Antho inconstans Topsent, 1925


Family : Microcionidae

Form: Thin sheet forming extensive patches on rock surfaces or on other sponges (e.g. Stelletta grubii).

Colour: Orange-red.

Smell: None.

Consistency: Fairly tough sheet, which holds together well when scraped off.

Surface: Lumpy and irregular, with a slightly velvety appearance, similar to Microciona spinarcus.

Apertures: Oscules inconspicuous, scattered, irregular in shape and size. Excurrent channels are generally conspicuous, converging on the oscules and forming irregular stars.

Contraction: None to slight.

Internal characters

Skeleton: An anisotropic reticulation, with a triangular or quadrangular mesh of megascleres (acanthostyles) of varying sizes, quasi-echinated by smooth megascleres at the internodes of the net. Longer smooth megascleres (styles) pierce the surface, but these are much shorter than the corresponding spicules in Antho involvens. Fine accessory ectosomal spicules are present.

Spicules: Megascleres of the main skeleton are acanthostyles (b) and acanthostrongyles (c). The acanthostyles have a region of denser spination near the head and near the tip, and the smooth point itself is very short and abrupt. They are typically ca. 135-155μm in length. Smooth ectosomal styles (a) ca. 200μm in length, slightly fusiform with a constriction above the head. The accessory spicules are fine subtylostyles (d) (sometimes styles) with microspined heads (this may not be visible with a light microscope). Microscleres are palmate isochelae (f) (ca. 17μm), which may be rare, and toxa (e), which may be abundant.

Habitat: Vertical or steeply inclined rock faces in both sheltered and exposed places. May be on other sponges such as Stryphnus ponderosus and Stelletta grubii.

Distribution: "South coast of England; France; Spain; Mediterranean etc." Known recently from Lough Hyne, Co. Cork; W. Anglesey; Skomer; N. Cornwall; Jersey; Guernsey.

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

Identity: Many Clathriids form red sheets, but the spicule complement is quite different from that of Microciona spp. The characters given here and for Antho involvens should distinguish these two species, which have often been synonymised in the past. Antho inconstans is easily confused with Plocamilla coriacea (Bwk 1874:228), which forms bumpy sheets and may also grow on other sponges, indeed the two species can be found growing alongside each other. Acanthostrongyles are the predominant megascleres of the main skeleton in Plocamilla, and the acanthostyles do not show the band of spines near the tip as in Antho inconstans, looking more like those in Antho involvens. Otherwise the spicule complement is similar for these three species (with slight size differences).

Voucher: BELUM : Mc1349. Skomer Island.

Editors: D. Moss, B.E. Picton.

 Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland