(Bowerbank, 1858)
Species Overview
Iophon nigricans (Bowerbank, 1858) forms soft yellow fingers issuing from a broader base. When taken out of the water it turns black or dark after some time. It differs from the sympatric I . hyndmani in lacking a second category of smaller acanthostyles.
Taxonomic Description
Colour: Off-white or grey, through bright yellow to bright orange, blackening on contact with air and on preservation.
Shape, size, surface and consistency: (Iophon nigricans MCS2) (Iophon nigricans MCS3) Ascending finger-like growths with broader bases, cushions, massive-lobose. Oscules are slightly raised, with transparent rims, and are found along the edges of the fingers and on raised ridges of lobed form. Surface irregular, with raised areas of denser appearance supported by the underlying skeleton, with a transparent surface membrane between these. Contraction: oscules disappear and surface membrane collapses on removal from water. No smell. Consistency fairly soft and crumbly.
Spicules: (Iophon nigricans V spics) Megascleres : Ectosomal tylotes with swollen microspined ends, stout: 225-250 µm x 6-7 µm; acanthostyles stout: 210-260 µm x 10-11 µm.
Microscleres : Anisochelae in two size categories: ca. 26-30 µm and 10 µm; bipocilles small: ca. 7.5 µm.
Skeleton: A fairly regular isodictyal reticulation of acanthostyles which is reminiscent of Myxilla spp. There are dense bundles of tornotes lying tangentially and at an angle to the surface. Bipocilles and spurred anisochelae are scattered throughout the body with small anisochelae more abundant at the surface.
Ecology: Found in sheltered or moderately exposed sites, with moderate to strong tidal streams. On rocks, boulders, steep rockfaces and shells. Circalittoral. Common on brachiopod valves in Firth of Lorne, Scotland. Down to 108 m.
Distribution: Common and widespread in the English Channel, Ireland and W Scotland; Sweden, Norway; south to NW coast of Spain.
Etymology: The name refers to the darkening of this species after collection.
Type specimen information: The type is in the Natural History Museum, London (Halichondria nigricans). MCS voucher: BELUM Mc1182, Maidens, N-Ireland.
Remarks
The bipocilles, spurred anisochelae and microspined tylotes are characteristic for the genus Iophon . The species is distinguished from the other common sympatric Iophon species by the absence of a smaller category of (echinating) acanthostyles. The blackening on death is very noticeable. Larger specimens may resemble Myxilla incrustans or Myxilla rosacea superficially.
From Northern European waters (Norway, Iceland) several related species of Iophon have been recorded: I . piceus Vosmaer, 1882b which has larger acanthostyles, and I . variopocillatum Alander, 1942 which has two size categories of bipocilles. Their status remains uncertain.
Sources: B.E. Picton, S.M. Stone, D. Moss (Ackers et al., 1985, 1992).