta and Ujiié, 1992). The distribution of S. orbiculus is reported below:

Indo-Pacific: Korea, Xisha Islands, Zhongsha Islands, Ryukyu Islands, Gulf of Aqaba, Red Sea, Tanzania ( Zanzibar), Republic of South Africa, Mozambique, Kenya, Chagos Island, Maldives, Indonesia, Palau, Papua New Guinea, Philippines, Federated States of Micronesia (Chuuk lagoon), Solomon Islands, Australia, New Zealand, New Caledonia, Marshall Islands, Kiribati ( Phoenix Islands, Line Islands), Hawaii, Society Islands, Tuamotu Islands, Pitcairn Islands; Atlantic: Israel (Shikmona), Türkiye (Ayvalık, Antalya, Gulf of Kuşadası), Portugal (Selvagens Islands), Gulf of Gabes, Sicily, Brazil, Gulf of Cariaco, Bahamas, Florida Bay.

Figures

Plate 1. Scanning electron microscope (SEM) images and photomicrographs of Sorites orbiculus(Forsskål in Niebuhr, 1775). A-C. SEM image;A. peripheral, apertural view; B, C. lateral view. Scales=100μm. D, E. photomicrographs of the lateral view. Scales=100 μm.

Plate 2. Scanning electron microscope images of the newly recorded LBF, Sorites orbiculus(Forsskål in Niebuhr, 1775). A. peripheral, apertural view; B-I. close-up of apertures. Scales=100 μm.

Plate 3. Scanning electron microscope images of the newly recorded LBF, Sorites orbiculus(Forsskål in Niebuhr, 1775). A. peripheral, apertural view; B-I. close-up of apertures. The ‘8’ shaped aperture is indicated with * symbol. Scales=100 μm.

Plate 4. Scanning electron microscope images of Sorites orbiculus(Forsskål in Niebuhr, 1775). A. peripheral, apertural view; B-H. closeup of apertural side. The symbol * is indicating the ‘8’ shaped aperture. Scales: 100 μm; I-K. close-up of broken part, some diatoms (white arrowhead) are on the inner surface of chamberlet. Scales=10μm.

Plate 5. Scanning electron microscope images of Sorites orbiculus(Forsskål in Niebuhr, 1775). A. peripheral, apertural view; B-G. closeup of apertural side. Scales=100 μm; H-M. close-up of broken part, some diatoms (white arrowhead) are on the inner surface of chamberlet. Scales=10 μm.