Leuconia johnstoni (Carter, 1871)


Family : Baeridae

Form: Normally consists of groups of flask-shaped lobes, with terminal oscules, resembling a cluster of Scypha sp., but with a common basal crust.

Colour: White, beige.

Smell: None. Slime : None.

Consistency: Firm.

Surface: Even, non-hispid.

Apertures: Oscules at tips of lobes, with fringe of short, even spicules.

Contraction: None.

Internal characters

Skeleton: The ectosome has a tangential layer of triradiates and the facial rays of large quadriradiates, with groups of microxea and quadriradiates. The endosomal skeleton consists of small quadriradiates. The skeleton of the chamber layer consists of scattered triradiates and small quadriradiates.

Spicules: Spicules are calcareous. Ectosomal triradiates (a) have rays 200-300 x 15-20Ám. Triradiates of chamber layer (b) have rays 100-1000 x 10-70Ám. Large ectosomal quadriradiates (c) are ca. 650 x 80Ám (ectosome); sagittal quadriradiates of two types, (d) 30-40Ám (paired rays), 60Ám (basal and apical) x 8Ám (chamber layer); and (e) 250 x 6Ám (associated with microxea in ectosome). Endosomal quadriradiates (f) with rays 200-300Ám. Microxea (g) are ca. 60-80 x 5Ám.

Habitat: Vertical surfaces of rocks 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.

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

Identity: Can be confused with Leuconia gossei (Burton, 1963, p.505) and Leucosolenia nivea (q.v.). The presence of sagittal quadriradiates in the endosomal layer, with large quadriradiates in the ectosome, is diagnostic.

Voucher: BELUM : Mc1843. Strangford Lough, Down.

Editors: D. Moss, B.E. Picton.

 Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland