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(Topsent, 1888a)

Species Overview

Haliclona (Rhizoniera) viscosa (Topsent, 1888a) forms purple, pink or brownish spreading cushions with rows of large oscular chimneys. The surface is distinctly punctate and maybe rugose in large specimens. The consistency is firm. The species is slimy to the touch and when broken produces a lot of slime. It occurs in deeper sublittoral waters, on vertical rock faces in areas with considerable water movement.

Taxonomic Description

Colour: Greyish-purple, commonly verging to yellow towards the base. The colour turns to blackish-brown when the sponge is exposed to the air.
Shape, size, surface and consistency: (Haliclona viscosa 1) Thickly encrusting to massive with chimney-or volcano-shaped osculiferous elevations (Haliclona viscosa England). It may be similar to Hymeniacidon kitchingi. Commonly the oscules are large in number and situated in series at the top of isolated or fused elevations. The degree of fusing of these elevations is variable. The species may reach a considerable size: it may grow out to patches with a diameter of 30-40 cm and a height of 1.5-5 cm. The diameter of the oscules varies from 1-5 mm. Consistency rather firm, but very friable; extremely slimy. The surface is punctate, smooth, but somewhat irregular caused by ridges and grooves (Haliclona viscosa large).
Spicules: (Haliclona viscosa skdraw) Rather slender and fusiform oxea: 110-150 x 3-7.5 µm (cf. table below).
Skeleton: (Haliclona viscosa skel) There is no ectosomal skeleton, but spicules of the primary lines project through the dermal membrane (Haliclona viscosa skel2). Choanosomal skeleton rather close meshed, with pauci-multispicular primary and unispicular secondary lines and with many spicules in confusion. The interior of the sponge is frequently built up by lines which are arranged in different directions. There are many choanosomal spaces. Spongin: scarce, confined to the nodes of the spicules.
Ecology: In the infralittoral, to 50 m, on vertical or horizontal sides of rocks in places with strong currents and low turbidity.
Distribution: Shetland Islands, British Isles, Belgium, France, Portugal, Mediterranean.
Etymology: The name refers to the consistency.
Type specimen information: Holotype: MNHN D.T. 3043, Luc (Calvados), France.

Remarks

Haliclona (Rhizoniera) viscosa is well characterized by its rather uniform shape and slimy consistency. Among the chalinids of the study area it is one of the most constant, and thus easily recognizable species. The form is always thickly massive (Haliclona viscosa MCS2) with oscules placed at the top of chimney-or volcanoshaped elevations (Haliclona viscosa BandW). The tendency to have the oscules (Haliclona viscosa MCS4) placed in rows is observable even in young, small specimens (Haliclona viscosa MCS3). The ridges are almost always present. This stability holds true also for the colour, consistency, skeletal architecture, size and shape of the oxeas and the amount of spongin. Furthermore the species is ecologically characterized by its preference for bare rock faces in places with strong currents and low turbidity.
The surprisingly few records of this common species may be explained by its occurrence in deeper water in places which require either SCUBA-or special dredging equipment. A positive result of low variability of H. viscosa is the stability of its taxonomic status. Apart from one of Bowerbank's specimens of Isodictya indistincta, which most probably belongs to H. (R.) viscosa, and Descatoire's (1969a, b) misinterpretation of the sponges found at the Iles de Glénan, which she partly identified as Reniera indistincta and Reniera viscosa, and partly described as a variety of R. viscosa, there are no other species names confused with H. (R.) viscosa. It is not exaggerated to say that this is a rarity for the haplosclerids of the study area.
H. viscosa is closely related to Haliclona (Rhizoniera) indistincta (Bowerbank, 1866) and Haliclona (Rhizoniera) rosea (Bowerbank, 1866). Topsent (1888), who evidently misinterpreted H. (R.) rosea (cf. de Weerdt and Stone, 1987), mentioned the close relationship between H. viscosa and H. (R.) indistincta, but left H. (R.) rosea out of consideration. According to him the first two species share spherical cells which are filled with "amidon", and the production of mucus. Topsent did not mention the high similarity in skeletal architecture, which is very obvious. According to Topsent the differences between H. viscosa and H. (R.) indistincta were: the massive habit of H. viscosa and the encrusting habit of H. (R.) indistincta; the colour, which is orange-brown in H. (R.) viscosa (more purple according to my observations), verging to black under suboptimal conditions, and greyish in H. (R.) indistincta, the oxeas, which are slightly larger in H. (R.) viscosa than in H. (R.) indistincta (this difference is minimal, both species overlap completely), and the ecology: H. (R.) viscosa occurring deeper than H. (R.) indistincta which is confined to the infralittoral fringe zone.

Spicule sizes of specimens studied by De Weerdt, 1986: Spicule sizes H. viscosa.

Description of individual specimen:
ZMA POR. 5555 from Iles des Glénans, W coast of France, consists of six larger specimens and a few smaller fragments. The largest specimen is massive, somewhat laterally compressed, 7 x 4 x 4 cm. At the upper side there are nine oscules of 2-4 mm; they are linearly arranged. The sides of the sponge are roughly undulating by the presence of grooves. The other specimens are smaller, but similar in habit.
The sponge pictured in De Weerdt's (1986) pl I fig. 2 is a laterally spreading crust from which arise numerous partly isolated, partly fused tube-like elevations, each with an osculum at the summit.
Source: De Weerdt, 1986

Haliclona viscosa