Bowerbank, 1872
Species Overview
Tethya norvegica Bowerbank, 1872 is a small globular yellow sponge with warty surface. It replaces the common European "orange sponge" (T. aurantium) in the Northern and Arctic Atlantic. Differences with T . aurantium are microscopical.
Taxonomic Description
Colour: In life is ochraceous yellow (specimen from Ramsfjord).
Shape, size, surface and consistency: Normally spherical, diameter 1-2 cm. Surface with contiguous, conulose papillae. Consistency resilient but somewhat fragile, not hard. Some specimens carry a few large, pedunculate buds 1-2 mm in diameter. Cortex thin, 1 mm in depth in a sponge of 1 cm diameter.
Spicules: (Tethya norvegica spics) Megascleres : Principal styles (strongyloxeas) 1200-1500 x 20 µm with the proximal end often slightly enlarged (subtylostyles). Slender styles 500-700 x 5-10 µm.
Microscleres : (Tethya norvegica asters) Megasters-spherasters 20-60 µm (mainly 30-50 µm) with ratio of ray/centre (R/C)= 0.8-1 and a variable number of rays (generally about 15) frequently with spines, divided ends or other irregularities Micrasters: oxyasters and rare strongylasters 6-15 µm (mainly 8-12 µm) with 8-12 almost smooth rays and an ocasionally slightly developed centre.
Skeleton: (T. norvegica cortex) The radiate bundles of styles (strongyloxeas) are dense, each one terminating in a cortical papilla surrounded distally by a small fan of slender styles. The bundles are often spirally arranged. The megasters are located in the cortex, mainly in the outer layer with a sparse and irregular distribution. The micrasters form a dense sheet under the surface of the sponge and are also abundant both in the cortex and in the medulla. No morphological differentiation has been observed between the cortical and medullar micrasters but there is a slight difference in size with the smaller micrasters being found more frequently in the cortex than in the medulla.
Reproduction: Many specimens in the BMNH collection display external buds. When present, these buds are characterized by their large size occurring in restricted numbers on eachh specimen. A sampling data are lacking, it is not possible to give information about the seasonality in the bud production or sexual maturity. Specimens collected in July did not show budding or sexual maturity.
Ecology: Samples of the Ramsfjord population were collected under stones at a depth of about 10 m. The species shows a bathymetric distribution ranging from 10 to about 800 m. In situ, the sponges are sometimes double the size of a collected specimen.
Distribution: Norway, White Sea, Bear Island, Spitzbergen, Novaja Zemlja, Iceland, The Faroes, Scotland, ?Sweden.
Type specimen information: The type is in the Natural History Museum, London.
Remarks
Sarà et al., 1992 re-instated this species as valid after careful comparison, including electrophoretic studies, with the two other Tethya species of Europe, viz. T . aurantium and T . citrina .
According to Topsent (1918: 580-582 fig. XXV) there is a considerable variability in the shape of micrasters of T . norvegica . He referred to Merejkowsky' s observations on the White Sea specinens of T . lyncurium , having surface micrasters of globular shape with the diameter of the centre being larger than the length of the short, conical rays and short and conical rays
on the surface.
The species differs from T . aurantium in size (only up to 2 cm in diameter), the megasters are generally much smaller and their RC ratio is high, i.e. they have less pronounced centres.
Source: Sarà et al., 1992.