Figs. 1, 2, 3, 4
Material examined. Holotype: MNHN-IK. 2009 - 834 Balhaf, Yemen (13 ° 58.228 ’ N; 48 ° 10.759 ’ E), 5 m, coll. F. Benzoni & M. Pichon, 20 /09/ 2007, collection code BAL085.
Paratypes: MSNM COE 332 Al Mukallah (14 ° 31.059 ’ N; 49 ° 10.283 ’ E), 3.5 m coll. M. Pichon & F. Benzoni, 17 /03/ 2007, collection code MU003; UNIMIB Y 359 Balhaf (13 ° 58.163 ’ N; 48 ° 10.928 ’ E), 4 m, coll. F. Benzoni, 08/09/05 (GenBank accession number HE 585991).
Other material: Yemen Red Sea UNIMIB KA022 Kamaran Island (15 ° 21.988 ’ N; 42 ° 37.540 ’ E) F. Benzoni & A. Caragnano, 28 /09/ 2009; KA 170 Al Badi' (15 ° 29.573 ’; 42 ° 32.109 ’ E) 02/ 10 / 2009; Djibouti TO-DJ030, Ras Ali, Gulf of Tadjoura, (11 ° 46.354 ’ N; 42 ° 57.286 ’ E), 7 m, coll. F. Benzoni, 28 /01/ 2010; TO-DJ079, Oblal, Gulf of Tadjoura, (11 ° 48.677 ’ N; 43 ° 3.427 ’ E), 8 m, coll. F. Benzoni, 29 /01/ 2010; TO-DJ 134, Musha, Gulf of Tadjoura, (11 ° 44.623 ’ N; 43 ° 10.116 ’ E), 10 m, coll. F. Benzoni, 31 /01/ 2010; Ye m e n G u lf o f Ade n UNIMIB Y 358 Balhaf (13 ° 58.163 ’ N; 48 ° 10.928 ’ E) coll. F. Benzoni, 08/09/05 (GenBank accession number HE 585990); Y 360 Balhaf (13 ° 58.163 ’ N; 48 ° 10.928 ’ E) coll. F. Benzoni, 08/04/06 (GenBank accession number HE 585992); Y 694 Balhaf (13 ° 58.402 ’ N; 48 ° 12.410 ’ E) coll. F. Benzoni, 10 /03/08; BAL015 Balhaf (13 ° 58.331 ’ N; 48 ° 11.164 ’ E) coll. M. Pichon & F. Benzoni, 04/03/ 2007; BAL042 (13 ° 58.865 ’ N; 48 ° 10.611 ’ E) coll. F. Benzoni 20 /05/ 2007; BAL044 (13 ° 58.865 ’ N; 48 ° 10.611 ’ E) coll. M. Pichon & F. Benzoni 16 /09/ 2007; BAL069 Balhaf (13 ° 58.228 ’ N; 48 ° 10.759 ’ E) coll. M. Pichon & F. Benzoni, 20 /09/ 2007; BAL 108 Balhaf (13 ° 58.228 ’ N; 48 ° 10.759 ’ E) coll. M. Pichon & F. Benzoni, 20 /09/ 2007; BAL 175 b Balhaf (13 ° 58.163 ’ N; 48 ° 10.928 ’ E) coll. M. Pichon & F. Benzoni, 22 /09/ 2007; BAL 250 Balhaf (13 ° 58.444 ’ N; 48 ° 11.560 ’ E) coll. M. Pichon & F. Benzoni, 23 /09/ 2007; MU027 Al Mukallah (14 ° 31.059 ’ N; 49 ° 10.283 ’ E) coll. M. Pichon, F. Benzoni & C. Riva, 17 /03/ 2007; MU091 Al Mukallah (14 ° 30.923 N; 49 ° 9.254 E) coll. M. Pichon & F. Benzoni, 17 /03/ 2007; BA092 Sikha Island (13 ° 55,775 N; 48 ° 23,219 E) 8 m, coll. F. Benzoni & S. Montano, 21 / 11 / 2008 (GenBank accession number HE 585993); Socotra Island UNIMIB SO057 Araher (12 ° 34.942 ’ N; 54 ° 26.004 ’ E), 18 m, coll. F. Benzoni & A. Caragnano, 13 /03/ 2010; SO 114 Ras Qadamah (12 ° 41.902 ’ N; 53 ° 39.682 ’ E) 10 m, coll. F. Benzoni & A. Caragnano 17 /03/ 2010; SMF (housed at EPA Socotra) C 90 S, ST- 145 W Ras Momi, 02/04/ 1999; C 325 S, ST- 738 Medina, 18 /04/ 2000.
Skeletal characteristics of the holotype. The holotype (Fig. 1) is part of a large colony (Fig. 1 a). The fragment is 9 cm long, 4.5 cm wide, and 2.5 cm thick. It is characterized by an encrusting base from which three taller digitations and one shorter digitiform non-anastomosing projections develop. Digitations tips are rounded (Fig. 1 A–C). Corallite density over the corallum surface is 50–66 corallites/cm 2 (Fig. 1 C–D). Corallites are flush with the coenosteum, although they tend be slightly sunken at the base of the digitations. They are separated by coarsely ornamented coenosteum and can be locally arranged in short series 3 to 6 corallites long (Fig. 1 D). Collines, or ridges, are not present. Calice diameter ranges from 0.9 to 1 mm. A columella is absent. The typical septa arrangement of the genus Porites is observed with 12 septa arranged in four lateral pairs, one dorsal septum and three ventral septa (Fig. 1 E; Fig. 2 A–B). The dorsal septum is shorter than other septa (larger arrows in Fig. 2 B) and the synapticulae connecting it to one of the two lateral pairs, or both, can be more or less visible from the top (smaller arrows in Fig. 2 B). The ventral triplet is fused (Fig. 2 B). Five large pali are normally present in corallites, four in front of the four lateral pairs of septa, and one in front of the ventral triplet (Fig. 2 B). No palus is found in front of the short dorsal septum. Upper septal margins carry 1 finely ornamented denticle (Fig. 2). The innermost circle of synapticulae connecting the pali is visible and can be thin (Fig. 2 A–C) or thick (Fig. 2 D–F). In some corallites it can be so thick to resemble a hollow columellar structure (Fig. 2 E–F). In these corallites an irregular fusion of the ventral triplet can be observed (Fig. 2 F), and two smaller pali or no palus at all can be found in front of it.
Variability. The study of the type series and of the other collected specimens showed that although a digitate colony developing from an encrusting base is typical of Porites fontanesii sp. nov., a certain degree of variability of the digitations upper ends diameter and shape is observed. These can be circular to oval in section (Fig. 4) with thickness ranging from 1 to 4 cm. In larger colonies digitations tend to fan out and occasionally branch (Fig. 3 A–D, Fig. 4 C–G). Corallite organization over the colony surface is the same as the type material throughout the whole collection. However, although corallites are generally flush with the coenosteum, in certain specimens they can be more sunken in certain parts of the corallum, typically towards the base of the digitations. At the corallite level, calice diameter, septal plan, and number of pali and denticles are consistent with the type series. In some specimens the denticles can be more visible (Fig. 4 J) than in others (Fig. 4 D). When this happens, the small corallites are more easily visible to the naked eye and attain a flower-like appearance (Fig. 4 J). The character showing the highest within and between specimens variability is the thickness of the innermost cycle of synapticulae (Fig. 2). When the synapticulae connecting proximal ends of the septa are thicker the species typical pattern of septal fusion can be less easily visible (Fig. 2 D–F).
Field characteristics and identification. Porites fontanesii sp. nov. forms colonies ranging from a few centimeters to 50 cm in diameter and is found between 5 and 15 m depth. The corallum base is usually encrusting and from it digitations of variable thickness and height develop (Fig. 3 A–D). In larger colonies branching can be observed. Digitations and branches tend to fan out (Fig. 3 A–D). Polyps are usually extended during the day (Fig. 3 D, F). When these are retracted the smooth surface of the corallum (Fig 3 E) and the corallites separated by the coenosteum (Fig 3 G) are visible. Colour ranges from grey or pale beige to light brown, and polyps are typically extended during the day. (Fig. 3 C–D).
Etymology. This species is named after Prof. Marcello Fontanesi, Magnifico Rettore of the University of Milano-Bicocca.
Distribution and frequency. P. fontanesii sp. nov. has been recorded from the southern Red Sea, the Gulf of Tadjoura, the Gulf of Aden and the north-western Indian Ocean (Fig. 5). Southern Red Sea (Yemen) Kamaran Island, Kutama, Tiqfash, Uqban, Al Badi, Gulf of Tadjoura (Djibouti) Tadjoura, Obock, Musha Island, Northern Gulf of Aden (Yemen) Aden, Balhaf, Bir Ali, Sikha Island, Burum, Al Mukallah, and from Socotra Island. No additional records from published illustrations or museum specimens have been found so far.
Porites fontanesii sp. nov. was most frequently observed in the Yemen Red Sea islands (Fig. 6) where it was observed in 88 % of the sampled sites (n = 16). It was also frequently observed along the Gulf of Aden coast of Yemen at Aden (60 %, n = 5), Balhaf-Bir Ali (72 %, n = 32) and Burum-Mukallah (67 %, n = 18). Finally, the species was recorded at 20 % and 11 % of the sites in Djibouti (n = 27) and Socotra (n = 15), respectively.
Phylogenetic analysis. A total of 48 sequences were aligned and subjected to phylogenetic analysis. Overall, 572 positions (194 showing gaps) characterized the alignment after excluding two hypervariable and unaligneable regions (about 200 bp in total, situated at the beginning of ITS 1 and at the end of ITS 2). Among 85 variable sites, 69 were parsimony informative, while a GTR+G+I evolutionary models was selected as the most appropriate fro the data by AIC.
The phylogenetic trees obtained according to the two different criteria showed concordant topologies (Fig. 7). Two main clades were found, one relating to Central American Porites species, (subclades X, XI and XII sensu Forsman et al. 2009) and the other, a large, polytomic clade including both Atlantic and Pacific species (subclades IX, VIII, VII, VI, V, III, II, I sensu Forsman et al. 2009). In both cases, the internal relationships agreed with the phylogeny obtained by Forsman et al. (2009) from which the sequences were taken. Specimens of Porites fontanesii sp. nov. are found in a subclade basal to, and well divergent from, the second main clade. A mean value of 6.4 % (± 1.3 s.d.) p-distance separates P. fontanesii sp. nov. from the other species of the genus. Internal divergence within P. fontanesii sp. nov. is one order of magnitude lower (0.5 % ± 0.3 s.d).
Bayesian analysis performed with the software BEAST showed signals of convergence to the stationary distributions of parameters after 10.000.0 0 0 generations, since all ESS were largely> 200 and parameters distribution were smooth. The analysis was repeated three times obtaining the same inferences. An evolutionary pattern congruent with a molecular clock was not rejected (ucld.stdev = 0.3, 95 % HPD 0.0– 0.6) and a mean rate of 2.4 x 10 - 2 (95 % HPD 1.3 x 10 - 2 –3.7 x 10 - 2) subst/site*My was estimated. On these basis, the main divergence between P. fontanesii sp. nov. and the other polytomic clade is dated at 8.53 MYA (95 % HPD 4.0–14.0 MYA), thus indicating a likely late Miocene origin of this species.