Form: Massive-lobose, often having the form of a flattened hemisphere, composed of a network of anastomosing plates and ridges, with the orange crests showing through but the interstices usually being filled with silt. The whole sponge may approximate the form, appearance and size of a human brain. At lateral growth areas repent and compact coalescing branches can occur. In places, tangled masses of these branches can themselves form the body of the sponge. Attachment to the substrate may be discontinuous. Size up to 10cm thick by 30cm in diameter, but smaller "fist-sized" specimens are more typical.
Colour: Bright to buff orange; yellow (butter colour). "Yellow-orange in the basal regions, becoming more brown in top". Eventually turns grey in alcohol.
Smell: Very slight, sweetish.
Consistency: Compact, firm.
Surface: An irregular mass of laterally coalescing papillae-like branches, which may be the only part of the sponge visible through silt in situ. Smooth, moderate friction.
Apertures: Oscules are borne at the ends of the papillae and are clearly visible under water. The papillae collapse on collection and the oscules are then no longer apparent.
Skeleton: Subradiate, the radial arrangement being apparent near the surface, where the spicules are loosely arranged into ascending bundles. The points of the spicules penetrate the sponge surface to form a sub-palisade layer, ca. 180Ám deep.
Spicules: Megascleres are large tylostyles in the range 160-950 x 4-16Ám. They are not differentiated into two size ranges, but a large number fall within the 550-850Ám range. A high proportion of the spicules are straight, with only a few being slightly curved. Vermiform spicules have also been reported. The heads are often mucronate to a greater or lesser extent, but a few are smoothly rounded. There are no microscleres.
Habitat: Found in the silty brackish water of harbours, estuaries and lagoons where there are moderate tidal currents. It colonizes shells (often over-growing them so that the sponge is free-standing), boulders and sea walls or similar structures. Usually sublittoral but in places, especially if shaded, can occur on the lowest shore.
Distribution: Known in the British Isles only on the Channel coast -in the Fleet (Dorset), Poole Harbour (Dorset), and Southampton Water (Hampshire). Also known from the River Morlaix in Brittany, and from the Mediterranean.
Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.
Identity: The large size of the tylostyles and estuarine habitat are characteristic. The form could be likened to a large, very ragged Polymastia boletiformis. The stubby branching processes are reminiscent of those of Homaxinella subdola.
Voucher: BELUM : Mc657. Off Roscoff, English Channel. Coll. L. Cabioch, S. M. Stone.
Editors: D. Moss, B.E. Picton.
|Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland |
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