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(Johnston, 1842)

Species Overview

Haliclona (Haliclona) simulans (Johnston, 1842) may form flat smooth crusts, cushions, repent branches and upright bushes with irregularly anastomosing branches. The colour is beige-brown, frequently with reddish brown "discolourations". The consistency is characteristically corky, firm to hard. Oscules are numerous, slightly elevated, and do not collapse or contract when lifted out of the water or in preservation. Occasionally specimens form distinct tubular elevations. Common under stones (flat crusts) and on rocks from the intertidal downwards to 30 m.

Taxonomic Description

Colour: Various shades of brown, dark yellow, orange and grey. Most frequently there are several different coloured areas adjacent to each other (Haliclona simulans close up), with a sharp boundary. The areas around the oscula are often whitish.
Shape, size, surface and consistency: Extremely polymorphic. At the underside of intertidal stones it grows as thin, flat encrustations with small circular oscules which are slightly elevated or flush with the surface (Haliclona simulans BandW 1). It may form large, laterally spreading masses, from which arise osculiferous, and also branching elevations (Haliclona simulans Mario 2). Oscules chimney-and volcano-shaped. The sponge may also be repent ramose (Haliclona simulans Mario 1), forming bushes of branches (Haliclona simulans BandW 2) which fuse at irregular distances and which are intermittently attached to the substratum. The osculiferous elevations may, in extreme cases be so large as to become thick-walled tubes which end in a wide osculum (Haliclona simulans BandW 3). Commonly the number of oscules is rather high; they are situated at regular distances on the encrusting basal part and they are very regularly distributed on all sides of the branches. The area directly around an osculum is frequently somewhat swollen, especially in the branched and tube-like forms. The size varies from a few centimetres in diameter in the encrusting forms to 20-30 cm in the branched forms (Haliclona simulans branch). Surface: smooth and even, in places slightly hispid. Consistency: very firm and incompressible, corky.
Kaandorp (1994) modelled the growth form of this species using fractal geometry methods.
Spicules: Short, fat, cigar-shaped oxeas, with rather short and sharp points: 130-155 x 8-11 µm (see also table).
Skeleton: Ectosome (Haliclona simulans ectodraw): a strong, very regular, unispicular and isotropic, tangential reticulation of oxeas. Frequently the oxeas intercross (Haliclona simulans ectophoto). Choanosome (Haliclona simulans skeleton): a rigid, rather close-meshed skeleton of straight paucispicular primary lines which are connected by single or double secondary spicules at regular distances. Many choanosomal spaces. Spongin: moderate to abundant, yellowish, clearly visible. Always present at the nodes of the spicules, but it becomes very abundant towards the interior. Here it forms thick fibres which are enclosing the spicules entirely.
Reproduction: Data on reproduction are provided by Topsent (1888), Delage (1892) and Lévi (1956), summarized in Wapstra and Van Soest (1987). The larvae are whitish with red-brown posterior pole. They have a ring of longer cilia around the posterior pole and their posterior pole is bare (usual for the Chalinidae), the shape is oval to elongate, and there are embryonic spicules present in them.
Ecology: Under intertidal stones and in the infralittoral, to 30 m. In sheltered microhabitats, although the sites are often quite exposed, with appreciable current. Rather common.
Distribution: British Isles, Channel Islands, France, Portugal, reaching south to the Mediterranean, Madeira and the Canary Islands.
Etymology: The name refers to the polymorphic growth form.
Type specimen information: Lectotype: BMNH 1847:9:7:9, Britain, figured specimen of Johnston, 1842: pl. VIII fig. 5 (per De Weerdt, 1986: 66)

Remarks

Haliclona (Haliclona) simulans is well characterized by its firm consistency, the different coloured areas within the same individual, and by its skeletal characteristics.
The conspecificity of Isodictya densa, Isodictya pallida [the majority of the specimens in the BMNH collection belong to H. (H.) simulans, a few however appeared to be H. (Reniera) cinerea (Grant)], Isodictya ingalli, Halichondria condensa and Siphonochalina crassa is certain. The established synonymy of the species is based on a thorough comparison of all the original specimens.
The conspecificity of Bowerbank's species (Isodictya simulans and densa) with H. (H.) simulans needs no further discussion here; all specimens fall within the range of the most common growth forms, viz. encrusting patches, patches with elevated oscules, and repent ramose branching forms. They are all of the firm, corky consistency of H. (H.) simulans and they have the characteristic skeletal architecture. The spicule sizes of a selection of specimens is given in the table.
The conspecifity of the Mediterranean species Siphonochalina crassa Topsent, 1925b with H. (H.) simulans may need some explanation here. Topsent (l.c.: 713) described the species from a specimen identified by Schmidt as Siphonochalina coriacea Schmidt (1868), but which he considered as a different species. This specimen was branched, firm, and with robust, slightly curved and shortly pointed oxeas of 160-190 by 8-10 µm. Topsent recorded S. crassa as a common species in the Gulf of Naples. The here studied specimens of S. crassa are from the Iles de Glénan (south Bretagne); both specimens consist of large, thick-walled tubes which end in a wide osculum. That this form occurs in northern representatives of H. (H.) simulans is demonstrated by the specimen GA 266 (Haliclona simulans BandW 3); this sponge is a smaller representation of Topsent's specimens of S. crassa. The form is not a common one, but the figured sponge proves that it does exist. The firm consistency, the different coloured areas and the skeletal characteristics leave no doubt about the identity of Topsent's material and the figured specimen.
Griessinger (1971: 126) described Topsent's species, as Reniera crassa and treated H. (H.) simulans, as Adocia, in the same paper (l.c.: 158). It is hard to understand why he assigned the two species to different genera. In his description of R. crassa he mentioned the high similarity of this species with tubiform specimens of Adocia simulans. As only difference and as a characteristic feature of R. crassa he mentioned the spicule brushes projecting through the surface. H. (H.) simulans varies somewhat in the degree of hispidity; it may be rather hispid in some places (caused by protrusion of the primary lines through the surface) and entirely smooth in other places. The studied specimens of Siphonochalina crassa showed a similar variation in the degree of hispidity.
H. (H.) simulans is related to the Mediterranean species Adocia (=Haliclona) varia Sarà, 1958b, Adocia (=Haliclona) reptans Griessinger, 1971, Adocia (=Haliclona) laevis Griessinger, 1971, and Adocia (= Haliclona) cribrata Pulitzer-Finali, 1983. H. (H.) simulans is most similar to H. (H.) varia. Sarà (1958b: 267, pl. 11 fig. G, fig. 26 a-c) described this species from the Gulf of Naples as a branched, lobate sponge with circular oscules of 1 mm, with a regular tangential ectosomal skeleton, with a paucispicular choanosomal skeleton, and oxeas of 100-118 x 4-7 µm. Many centrotylote oxeas, styles and strongles were intermixed. Sarà's material was not re-eaxamined, but instead a microscopical slide of Griessinger's material of the species, described from the Adriatic and Banyuls could be studied. The fragment of which the slide was made was strikingly similar to H. (H.) simulans, as far as the form (one lobate osculiferous fragment) and the consistency are concerned. The colour was greyish. The skeletal architecture, especially of the ectosome was very similar to H. (H.) simulans: the ectosomal skeleton consisted of a reticulum of intercrossing oxeas; the choanosome was paucispicular. The oxeas are ca. 122-132 x 5 µm. As only difference there was very little spongin in Griessinger's material of H. (H.) varia, which agrees with Sarà's description. Tentatively H. (H.) simulans and H. (H.) varia are considered conspecific.
H. (H.) simulans differs mainly from H. (H.) reptans by the much smaller oxeas of the latter species, viz. ca. 90 x 5 µm; the same holds true for H. (H.) laevis, which is indistinguishable from H. (H.) reptans. From both species the type specimens, which are stored in the MNHN have been re-studied.
The difference between H. (H.) simulans andH. (H.) cribrata is the more fragile consistency of the latter species, and its much smaller and fusiform oxeas (60-100 x 2.5-4.5 µm, according to Pulitzer-Finali, 1983: 583). In addition, H. (H.) cribrata has little spongin.

Table of spicule sizes of various specimens considered to belong to H. (H.) simulans: Spicule sizes H. simulans.

Description of type material:
The lectotype of Halichondria simulans, BMNH 1847.9.7.9, consists of a rather thin, flat base of 5.5 x 2.5 cm with one pronounced volcano-shaped elevation and two smaller ones. The larger elevation is ca. 2 cm high. There are a few small, circular, not elevated oscules at the basal part of the sponge, and at the top of the smaller elevations. The large elevation ends blind but has two small oscules halfway. The diameter of the oscules is ca. 2 mm. The colour is brown (dried) and the consistency is very firm. The surface is smooth. The ectosomal skeleton is a regular tangential, unispicular reticulation of oxeas, which partly intercross and which are connected by spongin at the nodes. The choanosomal skeleton is a strong reticulation of pauci-multispicular primary lines, regularly connected by unispicular secondary lines. The oxeas are cigar-shaped and measure 129 x 7.8 µm (see also table in which the spicule sizes of a selection of specimens are given).
The lectotype of Isodictya pallida is a flat patch, 2.3 x 1.3 x 0.3 cm, growing on a solid conglomerate of tube worms and calcareous algae. There are three circular oscules flush with the surface, ca. I mm in diameter. The colour (dried) is light yellowish-brown, the consistency very firm and the surface smooth. The ectosome is again a rigid, isotropic reticulation of spicules which partly intercross and which are at the nodes connected by spongin. The choanosome is a strong, dense reticulation of pauci-multispicular primary lines, regularly connected by unispicular secondary lines. There are many choanosomal spaces. The oxeas are cigar-shaped and measure 136 x 8.8 µm.
The lectotype of Isodictya ingalli is laterally branched, fully corresponding to Bowerbank's figure (Bowerbank, 1874, pl. LXXVIII fig. 1). The colour is light yellowish-brown, the consistency very firm and the surface smooth. The skeletal architecture and shape of the oxea is the same as the other specimens. The oxeas measure 144 x 8.6 µm.
MNHN D.T. 2944, Siphonochalina crassa consists of one, coarse tube ending in a wide osculum. The colour (spirit) is yellowish-brown, and the consistency very firm. The skeletal architecture is completely similar to Johnston's and Bowerbank's specimens. The oxeas measure 153 x 9.4 µm.
ZMA POR. 5549 (see figure) is a bush of partly fused branches, which are 0. 5-1 cm thick. A few branches have broken off but the remainder of the bush is 18 cm high, and ca. 8.5 cm at its largest breadth. It consists of 10 branches, which originate from two basal branches; these were attached to the substratum with a small base. The oscules are circular, some of them with a slightly elevated rim, 1-2 mm. They are situated on all sides of the branches at regular intervals; the area around the oscules is swollen. The colour (spirit) is light yellowish, with darker coloured areas.
Source: De Weerdt, 1986

Haliclona simulans