Holotype: MNHN-IK.2012-8000 (Figures 2–4). Type Locality: Taravai Island, Gambier, French Polynesia (MV Tara, Tara Oceans Expedition, Site 9), 23°9.404'N, 135°1.769'E, 10 m, 30 June 2011, coll. F. Benzoni.

Corallum: The holotype is a knob-shaped, plocoid, encrusting colony attached to a fragment of a dead tabular Acropora coral (Figure 2). The specimen is 9.2 cm high, and 8.5 x 5 cm wide at the base in its original growth position.

Corallites: The 12 corallites are oval in shape and variable in size (Figure 2, 3), ranging from 3.3 cm in diameter (C1 in Figure 2, 3a) to 1.0 cm. Corallites are organically united (see terminology in Budd et al. 2012). The central position of C1 (the largest corallite) is less obvious in the holotypes due to its knob-shaped growth form. Corallites protrude up to 1 cm and are directed in different directions (Figure 2). Corallite wall is septothecal.

Costosepta: Variable in number depending on the size of the corallite (Figure 3a–d), exsert and thickened over the theca. The largest corallite contains 26 septa arranged in five orders (Figure 3a). Septa of the first three orders are thicker than the others. Septal teeth are elliptical in outline, large and high (> 0.6 mm) according to the parameters defined by Budd et al. (2012) (Figure 3a–d), and their tips are irregular bulbous. Tooth spacing is very high (> 2 mm). Septal side granulation is weak. Paliform lobes (see Benzoni et al. 2011 for a definition) thick and well developed, forming an obvious crown around the columella, which was also visible in vivo. Paliform lobes always present and of similar size at the proximal margin of the first two orders of septa (Figures 3a–d). In larger corallites, in which more than four orders are present, they can also form in front of the third order but then they are of smaller dimensions (Figure 3b). The costal parts of the costosepta are thick and unequal. They are strongly ornamented by triangular shaped teeth (Figure 3e, f), which bear fine granules on the tip (Figure 3f). Exothecal alveoli are present at the insertion of lower order costae (Figure 3e). Costae cover the whole surface of the coenosteum between corallites.

Columella: Well developed, deep in the fossa (Figure 3b) made by a mesh of twisted intermingled processes derived from the inner end of the higher order septa: the first two in smaller corallites (Figure 3a–d), and up to the fourth order in larger corallites (Figure 10b–d).

Colour: The living colony was mottled brown. Tips of septa and costae ornamentation varied from light beige to white.

(Gambier, French Polynesia, Tara Oceans Expedition): UNIMIB TO-GA028, Akamaru Island (Site 2), 23°11.082'N, 134°54.331'E, 26 June 2011, coll. F. Benzoni; UNIMIB TO-GA071 Makaroa Island (Site 6), 23°12.960'N, 134°57.991'E, 28 June 2011, coll. F. Benzoni; UNIMIB TO-GA099 Taravai Island (Site 11), 23°9.540'N, 135°3.055'E, 1 July 2011, coll. F. Benzoni; UNIMIB TO-GA186 Taravai Island (Site 9), 23°9.404'N, 135°1.769'E, 30 June 2011, coll F. Benzoni.

Variation of skeletal structures: Colony size is relatively small (Figures 2–8), the largest colony is 20 cm wide (Figure 6f). Corallum generally encrusting, its plane following the surface of the underlying substrate (Figures 4b, d, e) but also knob-like (Figures 4a, c) with foliose margins where they become detached from the substrate. The number of corallites per colony is low, ranging from 1 to 15. A large, central primary corallite is always present (Figures 2, 6a, b). Secondary corallites are often inclined in various directions and show variable diameter sizes within the same colony (Figures 5a–e, Table 1). The largest corallite observed (specimen UNIMIB TO-GA099, Figure 4d) is 3.5 cm in diameter, the smallest, in the same specimen, 0.9 mm (Figure 5e). The numbers of septa, orders of septa, and paliform lobes vary between and within colonies. First order septa always thicker than the others and in some cases up to 4 mm thick (Figure 5f). Columella always present, large and oval in the largest corallite, less developed is smaller corallites. Costae typically thick, alternating in size (Figure 5c, d) and strongly dentate, although variably so between specimens.

Field characteristics and colouration: The colouration is showing much variation, ranging from dark brown (Figures 7a–c, e), to mottled brown (Figures 2a, 7f), beige (Figures 6e, f), and bright green (Figures 6c, 7d). The tissue on the tips of septal teeth and costal spines teeth can be lighter in colour (Figure 6c) or white (Figure 7c), possibly as a result of tissue being less thick above these structures. In very mottled colonies (Figure 7f) or with lighter colouration of the tissue over costoseptal teeth (Figure 7b) the size and shape of the corallites may be hard to detect. The crown of paliform lobes is always prominent (Figure 5) and often obvious, especially in the largest corallite (Figures 6, 7b).

Ecology: Echinophyllia tarae sp. n. inhabits protected reef habitats and was observed between 5 and 20 m depth. It commonly grows on dead coral fragments, usually parts of branching or tabular Acropora colonies, which are covered by crustose coralline algae and fleshy macroalgae (Figures 6–7). This species can grow on well-illuminated surfaces but also encrusts shaded underhangs. In well-lit conditions the appearance is typically corrugated (Figures 6a–b, e–f, 7a–d). However, in some cases a certain degree of inflation of the soft tissues was observed (Figures 6a–b, f), although this generally depends on the very developed ornamentation of the underlying costosepta, which is most obvious when a live colony (Figure 6f) is compared with the clean skeleton (Figures 4b, 5d). In poorly lit conditions the overall appearance is smoother and the colouration more uniform (e.g. Figures 6d, 7e–f) although the oral discs remain generally brightly coloured and different from the rest of the tissues. Re-growth of partially dead colonies, especially at the margins, is common (Figure 8). Such patters of partial death and recovery could result from competition with other benthic invertebrates, like soft-bodied corallimorpharians and zoanthids which can co-occurr with this species (Figure 8a). The observed patterns of partial death may also be caused by deposition of sediment on the living corals. In fact, Echinophyllia tarae sp. n. is most commonly found at sheltered sites characterized by calm water conditions and muddy sediment which could be stirred up and deposit on benthic organisms suffocating them (Erftemeijer et al. 2012). The dead parts of the corallum are generally encrusted by coralline algae over which the coral can re-grow or re-settle (Figure 8b).

Occurrence:This species was commonly encountered on the fringing reefs off Mangareva, Aukena, Tekava, Akamaru, Kamaka, Makaroa, Agakauitai, and Taravai islands as well as at the base of the lagoon pinnacles found in the lagoon north of Mangareva Island (Figure 1, Table 2). Its distribution outside the Gambier archipelago is unknown although it could also occur in the Austral Islands (see Discussion section). No record is known from other localities.

Affinities:In its encrusting growth form, and in the presence of a central larger and protruding corallite this species is similar to Echinophyllia echinata and Echinomorpha nishihirai (see Discussion). Ongoing molecular analyses will reveal the phylogenetic relationships of this species with its congeners.

This species is named after MV Tara, which allowed the exploration of coral reefs in Gambier. Moreover, the name “tara” in the Polynesian language may refer to a spiny, pointed object, which applies well to the new species typically featuring pointed skeletal structures. In the same language, Tara is also the name of a sea goddess.