Hymedesmia jecusculum (Bowerbank, 1866)


Family : Hymedesmiidae

Form: Thin sheets, up to 10cms across, but smaller typically.

Colour: Deep orange or red.

Smell: None.

Consistency: Soft.

Surface: Smooth, with subsurface exhalent canals visible. Densely covered with oval pore areas.

Apertures: Oscules may not be apparent. Pores in oval pore-sieve areas with smooth tissue between.

Contraction: Hard to determine because of thinness of sheets.

Internal characters

Skeleton: Hymedesmoid, with large primary acanthostyles and also smaller acanthostyles echinating the substrate. The rest of the skeleton consists of flexuous columns or fibres of many parallel tornotes, which fan out to run parallel with the surface. Arcuate isochelae reinforce the ectosome.

Spicules: Primary acanthostyles (a) measure 360Ám in length by ca. 7.5Ám in width. The head is thickly set with spines, whilst small, rather scattered, spines extend along the shaft but are much less frequent in the distal half. There is usually an abrupt curvature just above the head, the rest of the shaft being straight. The smaller acanthostyles (b) measure 120Ám in length by 5Ám in width. They are straight or very slightly curved, and conspicuously spined along the whole length. The spines on the head are fairly long, those on the shaft recurved. The tornotes (c) are slightly fusiform, thin, measuring 285Ám in length, by 3.5Ám in width. They are symmetrical, pointed at both ends. Microscleres are arcuate isochelae (d), ca. 20Ám in length.

Habitat: On bedrock and boulders, usually in deep water below 25m depth, but originally described from a cave in the intertidal zone. On horizontal rock in clear water.

Distribution: West coast of Ireland and Scotland, this is the commonest Hymedesmia species in diving range in these areas.

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

Identity: External appearance is not particularly helpful, but the pore sieves and thin sheet may suggest a hymedesmid sponge. The spicule complement and sizes are distinct from the other Hymedesmia species in this Guide, but there are many other Hymedesmia species and the complex is currently ill-understood.

Voucher: BELUM : Mc1309. Loch Duich, Scotland

Editors: Christine Morrow, Bernard Picton & Rob van Soest.

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