(Montagu, 1818)
Species Overview
Hymeniacidon perlevis (Montagu, 1818) is one of the most common species along the coasts of Western Europe. It is orange and has an irregular surface, often with lower or higher irregular projections, and this distinguishes it from the common Halichondria panicea (which is yellow-green, has regular chimneys and a smooth surface). Oscules are inconspicuous. It is compressible and feels smooth. It occurs from the mid-littoral ddown into the shallow sublittoral, and it prefers slightly silted environments.
Taxonomic Description
Colour: Yellow to orange to blood-red. Shore forms tend towards blood-red, whilst sublittoral forms tend to be pinkish-red. Note the colour changes on preservation—the sponge goes patchily dark brown-black in alcohol. The degree of blackening depends (?) on the depth at which the individual grows, varying from no blackening for shore forms to an increasing blackening with depth.
Shape, size, surface and conistency: Thin sheets, cushions (Hymeniacidon perlevis MCS2), to massive-flanged, rarely branching-erect. More than one form can be detected in the intertidal and shallow sub-littoral. It is possible tbat these may eventually be recognized as including more than one distinct species.
(a) Thin sheets, fully exposed on lower shore up to mid-tide level. Gains some shelter by growing along crevices and fault-lines and Iying at the base of right-angled rock. Protective cover (e.g. algal canopy) is usually non-existent, with adjacent surfaces clean and dry. The only protection the animal seems to have is derived from (?) symbiotic algae living in the surface layers, causing a discolouration of the surface to a dull greenish-orange (deeper layers of body are a typical bright orange). Surface is even, smooth to minutely tuberculate.
(b) Cushions half-exposed at LW and in the sublittoral fringe, favouring angles in rock and Laminaria holdfasts. Conditions generally muddy with a layer of fine muddy silt smothering the animal. When brushed aside, the colour is seen to be a clear pinky-orange. Surface even but distinctly tuberculate.
(c) Massive-flanged forms sometimes seen on the lower shore and in sublittoral fringe where conditions are distinctly muddy (e.g. estuaries and harbours) with fast-flowing currents. The animal can be overlooked as it is buried in the mud with only the tips of the flanges or oscular chimneys showing. Underneath, the colour is seen to be a deep dirty orange to brick-red. Surface uneven, wrinkled, irregularly folded, with well-developed tubercles.
(d) In the sublittoral, cushions are generally found which can form large, spreading pinky-orange patches on hard substrates (e.g. rock) in semi-fast current areas.
Lateral expansion of all forms may be considerable, 20 cm or more; thickness may vary from a few mm to 10 cm or more. Flanges and irregular projections may be up to 3 or more cm.
Surface variable, smooth, tuberculate, thrown into irregular folds, or else covered with branching processes (Hymeniacidon perlevis Holland). Oscules scattered, level with surface or at top of branching processes. Not conspicuous. Smell sweetish, vaguely distasteful. Consistency firm, compact, compressible.
Spicules: (Hymeniacidon perlevis spics) Megascleres are styles only of simple, smooth form, 175-475 x 3-12 µm; sometimes they are differentiated into 2 size categories in which case the smaller spicules are found mainly in surface layers. Occasionally there are tylote-like swellings at or near the rounded ends. There are no microscleres.
Skeleton: Halichondrid. Ectosomal skeleton is a tangential layer of spicules inter-crossing in all directions, or of brushes of spicules set vertically to surface. Choanosomal skeleton disordered, a confused reticulation with a tendency to fom ill-defined ascending fibres. Spongin is scarce.
Ecology: On stones, rocks, shells, Laminaria holdfasts; may be buried deep into the sediment with long projection sticking out to the surface. Many invertebrates are associated with this species: nematodes, annelids, crustaceans (Frith, 1976). Tube-living Amphipods may form characteristic warty type burrows in the surface.
Distribution: British Isles, Netherlands, Belgium, France, Spain, the Mediterranean, Canary Islands, Azores. Reported from many areas elsewhere in the world, but these records need verification.
Etymology: Perlevis (Latin)= very smooth, referring to the surface.
Type specimen information: 2 slides in BMNH, unregistered (Bk.513) "Hymeniacidon perlevis Montagu (Halichondria Montagu) from Type. Devon". MCS voucher BELUM Mc108. Portrush, Co Antrim, Ireland, littoral form. BELUM Mc612, Saltee Isl., Wexford, S Ireland, sublittoral form.
Remarks
From the only other Hymeniacidon species from Western Europe (H . kitchingi ), this species differs in the more massively encrusting habit and orange colour (versus a more thinly encrusting habit and beige-yellowish), and in most individuals also in the possession of longer and more robust styles. The great variability of the style sizes (175 to 475 µm), as well as the varied reaction to preservation in individuals may be regarded as evidence for the existence of at least two species, but so far differentiation of these is uncertain.
Sources: Ackers et al., 1992.