Homaxinella subdola (Bowerbank, 1866)


Family : Suberitidae

Form: Irregularly branching-erect. The branches sometimes coalesce but never produce the lamellate forms found in other Axinellid sponges. The side branches tend to arise at right angles to the main stem, which gives it an untidy, 'bushy', appearance. The branches are circular in cross-section, borne on a thinner, wiry stalk. Up to 15cm high.

Colour: Pale yellow, deep orange, orange, brownish-yellow or golden-yellow when alive; becomes creamy white in alcohol.

Smell: None or slight?

Consistency: The branches are firm, tough and elastic but collapse if compressed when alive. The stalk is wiry.

Surface: Even, slippery, smooth; in older specimens minutely hispid.

Apertures: The oscules are small, not numerous, and disposed irregularly on the branches. They become inconspicuous on collection.

Contraction: Considerable lateral contraction of the branches occurs on collection. This is in contrast to the other Axinellids, which do not contract markedly in this manner.

Internal characters

Skeleton: A plumose axial core of loose fibres of long styles, which are surrounded by a dense sub-surface layer of irregularly arranged spicules. Some of these lie at right angles to the surface (occasionally piercing it); others are tangential to it. The intervening space between the two main skeletal areas is occasionally bridged by thin, almost imperceptible, fibres of spicules. Small amounts of spongin are present.

Spicules: The megascleres are smooth, usually straight, styles, which vary in size from 270-(440)-560 x 5Ám. There are no microscleres.

Habitat: Found in sheltered and semi-exposed conditions. On horizontal and slightly inclined rock, covered with a layer of silt. Out in the open on sheltered bottom plains, or at the bottom of gullies, which create relatively sheltered conditions in otherwise exposed situations. Circalittoral (?): at Lundy at 10m or deeper. Raspailia hispida, Raspailia ramosa and Axinella dissimilis are other branching species often seen in the vicinity.

Distribution: "British Isles". Also reported from "Sea of Japan; Sea of Okhotsk " In the UK this is a southern species; recently recorded from the Scilly Isles; Lundy; Devon; and Skomer. The type locality is Guernsey.

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

Identity: Alive the appearance lies between that of Axinella dissimilis and Haliclona oculata. However the oscules of Homaxinella subdola are less distinctive and not arranged in rows. In the field the best identifying character is probably the wiry stalk, which can be felt if not seen among the underlying 'turf'. The untidy appearance of the sub-branching, caused by the secondary growth of short, stubby branchlets, may also prove to be a useful character, but this needs testing. The side branches come off more or less at right angles - a very characteristic feature. There is a slight possibility of confusion with Adreus fascicularis (q.v.) which is much more wiry and on average a smaller sponge which does not branch 'untidily' as does Homaxinella subdola. Adreus fascicularis also has distinctive lines/grooves running along the branches.

Voucher: BELUM : Mc481. Skomer Island.

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

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