Marine Species Identification Portal : Clathria strepsitoxa

(Hope, 1889)

Species Overview

Clathria (Microciona) strepsitoxa (Hope, 1889) is one of the red encrusting Microcionids which are indistinguishable on sight. Microscopic recognition of this common species is fairly easy on account of its long, thin, straight toxas with only a very small median inflexion which may easily become twisted. It is a southern species occurring from the British Isles southwards to the Azores and in the Mediterranean.

Taxonomic Description

Colour: Red, orange-red.
Shape, size, surface and consistency: Thin crust, to > 20 cm2. Surface conforms closely to underlying substrate. Excurrent channels often clearly visible. Oscules large, distinct, with slightly raised rims, at centre of system of conspicuous, convergent, sub-surface channels. Contraction hard to determine. Fragments tend to curl up in alcohol (which becomes orangeish). Consistency hard to determine; comes away in scraps.
Spicules: (Clathria strepsitoxa spics) Megascleres: Ectosomal subtylostyles may have rugose or very lightly spined heads: 150-500 x ca. 2-5 µm. Principal megascleres are acanthostyles, perhaps slightly curved, with spines at the head only (these spines may be almost invisible): 350-700 x 5-7 µm. Echinating acanthostyles are straight to slightly curved, and covered with spines: 70-200 x 4-6 µm.
Microscleres: Palmate isochelae: 12-20 µm (in the Mediterranean: 11-15 µm according to Lévi, 1960) and toxas of two types: with large central flexion: ca. 40-140 µm, and with a very small, somewhat twisted, central flexion: ca. 200-460 µm.
Skeleton: Typically microcionid (see C. (M.) atrasanguinea). According to Lévi (1960: 67) there is some tendency for the longer principal megascleres in the plumose columns to be found towards the surface.
Ecology: Vertical rock surfaces in regions of considerable water movement. Also Aequipecten valves, stones, etc. Littoral, infra-and circalittoal.
Distribution: British Isles, Atlantic coasts of France, Spain, Mediterranean, Azores.
Etymology: strepsis (Greek) = a twist or turn, referring to the central twisted flexion of the toxas.
Type specimen information: The type is in the Natural History Museum, London. MCS voucher BELUM: Mc1743, Calf, Isle of Man.

Remarks

Difficult, if not impossible, to separate visually from various other ''red crusts". The conspicuous star-like arrangement of channels converging to the oscules (best seen in close-up photographs) may give a clue. Microscopically the presence of large toxas with a small twisted, central flexion is distinctive, though some other Clathria (Microciona) species (C. ascendens and C. osismica) share this feature. But these have other differences, cf. descriptions of these species. Occasionally, in aberrant specimens the isochelae may be scarce.
Sources: Lévi, 1960; Ackers et al., 1992 (D. Moss, B.E. Picton)

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Clathria strepsitoxa