Sympodium yonaguniensis sp. n.

Fig. 14D, Fig. 17, Fig. 18

Material. Japan. Holotype. SMNHTAU_ Co _35117, Ryukyu Archipelago, Yonaguni Is., Umabanazaki Point, 8–12 m, 3 July, 2010, Coll. Y. Benayahu ; Paratypes. SMNHTAU_ Co _38228, same details, 11 fragments, SMNHTAU_ Co _35164 Ryukyu Archipelago, Yonaguni Is., West Point, 16–22 m, 5 July, 2010, 6 fragments, Coll. Y. Benayahu ; Taiwan. SMNHTAU_ Co _35754 Green Is. Iron Artificial Reef (22°38’33”N, 121°28’31”E), 20–26 m, 5 September 2012 .

Description. The holotype is an encrusting and soft colony with irregular upper surface, measuring 5 x 32 mm and up to 3 mm thick (Fig. 17A). Some polyps emerge individually and others in small groups of 3–5, forming low mounds up to 2–4 mm in diameter. Almost all the polyps are retracted and the few that are either partly or mostly expanded measure up to 2 mm, with tentacles up to 1 mm long. Most of the pinnules are retracted and only the few partly retracted ones can be seen under the dissecting microscope.

The sclerites of the holotype are ellipsoid platelets, abundant throughout the colony, measuring 0.012 –0.016 x 0.010 –0.012 mm in diameter (Fig. 18A). They are composed of densely packed calcite rods whose tips provide a granular appearance to the sclerite surface (Fig. 18B).

Color. The ethanol-preserved colony is light cream.

Living features. The live colonies present clusters of brown-gray expanded polyps over the reef substrate (Fig. 14D).

Etymology. The species is named after Yonaguni Island, the type locality of the species.

Variation. The paratypes SMNHTAU_Co_38228 (Fig, 17B), SMNHTAU_Co_35164 and SMNHTAU_Co_ 35754 (Figs. 17C, D), are smaller than the holotype, but otherwise resemble the holotype.

Remarks. The morphological features of the colony, specifically the relatively thick encrusting membrane and the polyps emerging in groups from low mounds, are considered to be diagnostic for this species. The ethanol-preserved holotype and paratypes (SMNHTAU_Co_35164, SMNHTAU_Co_35754) were sequenced and subsequently assigned to MOTU36 (McFadden et al. 2019).

Distribution. Japan: Ryukyu Archipelago, Yonaguni Island; Taiwan: Green Island.