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(Montagu, 1818)

Species Overview

Amphilectus lobatus (Montagu, 1818) forms small cushions on other organisms such as algae and hydroids. It is similar in consistency and skeletal characteristics to A. fucorum, but differs in being beige-yellow (not orange) and having microscleres (microscopic examination necessary) that are anisochelae (not or rarely isochelae). It is a boreal-arctic species reaching its southern limit in Wales.

Taxonomic Description

Colour: Pale yellow, beige.
Shape, size surface and consistency: Round, egg-shaped, or flattened cushions growing on brown algae, hydroids or erect bryozoans, 4-15 mm in diameter. Larger specimens are cylindrical or rather irregular in shape as a result of growth along the branches of the substrate organism and coalescence of originally separate individuals. Surface very finely hispid. On small cushions there is a single oscule, flush with the surface; larger specimens may have oscules in rows along a ridge, or somewhat scattered. Contraction not noticeable. Smell: strong, pungent, "garlic", like Halichondria (Halichondria) panicea. Consistency slightly elastic, very soft.
Spicules: (amphilectus_lobatus_spics.jpg) Megascleres: more or less curved styles, the curvature occurring nearer to the rounded end of the spicule. They are slightly thicker in the middle region (fusiform) and slightly constricted just above the head. Lengths are 145-(190)-230 µm (up to 310 µm in some specimens), widths of 2-4 and 7-10 µm (even 11 µm sometimes). Microscleres: Anisochelae variable in size, from 15-23 µm in length. They also vary greatly in the relative sizes of the chelate ends. In some specimens the difference between the ends is so slight as to suggest isochelae, but usually the size difference is considerable. In some specimens considered to be the same species the anisochelae can be up to 45 µm in length.
Skeleton: Primary polyspicular bundles, cross-linked here and there by single spicules, run from the substratum to the surface. The arrangement may be somewhat confused basally, but becomes more uniform near the surface. In the primary bundles (in which 6-8 spicules may be closely set side by side) the spicules all have their pointed ends in the direction of the surface. The primary bundles may curve along their lengths. The transverse interlinking spicules are also styles. The dermal membrane is largely clear of styles, but contains scattered anisochelae. Spongin is not obviously abundant, and is colourless.
Ecology: Almost always found on weeds, hydroids, erect bryozoans, in low-lying littoral rock pools and in the infralittoral zone to 200 m depth; usually in strong water movement. May be common coating the basal portion of the hydroids Hydrallmania falcata and Sertularia argentea in tidal streams of 3-7 knots. Often found in rias and sea loch entrances.
Distribution: North Atlantic and North Sea: Ireland, SW England, Wales, Faroe Isles, Wadden Sea, Kattegat, Norway, Iceland, Greenland, Baltic Sea, White Sea.
Etymology: the name refers to the habit.
Type specimen information: Type in Natural History Museum, London: slide "spicula from the Type with Dr. Grant. Devon Coast." Unregistered (Bk.952). Bowerbank Collection. MCS voucher BELUM: Mc1838, Milford Haven, Pembroke, Wales.

Remarks

A spicule preparation or thin section of the sponge is required. The variable anisochelae and the smooth styles are diagnostic. There might be confusion with Amphilectus fucorum, but in this species the microscleres are isochelae, the skeletal arrangement is more regular and usually the colour of the sponge is reddish-orange.
Sources: Lundbeck, 1905: 34 (as Mycale ovulum), Ackers et al., 1992 (W.C. Jones, G. Ackers, B.E. Picton, D. Moss).

Amphilectus lobatus