Grantia compressa (Fabricius, 1780)


Family : Grantiidae

Form: Flat, like a small hot water bottle, but may be tubular, or composed of contorted flat lobes; with a very short stalk.

Colour: White or occasionally brown.

Smell: None.

Consistency: Moderately firm, can be bent through 180 deg. without breaking.

Surface: Smooth, has a moderately high friction when stroked.

Apertures: There is usually a single, smooth-rimmed, terminal oscule. Occasionally there may be several oscules along the margins.

Contraction: Not noticeable.

Internal characters

Skeleton: The ectosomal skeleton is a tangential layer of triradiates with 'tufts' of oxea projecting beyond the surface. The skeleton of the chamber layer consists of regularly overlapping triradiates. There is an endosomal skeleton of paired rays of triradiates and a tangential layer of triradiates and quadriradiates lining the central atrium.

Spicules: These are calcareous. Ectosomal triradiates (a) have rays 100-120 x 8Ám, oxea (b) (resembling hockey sticks) are 100-300 x 8Ám. Overlapping triradiates (c) have paired rays 80-120 x 8Ám and basal rays 200-300Ám. The endosomal triradiates are 100-150 x 5-8Ám; quadriradiates 100-150 x 5-8Ám with apical rays 40-80 x 8-12Ám.

Habitat: The main habitat is the sea shore where specimens are found attached to the underside of overhangs, often in abundance; they also occur commonly in the shallow sublittoral, e.g. on kelp stipes (? often associated with red algae). In the east Atlantic "from littoral to 288m".

Distribution: A common species in the British Isles. Arctic to Channel Islands.

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

Identity: By eye alone, provided specimen is simple, flattened and has a smooth surface. Many other forms exist and these need to be checked microscopically. There is considerable overlap between G. compressa which may be tubular instead of flat, and Scypha ciliata which may have a smooth outer surface instead of a finely papillate one.

Voucher: BELUM : Mc104. Portrush, Co Antrim.

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

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