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Description of a New Deep-Water Calcareous Sponge (Porifera: Calcarea) from Northern California1
ABSTRACT: A new species, Sycon escanabensis Duplessis & Reiswig, is described from material retrieved by submersible from 3500 m depth in the Escanaba Trough, central Gorda Ridge, off northern California. The species differs from all other members of the genus by the combination of conspicuous tripartite body organization and slender, lancet-head diactins that ornament the external surface and the oscular margin. This is the first deep-water (> 1000 m) calcareous sponge described from the North Pacific Basin.
MEMBERS OF THE PORIFERAN class Calcarea have often been considered to be restricted to the upper 200 rn of the ocean by physical factors (Bergquist 1978), namely the calcium carbonate compensation depth, below which exposed calcareous skeletons pass fairly rapidly into solution (Gage and Tyler 1991). Indeed, the skeletal remains of calcareous sponges are rarely encountered in sediments at depths beyond 2500 m, suggesting their absence as members of deep-water faunal communities. In recent years, however, an increasing number of living calcareous specimens have been discovered at depths below 1000 m. These reports have been primarily from the Norwegian, Greenland, and Arctic Seas (Arnesen [1920]: 1 location; Borojevic and Graat-Kleeton [1965]: 7 locations; Reid [1968]: 3 locations; Tendal [1989]: 40 locations). The deepest specimen reported from the Atlantic region is Sycon abyssale from 4000 rn (Borojevic and Graat-Kleeton 1965). This series of unexpected occurrences was thought to be attributable to the unusual combination of low temperatures and high overturn (dynamic instability) in this region, modifying the solution dynamics of calcium carbonate. However, Vacelet (1989) has found calcareous sponges at eight deep locations in the Mediterranean Sea, the deepest at 2775 m, casting serious doubt upon the unique environment hypothesis.
These calcareous sponges have all been, with rare exception, members of the cosmopolitan genus Sycon. The only deep-water calcareous sponge reported from the North Pacific is an unidentified specimen discovered in the Kurile Trench at 5045 m (Koltun 1970). Here we describe a new deep-water Sycon species (four specimens) from the Northeast Pacific. This is only the second report of occurrence of deep-water Calcarea from this region and the first report with a full species determination.
MATERIALS AND METHODS
The two complete specimens, after being...