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Burton, 1930b

Species Overview

Halichondria (Halichondria) bowerbanki Burton, 1930b is a shallow subtidal, occasionally intertidal yellowish beige sponge with characteristically stringy appearance. Long, string-like projections issue from a thinly encrusting base. No apparent oscules. Texture like crumb-of-bread, soft. Confused skeleton of oxeas only. Sister species to the common crumb-of-bread sponge and easily confused with less typical growth forms of that species, but absence of chimney-type oscules and less uniformly confused tangential ectosomal skeleton suffice to tell them apart. Less common, but largely overlapping in ecological and geographical range.

Taxonomic Description

Colour: Beige or dull brownish grey in summer, light grey yellow or whitish in winter. Specimens about to spawn their larvae are often characteristically yellow-orange due to colour of larvae. Greenish shades are rarely encountered.
Shape, size, surface and consistency: Growth form variable (Halichondria bowerbanki JZ), thinly to somewhat massively encrusting, with long outgrowths (Halichondria bowerbanki France), irregular tassel-like branches (Halichondria bowerbanki MCS) which anastomose to form irregularly flattened masses. Occasionally bush-like (Halichondria bowerbanki BandW). Size up to 25 cm across and branches may reach12 cm. Surface smooth or uneven, often with a translucence. Parchment-like skin. Consistency soft, compressible. Texture crumb-of-bread like. Oscules inconspicuous, at the base of branches, opening irregular, mostly small (1-2 mm), but occasionally larger (up to 5 mm), then with irregular rim (Halichondria bowerbanki MCS2).
Spicules: (Halichondria bowerbanki spics) Oxeas, relatively long and thin, tapering very gradually towards the apices: 133-570 by 2-16 µm. Average sizes are 375 by 6 or 385 by 11 µm. No statistically significant difference between ectosomal and choanosomal oxeas has been found.
Skeleton: Ectosomal: tangential (Halichondria bowerbanki ectosom), with paucispicular bundles intercrossing, and lying at some distance from each other, giving a more open reticulated aspect. Choanosomal: confused, with ill-defined paucispicular dendritic bundles ending at the surface at various angles. No visible spongin.
Reproduction: This is a viviparous species. The parenchymella larvae are yellow-ochre coloured, darker than those of H. (H.) panicea, completely ciliated, with a posterior tuft of larger cilia (Wapstra and Van Soest, 1987). Life history: The species is hermaphroditic; the reproductive period is distinctly later in the year than that of H. panicea: late summer and fall, with first larvae appearing only in July-August and continue to be produced until November (Vethaak et al., 1982; Wapstra and Van Soest, 1987).
Ecology: Sheltered environments, under overhanging rocks in sediment rich environments. Although it overlaps broadly with H. (H.) panicea, it may occur in muddy environments where H. (H.) panicea cannot survive. It is less resistant towards desiccation and thus is found only in the lowest part of the intertidal. It grows often intertwined with hydroids and algae.
Distribution: More or less the same as that of H. (H.) panicea, on both sides of the Atlantic, penetrating far to the south along the coasts of the Eastern United States, e.g. it is reported from North Carolina. On the European coasts it is reliably reported southwards until Bretagne. Morphologically similar specimens are found along the west coast of Africa and in the Mediterranean, but need revision. Records from other oceans are likewise unreliable.
Etymology: Named after James Scott Bowerbank (1797-1877), pioneering author of the W European sponges.
Type specimen information: The type is in the Natural History Museum, London: BMNH 1938.6.30.32a? (Bowerbank's specimen of Halichondria coalita Halichondria bowerbanki drawing). MCS voucher BELUM MC150, Strangford Lough, N Ireland.

Remarks

The variable nature of Halichondria (H.) bowerbanki and H. (H.) panicea can make it very difficult to identify individual specimens. Typical growth forms, however, are easy to recognize: H. (H.) bowerbanki is irregularly branched with long string-like projections, H. (H.) panicea is compact with clearly recognizable regular oscular chimneys. Below a table of differences between the two species is given. Other species in the area with long and thin oxeas, which may be occasionally confused with the present species are Halichondria (Eumastia) sitiens which has clear papillae (resembling a whitish Polymastia) and Spongosorites spp. which which are much more compact and harder.

Differences between Halichondria (H.) panicea and H. (H.) bowerbanki: H. panicea & H. bowerbanki.
Sources: Vethaak et al., 1982; Ackers et al., 1992 (S.M. Stone, D. Moss, B.E. Picton)

Halichondria bowerbanki