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(Pallas, 1766)

Species Overview

Halichondria (Halichondria) panicea (Pallas, 1766) is an intertidal or shallow-subtidal, thickly encrusting, massive or occasionally branching sponge, with typical volcanoe-shaped oscular chimneys. Colour green or yellow. It emits a characteristic disagreeable smell, said to be similar to that of "carbide". Surface smooth. Consistency firm, texture crumb-of-bread (hence its popular name "crumb-of-bread sponge" and its latin name "panicea"). Ectosome detachable. Spicules oxeas only. One of the commonest intertidal sponges of North West Europe, but occurring all over the Holarctic region.

Taxonomic Description

Colour: Basically light orange-yellow or pale yellowish green. However, intertidal specimens exposed to the light may be dark greyish green, presumably due to microsymbionts.
Shape, size, surface and consistency: Quite variable in shape, related to exposure to water movement. Specimens growing in intertidal localities exposed to the full oceanic surf may be entirely smooth (Halichondria panicea MCS3) with barely visible oscular chimneys (Halichondria panicea MCS2). More intermediate environments show the typical volcanoe-shaped chimneys (H.panicea watercolour) up to 4 or 5 cm high. Oscules are relatively large, conspicuous, 2-4 mm in diameter. Sponge body may be up to 25 cm thick and 60 cm across, but much smaller specimens are the rule. In localities with strong currents specimens may grow out to form longer oscular chimneys (Halichondria panicea MCS4) closely adhering and verging toward palmate forms. In deeper or stagnant waters, with absence of wave surge, specimens may form masses of anastomosing branches (Halichondria panicea Holland), with oscular chimneys here and there on the branches. Consistency is firm, compressible, easily torn.
Spicules: (Halichondria panicea spics) Oxeas only; size in specimens from Western Europe: 124-482 by 2-15 µm. Average sizes are: 300 by 7 µm(Holland), 280 by 8 µm (France), 360 by 9 µm (Ireland). Several authors report a subtle but statistically significant difference in spicule lengths between ectosomal (shorter) and choanosomal (longer) spicules, but no definite size categories can be distinguished due to large overlap.
Skeleton: Ectosomal (Halichondria panicea ectosome): is tangential (as is usual for the genus), with spicules arranged disorderly or in tight bundles, leaving very little open space for ostia (see figure). Specimens in exposed localities have thicker and more organized ectosomal skeletons (a separate species H. reticulata has been distinguished for that reason by various authors). Choanosomal: largely confused, but near the surface some organization into tracts is observed in many specimens. These tracts carry the ectosomal reticulation, leaving large subectosomal spaces between them. There is very little visible spongin.
Reproduction: This is a viviparous species; larvae have been observed by many authors: e.g. Topsent, 1911; Hartman, 1958a; Wapstra and Van Soest, 1987 (SEM photos). They are orange-yellow, oval to oblong, ciliated uniformly, but with a posterior tuft of longer cilia; size up to 600 by 180 µm. Life history: conflicting observations have been made about the sexual cycle of this species. Sponges in Holland were found to be hermaphroditic (Wapstra and Van Soest, 1987), those in the Baltic gonochoric (Witte and Barthel, 1994). Reproductive periods are April to September, with larvae being released from June to September.
Parasites: Sometimes parasitized by the alga Tribonema endozooticum (Wille) (Borojevic et al., 1968).
Ecology: This species occurs in the intertidal region as well as in the sublittoral down to more than 500 m. In the intertidal region it occurs on upper, lateral and undersides of boulders and holdfasts of brown algae. It is the commonest intertidal sponge of the Eastern Atlantic. In the sublittoral it is likewise common, especially in northern areas, e.g. the coasts of the North Sea. Vethaak et al. (1982) established that its tolerance towards siltation is lower than its sympatric sister species H. bowerbanki, preferring somewhat more exposed habitats. However, the ecological range is broad and overlaps considerably with that of H. (H.) bowerbanki.
Bacteria causing decay and death of this species were studied by Hummel et al. (1988). Ecophysiological aspects such as substrate specificity, growth, biomass, production and energy budget were studied by Barthel (1986; 1988; 1991). Production of faecal pellets was measured by Wolfrath and Barthel (1989). Riisgård et al. (1993) measured the rate of suspension feeding of this species determined its energy costs at different temperatures.
Forester (1979) studied the association between this species and scallops (Chlamys varia). The scallops allow bread-crumb sponges to overgrow their shells in order to escape predation by starfishes; the sponge receives increased nutrient supply from the inhalant current created by the bivalve.
Other associated fauna include endosymbiont nematodes (Leptosomatum bacillatum, cf. Bongers, 1983), annelids, crustaceans, pycnogonids, echinoderms and fish (Frith, 1976).
Distribution: Northern Atlantic, both along the European coasts and those of America. High arctic occurrence has not been established with certainty, but the species is certainly found in northern Norway, Iceland and northern Canada. Similar sponges occur in the North Pacific but their conspecificity is contested (Erpenbeck et al. 2004). Southward, the species reaches New England and the Mediterranean, although it is uncommon in the Mediterranean itself. Records from the southern ocean (e.g. New Zealand) are doubtful.
Etymology: paniceus (Latin) = of bread, referring to the bread-like texture of dried specimens.
Type specimen information: Original type considered lost; Neotype: BMNH 1964.6.8.6 – Burnham-on-Crouch, Essex; Bowerbank's specimens (Halichondria panicea drawing) are still extant in BMNH. MCS voucher: BELUM Mc109, Portrush, 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 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 difficilis which is purplish and much harder. Halichondria (H.) agglomerans—if a distinct species—has larger oxeas.

Differences between Halichondria (H.) panicea and H. (H.) bowerbanki:H. panicea & H. bowerbanki.
Sources: Vethaak et al., 1981; Ackers et al., 1992 (S.M. Stone, D. Moss, B.E. Picton)

Halichondria panicea