(Grant, 1826)
Species Overview
Leuconia nivea (Grant, 1826) forms white or greyish irregularly encrusting masses, thin sheeted or elevated into folded sheets. Surface feels rough but is otherwise smooth. It is a very common intertidal and shallow subtidal calcareous sponge, especially in exposed rocky areas, surge gullies and under boulders. It occurs from the Artic to the Mediterranean.
Taxonomic Description
Colour: White, pale grey.
Shape, size, surface and consistency: (Leuconia nivea MCS2) Encrusting sheets to cushions with lobes and ridges. Surface smooth. Apertures small, distributed along the tops of lobes or ridges, "naked'' (i.e. without collar of spicules). Consistency firm, crisp, friable.
Spicules: (Leuconia nivea spics) Calcareous. Ectosomal triactines with rays: ca.120 µm; those of the chamber layer: 50-1200 µm.
Choanosomal tetractines sagittal with paired rays: ca. 20 µm and basal ray: ca. 60 µm.
Microxeas: 40-60 µm.
Skeleton: The ectosomal skeleton consists of several tangential layers of triactines; the skeleton of chamber layer is of triactines and microxeas, irregularly arranged. The choanosomal skeleton, and linings of exhalant canals, are tangential layers of tetractines.
Reproduction: Oocytes in July and August (Dubosq and Tuzet, 1942).
Ecology: In strong water movement beneath boulders in shallow water and in surge gullies on vertical rock surfaces. Littoral to 128 m.
Distribution: From Spitsbergen and Norway in the north, via Heligoland, British Isles and France to the Mediterranean in the south. A common species in the British Isles.
Etymology: Niveus (Latin) = snowy, referring to the colour.
Type specimen information: No type material in BMNH. MCS voucher BELUM: Mc1778, St. Kilda, W. Scotland.
Remarks
Superficially this species can be confused with Leuconia johnstoni and Leuconia gossei . The first has a persistent vase-or tube shaped habit, the latter is a more massively rounded species. Spicules of L . johnstoni are similar but this species has very large tetractines (rays up to 300 µm). The spicule complement of L . gossei includes large oxeas (400-600 µm long) not found in the others. It would be useful to see if the three species occupy different ecological
niches.
Source: Ackers et al., 1992 (S.M. Stone, B.E. Picton, D. Moss)