van Soest & Beglinger, 2009
Cliona caledoniae van Soest & Beglinger (2009) was recently discovered in the cold water coral reefs of Mingulay (Scotland). It excavates dead corals and is visible on the outside only by yellow papillae, which resemble other excavating sponges. However, the microscleres are characteristic thick, blunt-rayed spirasters unlike any others in the area (microscopic examination necessary).
Colour: yellow, or orange-yellow
Shape, size, and papillae: Excavating sponge, with exclusively alpha-habit (distinctly separate non-confluent papillae protruding from the corals). Papillae yellow, or orange-yellow, rather conspicuous, flush with the surface, often slightly elevated beyond the coral surface, but in preserved material the papillae tend to be contracted below the substratum level. The papillae turn brown in alcohol. Both optically 'closed' papillae, presumably exhalant, and optically perforated papillae, presumably oscular, occur. Papilla size variable, 1-4 mm diameter. Papillae unevenly distributed over the coral surface. Excavations are extensive chambers, up to 5 mm or more in diameter, filled with soft tissue of a pale brown or off-white colour. The branching corals and coral polyps are hollowed out to leave only a thin limestone wall.
Spicules: Tylostyle megascleres and spiraster microscleres. Tylostyles, robust, with usually slightly subterminal tyle, 246-360.9-426 x 8-9.8-12 mm; tyles 11-12.3-15 mm diameter. Spirasters, thick, blunt-rayed, with short axis, occasionally almost straight and with the rays concentrated at the extremities. Length: 19-24.3-31 5-6.8-9 mm, excluding rays which are 3-5.1-7 mm; number of rays 10-11.8-17.
Skeleton: The papillae are provided with the usual dense palisade of tylostyles, points outward, with intermingled microscleres in a moderate density. The intra-coral tissue contains scattered loose tylostyles, and microscleres are absent.
Ecology: Excavating dead Lophelia and Madrepora corals at 82-131 m depth.
Etymology: Named after Caledonia, the Roman name for Scotland.
Type specimens: Holotype: ZMA Por. 20174, Mingulay, Station BX48/06, 56.80548N 7.44198W, 127 m, in Lophelia pertusa, 14/7/06.
The new species is distinguished from the known north-east Atlantic Clionaidae species by its combination of commonplace tylostyles and a single category of thick-rayed amphiaster-like spirasters. Cliona lobata is the only species in the area with similar overall spiculation of tylostyles and spirasters, but it has two categories of spirasters the larger of which are longer and thinner (up to 65 mm), with up to 9 spiral curves (Topsent, 1900) and its papillae are usually not larger than 0.5 mm in diameter. Cliona celata has similar papilla size as the new species but these are usually much closer together, and the species lacks microscleres entirely. Excavations in the alpha-form of this species usually are thin, branching corridors and small galleries, not large chambers entirely filled with tissues as described above. Pione vastifica, very common in the Mingulay reefs, possesses next to tylostyles and thin microrhabds also rugose microxeas, usually in two sizeclasses. Macroscopically, Pione vastifica and Cliona caledoniae are similar and microscopic examination is necessary to identify either with certainty.
Source: Van Soest & Beglinger, 2009.