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Carter, 1871a

Species Overview

Leuconia johnstoni Carter (1871a) is a whitish mass of flask-shaped lobes with a common encrusting base. It has the firm, slightly rough and incompressible aspect of most calcareous sponges. It may be distinguished from Leucandra gossei and Leuconia nivea by its rough surface and by details of the spicules. It occurs on the west coasts of the British Isles, France and Spain.

Taxonomic Description

Colour: White, beige.
Shape, size, surface and consistency: Normally consists of groups of flask-shaped lobes, with terminal oscules, resembling a cluster of Sycon sp., but with a common basal crust. Surface even, roughish but non-hispid. Oscules at tips of lobes, with fringe of short, even spicules. Consistency firm.
Spicules: (Leuconia johnstoni spics) Calcareous. Ectosomal triactines with rays: 200-300 x 15-20 µm. Triactines of chamber layer with rays: 100-1000 x 10-70 µm.
Large ectosomal tetractines: ca. 650 x 80 µm; sagittal tetractines of two types: 1) 30-40 µm (paired rays), 60 µm (basal and apical) x 8 µm (chamber layer); and 2) 250 x 6 µm (associated with microxeas in ectosome). Choanosomal tetractines with rays: 200-300 µm.
Microxeas: ca. 60-80 x 5 µm.
Skeleton: The ectosome has a tangential layer of triactines and the facial rays of large tetractines, with groups of microxeas and tetractines. The choanosomal skeleton consists of small tetractines. The skeleton of the chamber layer consists of scattered triactines and small tetractines.
Reproduction: Oocytes in July-August (Dubosq and Tuzet, 1942).
Ecology: Vertical surfaces of rock and wrecks in sheltered conditions, even with moderate tidal streams.
Distribution: British Isles (? extending to N. of Scotland, E coast of UK?). Channel coasts of France; Spain.
Etymology: Named after Dr George Johnston, author of an early (1842) monograph on the "British Sponges and Lithophytes".
Type specimen information: BMNH 1847.9.7.74 (dry), Johnston Collection (as Leucandra), BMNH 1897.2.26.1 (dry + slide). MCS voucher BELUM: Mc1843. Strangford Lough, N Ireland.

Remarks

It can be confused with Leucandra gossei and Leuconia nivea. The presence of sagittal tetractines in the choanosomal layer, with large tetractines in the ectosome is diagnostic.
Source: Ackers et al., 1992.

Leuconia johnstoni