Rhabdammina abyssorum Sars

(Plate 1, fig. 1)

Rhabdammina abyssorum Sars in Carpenter, 1869, p. 60; Goës, 1894, p. 19, pl. 4, figs. 67-68; Cushman, 1910, p. 24, text figs. 8-10; 1918, p. 15, pl. 6, fig. 1; pl. 7, fig. 1; Höglund, 1947, p. 25, pl. 1, fig. 2; Jones, 1994, p. 32, pl. 21, figs. 1-8, 10-13; Zheng and Fu, 2001, p. 220, pl. 113, figs. 3-5.

Material examined. Korea, off southern coast of Jeju, St. 7, 33°00 ʹ 00 ʺ N, 127°00 ʹ 00 ʺ E, 5 Aug 2019, by Smith-McIntyre grab, collected by Nayeon Park and Somin Lee. NIBR ID: NIBRPR0000110833, MFORBK ID: MFORB K00287.

Diagnosis. Test is large, free and consists of a central globular chamber and three radiating straight, tubular chambers with nearly uniform diameter. Three tubular chambers are on the same plane, and their ends are open to form apertures. Sutures are not distinct because of the attached sediment grains on test surface. Wall is agglutinated with fine to coarse sediment particles and surface is rough. Aperture is multiple, simple rounded, at the terminal of each tubular chamber. Test length is about 5 mm including tubular chambers.

Remarks. This species is the type species of the genus Rhabdammina, and this is the first record of the genus in Korea. There are 25 recent species belonging to the genus Rhabdammina, and the present species is quite similar to R. linearis in that it has the central globular chamber with tubular chambers. However, R. linearis has only two tubular chambers extending in opposite directions while R. abyssorum has more than three radiating chambers. According to previous reports, the genus Rhabdammina is related to low temperature and deep water depth. The depth of the type locality of R. abyssorum is 823.5 m (450 fathom) and has been reported from deep waters worldwide: from 130-3220 m in the North Pacific Ocean (Cushman, 1910; Zheng and Fu, 2001), 150-3742 m in the Atlantic Ocean (Cushman, 1918), 48-3171 m in the Laptev Sea (Lukina, 2001), and 71.1- 386 m from the Turkish coasts of the east Aegean Sea (Meriç et al., 2004). The present Korean specimen was collected at a depth of 103 m, which is quite shallow, but within the previously reported distribution depth range. This species can have more than three tubular chambers, and the color and grain size vary depending on the materials composing the test (Brady, 1884; Cushman, 1910; Loeblich and Tappan, 1987). Particularly, referred to Cushman (1910; 1918), the materials composing the test wall depend to the bottom sediment condition, and specimens from shallower depth tend to be composed of coarse sediment grains. The present specimen is composed of relatively coarser particles than those reported in other regions. The shallow water specimen reported from the coast of Japan by Cushman (1910) is also composed of coarse granules.

Distribution. Korea, China, Japan, New Zealand, Sea of Marmara, Bay of Biscay, Aegean Sea, Turkey, Norway, Gulf of Saint Lawrence, United States, Cuba, Laptev Sea.