Leucandra pilula Van & De 2018, sp.nov.

Leucandra pilula sp.nov.

Figs 58a–g, 59a–e

Material examined. Holotype, ZMA Por. 10528, Seychelles, Bird Island, 3.7167°S 55.2167°E, coastal reef at 13 m depth, scuba, coll. W. Kolvoort, field nr. NIOP-E stat. 717/34, 20 December 1992.

Paratypes, ZMA Por. 10379a, Seychelles, Mahé, E coast, N of Moyenne Island, 4.6167°S 55.5167°E, depth 1–7 m, reef, snorkeling, coll. R.W.M. van Soest, field nr. NIOP-E stat. 606, 10 December 1992; ZMA Por. 10641 (2 specimens), Seychelles, Amirantes, St. François Atoll, Île Bijoutier, depth 3 m, reef, scuba, coll. R.W.M. van Soest, field nr. NIOP-E stat. 792/21, 6 January 1993; ZMA Por. 11564, Seychelles, Amirantes, N of Platte Island Atoll, 5.8167°S 55.3667°E, depth 6 m, reef, coll. R.W.M. van Soest, field nr. NIOP-E stat. stat. 796/42, 7 January 1993.

Description. Small white or beige-white globules (Figs 58a–d), with a single apical oscule, flush with the surface, which is optically smooth but feels rough. Size of body up to 1.5 cm high, 1 cm in diameter; oscule 2–3 mm in diameter. In preservation they stay white. Consistency firm.

Aquiferous system. Leuconoid.

Skeleton. (Figs 58e–g) Cortical skeleton (Fig. 58f) of intermediate sized triactines overlying a mass (Fig. 58e) of giant and smaller triactines forming the choanosomal skeleton supporting the leuconoid aquiferous canal system. The atrial skeleton (Fig. 58g) consists of sagittal triactines and tetractines, the latter with apical actines protruding into the atrial lumen. The oscular rim is supported by trichoxeas.

Spicules. (Figs 59a–e) Giant triactines, oxhorn-shaped triactines, small triactines, tetractines, trichoxeas.

Giant triactines (Figs 59a) of the main body wall, actines straight, tapering gradually to sharp points, equiangular and equiradiate or more often sagittal or with all actines of different lengths, 312– 628 –985 x 19 – 55.7 –93 µm.

Oxhorn triactines (Figs 59b) of the cortical skeleton, sagittal with curved paired actines and straight unpaired actines, unpaired actines 178– 245 –326 x 15 – 22.7 –31 µm, paired actines 216– 281 –372 x 16 – 21.6 –28 µm.

Small triactines (Figs 59c) of the main body and the subatrial region, sometimes equiradiate equiangular but more often irregularly sagittal, or T-shaped, unpaired actines 94– 172 –254 x 9 – 17.8 –26 µm, paired actines 100– 186 –303 x 11 – 16.6 –29 µm.

Tetractines (Figs 59d) of the atrial skeleton, sagittal, usually with unpaired actine shorter than paired actines, which are usually straight, occasionally slightly curved, unpaired actines 101– 186 –271 x 14 – 19.4 –32 µm, paired actines 136– 239 –380 x 9 – 17.1 –32 µm, apical actines slightly curved, 45– 84 –130 x 4 – 8.4 –11 µm.

Trichoxeas (Fig. 59e) of the oscular region, not common, almost invariably broken, 100–300 x 1–2 µm.

Distribution and ecology. Seychelles only, but widespread throughout the archipelagoes, on reefs, depths 1– 13 m.

Etymology. Pilula (L.) = small ball, a noun referring to the habitus.

Remarks. The size of all specimens is uniformly 1–1.5 cm high and 1 cm in diameter, and thus it is likely that this feature is characteristic for the species. The shapes of the triactines and tetractines are somewhat variable among the 5 specimens obtained of this species, but invariably there are giant triactines, smaller cortical triactines and smaller subatrial triactines. The atrial tetractines vary in the length of the paired actines, within and among specimens. However, the overall spicule package is similar in all and the lack of giant diactines is shared by all.

Similar-sized specimens were described by Jenkin (1908) from Zanzibar under the name Leucandra ananas (Haeckel, 1872), a species from the Northern Atlantic. This differs cleary by having tufts of large diactines of up to 3000 µm in length projecting from the surface. It is likely an undescribed species.

By the lack of diactines this species stands out among all known Leucandra species of the Western Indian Ocean region (but see below). There are no matching descriptions in the region.

We obtained a 28S sequence of the holotype of our new species and compared these to the sequences from GenBank of Leucandra nicolae Wörheide & Hooper, 2003 and a new species, L. mozambiquensis sp.nov. described below. There are no other partial 28SrRNA sequences of Leucandra available from the region and moreover the genus has been shown to be non-monophyletic (Dohrmann et al. 2006). In our Calcaronea phylogeny (Fig. 3) the three species grouped in a shared clade with modest bootstrap value (52%), with L. pilula sp.nov. and L. nicolae closer (bootstrap value 65 %). A separate inspection of the trimmed alignment of these three species (length 431 sites) showed 15 non-conserved sites, indicating the species are probably not closely related.