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(Fristedt, 1885)

Species Overview

Hymedesmia (Stylopus) coriacea (Fristedt, 1885) is a light-brown thin crust on rocks and shells. The surface is superficially smooth and somewhat slimy, and characteristically punctate. Oscules are scattered and slightly elevated. It is a common species with a large range from the Arctic into the Mediterranean.

Taxonomic Description

Colour: ApparentIy variable, but normally light brown, grey-brown, or yellow to orange-brown tinges predominate (possibly the substrate colour influences the observed colours).
Shape, size, surface and consistency: Thin encrustations, 2-3 mm thick and up to 15 cm in lateral expansion, with a smooth surface, which is microscopically very lightly conulose. Excurent canals may be visible. Oscules scattered, may be slightly raised over the surface. Skin rather tough, somewhat slimy, only slightly transparent, showing subdermal holes underneath porefields (punctate). Consistency fragile, difficult to remove from the substrate.
Spicules: (Hymedesmia coriacea spics) Megascleres: Ectosomal smooth tornotes, sometimes faintly polytylote, sometimes strongylote, sometimes anisotornote (when one end is tylote the other mucronate), rather uniform in size in the studied material: 156-240 x 2-3 µm; acanthostyles, entirely spined, with a thickly spined head, quite variable in size with a tendency to occur in two overlapping size categories, 40-312 x 3.5-8 µm. Microscleres absent.
Skeleton: Ectosomal skeleton: the organic membrane is strengthened by tangential tornotes and carried by skeletal columns or brushes of subtylotes. Choanosomal skeleton: basally there is a spongin membrane in which single acanthostyles are embedded with points erect. These are only detected if material is wholly removed from the substrate. Next to these, there are bundles of tornotes, 2-20 spicules per cross-section, at intervals of 150-250 µm, which rise up from the level of the points of the acanthostyles towards the ectosome. There they fan out to form the ectosomal skeleton.
Ecology: Common in the kelp zone, on rock surfaces, valves of scallops and other shells; also known from deep water coral beds, down to 1287 m (Lundbeck, 1910).
Distribution: Apparently occurring from the low Arctic into North African waters, including the Mediterranean.
Etymology: coriaceus (Latin) = leathery, referring to the consistency in dry condition.
Type specimen information: No data; MCS voucher BELUM Mc164, Strangford Lough, N Ireland.

Remarks

The appearance seems to be fairly characteristic, but caution is needed because other less well-known Hymedesmia species without microscleres have been described.
The reasons for preferring the name coriacea over widely-used synonyms dujardini or broendstedi were given by Alander(1942): Bowerbank (1866) mistook Haliscarca dujardini Johnston, 1842 for the present species and used it for the combination Hymeniacidon dujardini. Burton (1930) concluded that a new name was needed and proposed broendstedi. He overlooked, however, that Stylopus coriaceus Fristedt (1885) (Stylopus coriaceus), described from Swedish waters, is a clear synonym.
For the time being we assume that Hymedesmia hibernica Stephens (1921) is also a synonym of this species as her description falls within the variation of H. coriacea as presently understood. A revision of Stephens material is needed and may show that the tow are distinct species.
Two features of this common sponge are apparently subject to considerable variation, viz. life colour and acanthostyle sizes. Colour, according to the respective authors, may include brown-red to green(Fristedt), ochre-yellow to deep amber (Bowerbank), yellow or grey (Topsent), light brown (Pulitzer-Finali, Van Soest), and rosy (Cruz). Acanthostyles in two size categories: 108-120 and 280-312 (Norway: Van Soest), 70-96 and 150-170 (Brittany: Van Soest), 85-110 and 160-225 (Naples, Topsent), 56-96 and 120-152 (Tenerife, Cruz). Acanthostyles in a single size category: 84-130 (Brittany: Van Soest), 48-168 (Ireland: Van Soest, Picton in Ackers et al.), 40-80 (Azores: Van Soest), 96-144 (Tenerife: Van Soest), 120-180 (Sweden: Fristedt) 83-220 (Greenland, Iceland: Lundbeck). It is concluded here, that these observations are best explained as a random individual variation.
Topsent (1936), in dealing with Mediterranean sponges, distinguished both dujardini (as Hymedesmia) and coriacea (as Anchinoe) arguing that both differ in the roughness of the skin; also coriacea would pass from a Hymedesmia—stage to an Anchinoe-stage (=Phorbas) during growth. Boury-Esnault (1969, 1971) kept the same view though she used the name broendstedi instead of dujardini. Recently, Topsent's and Boury-Esnault's Anchinoe coriacea was redescribed as a separate Mediterranean species, Phorbas tailliezi Vacelet & Perez (2008).
Hymedesmia pulposa Topsent (1925), is a red species from the Mediterranean, which is possibly closely related to H. coriacea.
The present species is the type of the genus Stylopus Fristedt (1885), which is employed for species of Hymedesmia-architecture and-spiculation, but lacking the chelae. There is no clear indication for the assumption that Hymedesmia species lacking chelae are a monophyletic group. Indeed, when the variability of ectosomal megascleres of e.g. Alander's (1942) Stylopus species is taken into account, it is even quite unlikely. For that reason, the use of Stylopus (and its sister genus Ectyostylopus Topsent (1928) which was erected for Stylopus species with two size categories of acanthostyles) is abandoned.
The large distribution of Hymedesmia (S.) coriacea from the Arctic to the Canary Islands and into the (Western) Mediterranean, is rather unusual in sponges. The range possibly even exceeds that of Halichondria (H.) panicea in its southern limits. In contrast with this species, H. (S.) coriacea is not known from the east coast of North America.
Sources: Van Soest, 1987; Ackers et al., 1992 (B.E.Picton, S.M. Stone, D. Moss).

Hymedesmia coriacea