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(Schmidt, 1864)

Species Overview

Antho (Antho) involvens (Schmidt, 1864) is another of those red encrusting microcionids which can only be distinguished from other similar species by making a microscopic slide of spicules and skeleton. It differs from most encrusting microcionids in having an isotropic recticulate skeleton; it differs from other encrusting Antho species in lacking any acanthostrongyles and by a smooth (rather than a bumpy) surface. This is a southern species, reaching its northern limits on the south coasts of the British Isles.

Taxonomic Description

Colour: Watery orange to bright red.
Shape, size, surface and consistency: Thin sheet (Antho involvens V) forming extensive patches on rock surfaces. In encrusting form it can be easily detached from the substrate. The literature claims it can become branched-erect, sometimes stalked, but we consider this to refer to a separate species. Surface smooth, slightly hispid. Oscules conspicuous, spaced regularly across the surface, with slightly raised conical rims; circular and consistent in size. Ostia apparent on close examination. Excurrent channels are inconspicuous, not at the surface of the colony, but their ends are visible inside the oscules. Consistency: fairly tough sheet, which holds together well when scraped off. Contraction none to slight.
Spicules: Megascleres: (Antho involvens spics) Ectosomal spicules are fine styles or subtylostyles with microspined heads 330 x 4 µm. Megascleres of the main skeleton are subectosomal styles: ca. 500 µm, acanthostyles (never acanthostrongyles), entirely but often sparingly-spined: typically 145-160 µm in length.
Microscleres: Palmate isochelae: ca. 17-23 µm, which may be rare, and toxas, which may be abundant: ca. 65 µm.
Skeleton: An anisotropic reticulation, with a triangular or quadrangular mesh of megascleres (acanthostyles), of varying sizes, many sparingly spined, often quasi-echinated by smooth megascleres at the nodes of the net. Long smooth megascleres (styles) pierce the surface. Fine accessory ectosomal styles are present.
Ecology: Vertical or steeply inclined rock faces in both sheltered and exposed places.
Distribution: South coast of England, N coast of Ireland (recorded recently from Skomer, Rathlin Island), France, Spain; Mediterranean. Confusion with Antho (A.) inconstans leaves previous records in doubt.
Etymology: involvens = wrapping-up, referring to the encrusting habit.
Type specimen information: Type material in the Leiden Museum. MCS voucher BELUM Mc1363, Skomer Island. Wales.

Remarks

Many Microcionidae form red sheets, but the spicule complement of Antho spp. is quite different from that of Clathria (Microciona) spp. Antho (A.) involvens is also easily confused with Antho (Acarnia) coriacea, which forms bumpy sheets and may also grow on other sponges. Acanthostrongyles are the predominant megascleres of the main skeleton in A. (A.) coriacea, otherwise the spicule complement is similar for both,
Source: Lévi, 1960; Ackers et al., 1992.

Antho involvens