Ulosa digitata (Schmidt, 1866)


Family : Esperiopsidae

Form: Massive-lobose, frequently extremely irregular and untidy in outline; crust or irregular cushions. Size varies from one or two to 10 or morecm in diameter.

Colour: Frequently yellowish, else a distinctive pinky orange or salmon pink (Methuen codes 7Ab and 7A7); seldom red.

Smell: None. Slime : Surface is slimy.

Consistency: Very soft, limp, easily compressible, somewhat elastic.

Surface: Uneven, often with irregular folds. Conulate, with the ends of fibres sometimes protruding from the conules, giving a somewhat hispid appearance. Foreign bodies are often incorporated into the surface (and may also be found throughout the skeleton fibres). Moderate friction.

Apertures: Oscules are irregularly dispersed and few in number. They tend to blend in with the generally ragged appearance of this sponge and so are not always obvious. Their rims are more or less raised, with ragged edges. Sizes range up to 1cm diameter, but are usually smaller. They remain open on collection and preservation.

Contraction: Not noticeable.

Internal characters

Skeleton: An isotropic reticulation of spongin fibres cored with styles. The primary fibres extend to the periphery, the secondaries interlink the primaries. The primaries are ca. 30-100Ám in width, and are always polyspiculate with spicules compacted together along the fibre axis. The secondary fibres are ca. 20-30Ám wide and are poorly spiculated, hence consisting mostly of spongin. Further slender spicules may be sparsely scattered outside the fibres. Foreign bodies may be found within the primary fibres. The ectosomal skeleton consists of fine spongin fibres which may lack spicules.

Spicules: The spicules are styles which can be classified into "robust" and "slender" categories. The former are ca. 170-(220)-260 x 7-10Ám. The "slender" styles are ca. 110-235 x 2-3Ám, and may occasionally be styloid or oxeate.

Habitat: In wave-sheltered locations in the infralittoral, frequently growing on or around algae or sessile/encrusting animals.

Distribution: A southern species: Plymouth, Channel Islands, Skomer, Isle of Man, Roscoff, Azores.

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

Identity: This species is similar in overall appearance to Dysidea fragilis (q.v.), but it may be distinguished in the field by colour, a more 'ragged' appearance, its softness, and the absence of oscular ridges. In a section the spongin skeleton cored by styles is distinctive. Acervochalina limbata (q.v.) similarly grows on seaweeds, but is smaller, has a more regular outline and is confined to the shore; its skeleton consists of fibres cored with oxea. With experience, Ulosa digitata is quite easy to identify in the field.

Voucher: BELUM : Mc1774. Skomer Is., Wales

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

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