Sympodium gibbaeum sp. n.

Figs. 3D, E, 8, 9

Material. Madagascar. Holotype: SMNHTAU_ Co _36121, Nose Be (13°29.032’S, 47°58.721’E), 2–14 m, 3 December 2012, coll. Y. Benayahu. Paratypes; SMNHTAU_ Co _ 38227, ten fragments, same details as the holotype, SMNHTAU_ Co _36032, Ankaréa (12°49.978’S, 48°34.504’E), 26–28 m, 30 November 2012, coll. Y. Benayahu.

Description. Encrusting colony with densely packed knob-like mounds (Fig. 8A). The holotype measures 3.2 x 1.5 cm, the mounds are 8–10 mm high and the spreading membrane in between is about 1 mm thick. The polyps are uniformly spaced throughout the surface of the colony; those of the upper part of the mounds are fully retracted, leaving distinct round pits of about 1 mm in diameter (Fig. 8A). The polyps of the periphery of the lobes are partly expanded, up to 1.2 mm long, with tentacles up to 0.5 mm long. Most of the pinnules are retracted, but there appears to be a single row of 3–5 pinnules on either side of the tentacle.

The sclerites of the holotype are ellipsoid platelets, abundant throughout the colony, and measure 0.014 –0.016 x 0.016 –0.019 mm in diameter (Fig. 9A). They are composed of packed calcite rods whose tips appear to bend over at the surface (Fig. 9B).

Color. The ethanol-preserved colony is light cream.

Etymology. The species’ name, gibbaeum, is derived from the Latin “gibbosus” meaning hunchback, referring to the mounds of the colony.

Variation. The paratype SMNHTAU_Co_38227 (Fig. 8B) resembles the holotype, but is smaller. The paratype SMNHTAU_Co_36032 (Fig. 8C) comprises a delicate membranous colony featuring several low mounds. The spreading membrane is 1–2 mm thick with some individual polyps set apart, leaving 4–10 mm gaps with no polyps but the few low mounds do bear polyps (Fig. 8D). The sclerites of the paratype SMNHTAU_Co_38227 (Fig. 9C) resemble those of the holotype, but their outline can be more angular and their surface microstructure presents an oblique-to-parallel orientation of the calcite rods (Fig. 9B).

Remarks. The morphology of the colonies, featuring mounds, mostly with a round outline, is considered diagnostic for the species. The morphological differences between the holotype (Fig. 9A) and the paratypes (Fig. 9B–D) are suggested to represent intraspecific variation. The ethanol-preserved holotype (SMNHTAU_Co_36121) and a paratype (SMNHTAU_Co_36032) were sequenced and subsequently assigned to MOTU46 (McFadden et al. 2019).

Living features. The live colonies feature distinct mounds with expanded polyps, also presenting some color variation such as green-beige or gray (Fig. 3D, E).

Distribution. Madagascar.