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(Linnaeus, 1767)

Species Overview

Suberites ficus (Linnaeus, 1767) is a big massive lobate, occasionally cylindrical, orange sponge with one or more conspicuous, large oscules. It feels firm, but contracts visibly when prodded. It has a velvety smooth appearance. Growth forms may include specimens enveloping gastropod shells and encrusting scallops. It differs from several other species of Suberites in the possession of centrotylote microrhabds (microscopical examination necessary). Occurs mostly in places with tidal currents.

Taxonomic Description

Colour: Usually orange, sometimes intermediate shades of yellow, orange or brown. It has been reported as white, white-grey, grey or green (the latter in patches, caused by the presence of symbiotic algae). The interior is yellow.
Shape, size, surface and consistency: (Suberites ficus MCS1) (Suberites ficus MCS2) (Suberites ficus MCS3) Varied. It may be a cushion, massive-lobose, massive-globose, or cylindrical. The massive-lobose form is typical, but growth forms include specimens encrusting or enveloping mollusc shells. Size variable, 10-40 cm in length. Surface smooth, not velvety (cf. S. carnosus), but presents high friction when the tongue is run over it. Hirsute, even, with an 'open' appearance when alive. One to many (5, or even more) large oscules (up to 5 cm diameter), mostly at the tops of the lobes but other positions are possible. Consistency firm, moderately elastic, softer when undisturbed in water. Elongate forms break when bent through 20 degrees. Contraction noticeable: when removed from the water the sponge contracts to about 3/4 of its size when undisturbed underwater. Smell faint, of freshly cut cucumber.
Spicules: (Suberites ficus spics) Megascleres are tylostyles of 2 sizes (100-250 µm and 350-500 x 5-10 µm), the larger growing in a wide size range (cf. S. carnosus). Microscleres are microrhabds (smooth or microspined microxeas or microstrongyles, often centrotylote), often rare and needing careful searching of the ectosome, amongst the tips of the palissade spicules (i.e. right at the surface). Size 15-50 µm.
Skeleton: Subradiate, the radial arrangement of the spicules being most apparent near the surface. Internally the skeleton is confused, almost halichondroid. There is one category of spicule (tylostyle), divided into two size groups. The larger constitute the main structural megascleres, whereas the smaller are perpendicularly arranged as a dense palisade at the surface.
Gemmules: These may be found in the basal parts of the sponge encrusting the substrate.
Ecology: Sheltered waters, usually where there are tidal currents, although can be found in still water. On rock, wreckage (when it may hang down into the current), sometimes growing around empty gastropod shells inhabited by hermit crabs, and on Chlamys valves. In still water it sometimes occurs free-living, having initially settled on a piece of hard debris which is subsequently enveloped.
Distribution: Widespread throughout Arctic and Atlantic.
Etymology: ficus (Latin) = fig, presumably referring to the shape.
Type specimen information: No type material in BMNH.

Remarks

The name given to the species is still tentative, because the specific distinctness of Suberites ficus and other named forms needs further study. Both massive and enveloping/encrusting forms have the centrotylote microrhabds, but these are found in Suberites species elsewhere in the world, so that may not be considered evidence of conspecificity.
Suberites suberia has been considered a synonym of this species; it is enveloping gastropod shells inhabited by hermit crabs) and recent research (Solé-Cava et al., 1986 as S. pagurorum) has shown that it is genetically distinct.
An encrusting form has been called S. farinaria, but no further research has been done on that, so we tentatively consider it a juvenile growth form of the present species.
A further commonly assigned synonym is Suberites virgultosa which has an elongated wedge-shaped form; it is especially common in North Sea sand habitats and in view of the fact that is never shows any larger oscules, we consider it a separate species.
With all these species there are taxonomic as well as nomenclatorial problems: the name ficus goes back to Pallas (1766 as Alcyonium), but that is generally assumed to have been a compound ascidian. Subsequent uses of the name ficus by Linnaeus (1767), Esper (1794) and Lamarck (1814) were likewise uncertain. Only when British authors (Johnston, 1842, Bowerbank, 1866) used these names in combination with descriptions of the spicules, the names became more profiled. We propose here to retain Suberites ficus authored by Linnaeus (1767) as the proper name for the present species for the time being until a proper revision has been made.
Two other species of Suberites are commonly reported from the Eastern Atlantic, viz. S. carnosus (Johnston, 1842) and S. domuncula (Olivi, 1791). The first of these is very common; it is compared with the present species below. The latter is a "mobile" sponge, always occupied by hermit crabs. It is uncertain whether typical domuncula occur in our area; they may be easily confused with S. suberia, and only microscopical examination will tell.
The two common species of Suberites are S. ficus and S. carnosus. The table below sets out the differences between them. Before coming to a conclusion, make sure that all the characters fit. The presence of centrotylote microscleres in S. ficus needs to be treated only as a useful confirming character.

Differences between S. carnosus and S. ficus (based on criteria communicated by S.M. Stone): S. carnosus & S. ficus.
Sources: Topsent, 1900; Ackers et al., 1985 (D. Guiterman, S.M. Stone, D. Moss).

Suberites ficus