Clathrina rodriguesensis sp.nov.

Figures 24a–e, 25a–g, 26a–d, 27a–d

Material examined. Holotype, RMNH Por. 11694, Mauritius, Rodrigues, Mourouk Ebony, Castel Rock, 19.7648°S 63.4626°E, depth 12 m, scuba, coll. N.J. de Voogd, field nr. ROG108, 19 October 2016.

Paratypes, RMNH Por. 11624, Mauritius, Rodrigues, Passe Baladirou, 19.6683°S 63.46307°E, depth 12 m, scuba, coll. N.J. de Voogd, field nr. ROG025, 16 October 2016 ; RMNH Por. 11662, Mauritius, Rodrigues, Passe Baladirou, 19.6683°S 63.46307°E, depth 12 m, scuba, coll. N.J. de Voogd, field nr. ROG069, 18 October 2016 ; RMNH Por. 11670, Mauritius, Rodrigues, Passe Baladirou, 19.6683°S 63.46307°E, depth 12 m, scuba, coll. N.J. de Voogd, field nr. ROG077, 18 October 2016 ; RMNH Por. 11671, Mauritius, Rodrigues, Passe Baladirou, 19.6683°S 63.46307°E, depth 12 m, scuba, coll. N.J. de Voogd, field nr. ROG078, 18 October 2016 ; RMNH Por. 11705, Mauritius, Rodrigues, Passe Baladirou, 19.6683°S 63.46307°E, depth 8 m, scuba, coll. N.J. de Voogd, field nr. ROG119, 20 October 2016 ; RMNH Por. 11710, Mauritius, Rodrigues, Passe Saint François, 19.69893°S 63.5005°E, depth 15 m, scuba, coll. N.J. de Voogd, field nr. ROG124, 20 October 2016 .

Additional specimens. ZMA Por. 11282, Seychelles, Amirantes, Desroches Atoll, SW rim, 5.7167°S 53.6167°E, depth 5–30 m, scuba, coll. M.J. de Kluijver, field nr . NIOP-E stat. 774/01, 30 December 1992; ZMA Por. 12096, Seychelles, Amirantes, St. François Atoll, Île Bijoutier, 7.0833°S 52.7333°E, reef, outer slope, depth 6–18 m, scuba, coll. R.W.M. van Soest, field nr . NIOP-E stat. 792/12, 5 January 1993.

Description. In situ, the species forms a massively encrusting cormus (Figs 21a–d, 22a–b) consisting of relatively wide tubuli (approximately up to 2–3 mm in diameter), which are nevertheless closely anastomosed, showing little differentiation in tubule-width. The cormus may be also flatly encrusting over a larger area (Fig. 23a) with loosely anastomosing tubuli showing a tendency to be arranged ladder-like, with longitudinal main tubuli and interconnecting secondary thinner tubuli. The main tubuli frequently end in an oscule, often slightly erected above the cormus (Figs 22a–b). Lateral size considerable, 20 x 15 cm or more, thickness 1–4 cm. Color white with blueish or greyish tinges in situ, white or pink ‘on deck’ (Figs 21b, 22c,e, 23b), in preservation they become pale beige (Figs 21c, 22f: Rodrigues specimens) or brown (Fig. 24a: Seychelles specimens). The latter have possibly become brown by exposure to algae or other sponges, as their in situ color was noted as blueish white. Size of preserved fragments up to 10 x 5 x 4 cm. Consistency firm.

Aquiferous system. Asconoid.

Skeleton. Tubule walls multi-layered, densely crowded in most specimens (Figs 21d, 22d, 23c), but less dense in one of the Seychelles specimens (Fig. 24b).

Spicules. (Figs 21e, 22g, 23d, 24c–d). Triactines only, but occasional fragments of trichoxea-like spicules were observed (not shown).

Triactines, robust, with conical actines, measuring 97– 169 –225 x 11 – 18.2 –22 µm in the Rodrigues specimens. The two Seychelles specimens which we believe to belong to this species have actines respectively 93– 159 –198 x 11 – 17.4 –21 µm (ZMA Por. 11282) and 111– 164 –204 x 13 – 17.8 –21 µm (ZMA Por. 12096) (Figs 24c–d). The actines in all these specimens are conical

Distribution and ecology. Rodrigues, Seychelles, on reefs, 5–30 m depth.

Etymology. The name refers to the type locality, the island of Rodrigues, east of Mauritius.

Remarks. We provide ample illustrations of this new species to demonstrate the habitus variability. Spicules are closely similar in all above-mentioned specimens.

Partial 28S sequences of seven specimens collected at Rodrigues and two Seychelles specimens grouped in a separate clade (cf. Fig. 2A) at high bootstrap value, apparently not closely related to the other Western Indian Ocean Clathrina .

Australian and Indonesian Clathrina heronensis Wörheide & Hooper, 1999 is close in color and spicule size and shape, but its habitus is flatly encrusting and it has thinner tubuli (1 mm) than the present material. An Indonesian specimen identified as C. heronensis was sequenced and found to share a clade with lower bootstrap value with the present material in the molecular tree of Fig. 2A. A separate analysis of the sequences of both species in a trimmed alignment with length of 395 sites showed a difference of eight sites between C. heronensis and C. rodriguesensis sp.nov.