Clathrina sororcula, Van Soest & De Voogd, 2015

Clathrina sororcula View in CoL sp. nov.

Figures 7a–c View FIGURE 7 , 8a–e View FIGURE 8

Leucosolenia coriacea ; Burton, 1930: 2, in part (not: Montagu, 1814)

? Clathrina sp. Colin & Arneson, 1996: 59, photo 227; Lim, De Voogd & Tan,2008: 162.

Material examined. Holotype RMNH Por. 2576, Singapore, Pulau Subar Darat (Little Sister), NW side, 2.2149°N 103.8318°E, depth 10 m, SCUBA, coll. N.J. de Voogd, #SIN16/010406/138, 1 April 2006, GoogleMaps

Paratypes ZMA Por. 00135, Indonesia, Sulawesi, Salayar anchorage, 6.0963°S 120.4481°E, depth 0–36 m, trawl, coll. Siboga Expedition stat. 213, 26 September 1899 GoogleMaps ; ZMA Por. 00183a, Indonesia, Kalimantan, Karang Lintang, Pulau Palabangan , Moearas Reef , 1.7714°N 118.9615°E, depth 0–54 m, trawl, hard coral sand, coll. Siboga Expedition stat. 091, 22 June 1899 GoogleMaps ; RMNH 2065 About RMNH , Indonesia, Java Sea, Kepulauan Seribu ( Thousand Islands ), 5.7606°S 106.7546°E, depth 12 m GoogleMaps , SCUBA, coll. N.J. de Voogd, #SER.27, Kepulauan Seribu Expedition 2005, 17 September 2005 .

Description. Rather loosely anastomosed cushion of white, semi-transparent tubes ( Figs 7a View FIGURE 7 , 8e View FIGURE 8 ), encrusting rocks and mussels. Size up to 4 x 3 cm in lateral expansion, at least 1-3 cm in height in preserved condition. Several oscules are visible in the in situ photo, but they are solitary and flush with the surface and do not appear to be distinct endings of water-collecting tubes. Pale greyish brown to dirty white in preserved condition ( Figs 7b View FIGURE 7 , 8a View FIGURE 8 ). The preserved holotype is broken into two equally sized fragments ( Fig. 7b View FIGURE 7 ).

Skeleton. ( Figs 8b–c View FIGURE 8 ) Walls made up of three or more layers of robust triactines.

Spicules. Triactines only.

Triactines ( Figs 7c View FIGURE 7 , 8d View FIGURE 8 ), equiangular equiactinal, cylindro-conical actines with rather abruptly sharp-pointed ends, a small proportion are parasagittal, actines in a large size range, possibly divisible in two sizes, overall size 97– 151.6 – 201 x 9– 12.6 –21 µm.

Ecology. Shallow-water.

Distribution. Singapore, Indonesia.

Etymology. The word sororcula (L.) means ‘little sister’, referring to the locality Pulau Subar Darat, Little Sister Island.

Remarks. The new species differs from the Clathrina species reported here from Indonesian waters by the combination of white semitransparent color and robust spicules. Using the key of Klautau & Valentine (2003) this species keys out as the Northeast Australian Clathrina parva Wörheide & Hooper, 1999 . The skeleton and the spicules are indeed similar to the description of the type of that species, but the habitus and the size of the cormus are quite different: cormus may reach 4 cm in lateral dimension (1 cm in C. parva ), oscules are singly and flush (on the top of fused tubes in C. parva ), spicules are conico-cylindrical and sharply pointed (cylindrical and bluntly pointed in C. parva ). Furthermore, we assume that photo’s in Colin & Arneson (1996: Clathrin a sp. 227, Papua New Guinea) and Lim et al. (2008, Singapore) are also referable to the present species.

Burton (1930) referred this (and other specimens of the Siboga Expedition) to the European species Clathrina (as Leucosolenia ) coriacea ( Montagu, 1814) , which is erroneous because that species has much more densely anastomosed tubes and smaller spicules. Siboga specimens ZMA Por. 00136 and 00183b, identified by Burton also as Clathrina (as Leucosolenia ) coriacea possess tetractines, and are here assigned to Ernstia naturalis sp.nov. (see below).