Holotype: PMBC 11860, Koh Doc Mai, Thailand, 07°47.76'N, 98°32.09'E, depth 8 meters, 26 September 2007 (1 colony), M. P. Janes collector. Paratypes: PMBC 11861, Koh Phi Phi, Hin Bida, Thailand, 07°39.20'N, 98°45.83'E, depth 10 meters, 28 September 2007 (1 colony), M. P. Janes collector. PMBC 11862, same data as the holotype.

The holotype is comprised of multiple short, branched stalks sharing a common base attached to coral rock. In life, the holotype (Fig. 1a) is thickly beset with monomorphic polyps which were observed to be non-pulsatile. The tentacles are cylindrical, slender and up to 2.0 cm long (Fig. 1b). In a preserved state, the holotype consists of multiple stalks; two of the stalks are divided into two short branches (Fig. 2a). The stalks measure up to 8.0 mm tall and 5.0 mm wide at the base. A slightly convex capitulum is present at the distal end of the stalks from which moderately dense aggregations of polyps are growing. The polyp bodies are cylindrical, shrunken and measuring from their attachment at the capitulum to the base of the tentacle they are 1.5 mm long by 0.5 mm wide. Tentacles are slender, measuring up to 8.0 mm long by 0.2 mm wide with a blunt tip. There is one row of pinnules present on either side of the tentacle (Fig. 2b at arrow) with 17 to 19 pinnules in a row. The pinnules are barrel-like with a rounded tip and slight taper at the end. They measure 0.2 to 0.3 mm long by 0.1 mm wide. There is an open space on the tentacles between adjacent pinnules measuring 0.1 to 0.15 mm wide, nearly equal to their width. Zooxanthellate.

Sclerites are present in all parts of the holotype. They are moderately dense in the polyps (Fig. 3a–b) and fewer are found in the basal portion of the stalk. All of the sclerites are round to slightly oval or irregularly shaped spheroids (Fig. 4a). They measure from 0.010 to 0.018 mm in diameter on average with a few sclerites as large as 0.020 mm in maximal diameter and the smallest recorded at 0.005 mm in diameter. The sclerites are comprised of numerous, minute circular to egg-shaped corpuscular microscleres that quickly disassociate when extracted from the coral tissue with sodium hypochlorite. Rarely, a second form of sclerite can be found in the polyp tissue, which contains a solid calcite core coated with microscleres (Fig. 4b). The microscleres measure from 0.00035 to 0.00060 mm in diameter. SEM imaging revealed that they have a fine, granular surface ultrastructure (Fig. 4c) when viewed under moderately high magnification (×40, 000). The ultrastructure of the surface is comprised of a series of ridges, furrows, and coarse nodules (Fig. 4d) when examined at 65, 000 power. Most microscleres are intact but occasionally fractured ones are found (Fig. 4e). Broken microscleres reveal the presence of a cavity or cavities within. Further evidence of these can be seen in FIB imaging where the microsclere has been sliced longitudinally, demonstrating the depth of the furrows (Fig. 5a) and size of cavities (Fig. 5b) when magnified at 200, 000 power.

The preserved specimens are cream colored with whitish tentacles and light tan pinnules. Living colonies exhibit tan colored stalks; white polyp bodies and tentacles, and pinkish pinnules (Fig. 1a–d).

The name is derived from the collection location, the Andaman Sea.

This species was collected from Koh Doc Mai (Fig. 6) and Koh Phi Phi, Hin Bida located along the eastern coast of Phuket Island, Thailand. Colonies occur in low abundance, spaced 1-2 meters apart on small ledges of vertical walls growing among sea fans, corallimorpharians, and Dendronephthya sp. soft corals. Ovabunda andamanensis sp. n. has also been observed in situ in the Mergui Archipelago, Myanmar (T. Chanmethakul, personal observation).

Both the holotype (PMBC 11860) and one paratype (PMBC 11861) were very similar in size (up to 7.0 cm in life), sclerite dimensions, exhibited non-pulsatile polyps, pinnule rows and number of pinnules per row. The other paratype (PMBC 11862) was smaller in life (Figs 1c, 2c), measuring up to 5.0 cm tall and exhibited tentacles that curved inward (Fig. 1d). It differed from the holotype in having shorter tentacles and two rows of 13–14 pinnules in each row (Fig. 2d) instead of one row with 17–19 pinnules.

In comparing the morphology of Ovabunda andamanensis sp. n. to nominal Ovabunda species colony size, sclerite size and shape, and pinnule arrangement were examined, with the later considered a more variable diagnostic character. Among species of Ovabunda described as having one or two rows of pinnules, O. arabica, O. biseriata, O. gohari, O. faraunensis and Ovabunda verseveldti most closely resemble Ovabunda andamanensis sp. n. Ovabunda gohari and Ovabunda verseveldti are similar to the holotype in having primarily one row of pinnules although occasionally two rows are present in polyps of Ovabunda gohari. The overall range of sclerite sizes is larger in Ovabunda gohari, 0.033–0.063 mm, compared to the 0.010–0.018 mm in Ovabunda andamanensis sp. n., there are 18–22 pinnules in a row compared to 17–19 pinnules in Ovabunda andamanensis sp. n., and Ovabunda gohari has pinnules spaced at 2–3 times the pinnule width along the tentacles whereas in Ovabunda andamanensis sp. n. pinnules are more closely set. According to Reinicke (1997: 31) Ovabunda gohari sclerites are “… packed between polyp bases and in the syndete’s wall between mesenteries, giving a longitudinal whitish banding”; this feature was not observed in the Thailand material. Ovabunda verseveldti contains much larger sclerites (up to 0.030 × 0.049 mm) than were found in Ovabunda andamanensis sp. n. and the pinnules are “densely set in each row, almost touching each other” (Halász et al. 2013) compared to the wider pinnule spacing in the Thailand specimens.

The pinnule number in Ovabunda faraunensis agrees well with the 17–19 pinnules observed in the holotype of Ovabunda andamanensis sp. n., however Ovabunda faraunensis has larger sclerites (Reinicke 1997: 35). The sclerite sizes in Ovabunda arabica 0.028–0.036 mm (Halász et al. 2013), Ovabunda biseriata 0.018–0.035 mm (Verseveldt and Cohen 1971: 60), 0.029–0.063 mm (Reinicke 1997: 33), and Ovabunda faraunensis 0.028–0.044 mm (Halász et al. 2013) are all notably larger than the average range of 0.010-0.018 mm observed in Ovabunda andamanensis sp. n.

Among species of Xenia, Xenia puerto-galerae Roxas, 1933 most closely resembles Ovabunda andamanensis sp. n. The holotype is described by Roxas (1933) as branched, measuring 20.0 mm tall and 8.0 mm in diameter with polyps comprised of thick tentacles that are proportionately small and “two rows of slender pointed pinnules, fifteen to seventeen in a row”. The tentacles are 8.0 mm long by 1.0 mm wide at the base and pinnules measure 0.7 to 0.8 mm long by 0.2 to 0.3 mm wide. However, in the colony with two rows (PMBC 11862) in Ovabunda andamanensis sp. n., the stalks are smaller, 8.0 mm by 5.0 mm, the tentacles are narrower, 8.0 mm by 0.2 mm, the pinnules are smaller, 0.2 to 0.3 mm by 0.1 mm, and there are fewer pinnules (13 to 14). Most notable are the sclerites, which are described as “thin, oval discs 0.018 mm long and 0.018 to 0.0124 mm wide” in Xenia puerto-galerae compared to the 0.010 to 0.018 mm in diameter sphere shaped sclerites observed in Ovabunda andamanensis sp. n. Unfortunately, the location of the holotype of Xenia puerto-galerae remains unknown so a direct SEM comparison of the sclerites could not be performed.