A new hexactinellid sponge from the Silurian of the Pentland Hills (Scotland) with similarities to extant rossellids

The Pentland Hills sponge fauna (Llandovery, Telychian) consists of an unusual, aberrant assemblage, but of low diversity. A new specimen of a unique sponge, Eoghanospongia carlinslowpensis gen. et sp. nov., is described from the classic locality of R82. The mushroom-shaped, probably stalked body (peduncle attachment to body not exposed) resembles that of some living rossellids, especially Caulophacus. The sponge also shows prominent projecting pentactins and monaxon derivatives - a spicule type diagnostic of the Rossellidae among living taxa, albeit in a robust form not described from extant sponges, including Caulophacus or other pedunculate lyssacinosidans. Certain attribution to the Rossellidae is not possible from the single specimen, largely because of weak preservation of the primary spicule skeleton, but no other fossil or modern sponges show any significant similarity to it. Although similarly early relatives of the Rossellidae have recently been described from elsewhere, the new sponge is even more unexpected in being from a shallow-water environment, making the absence of rossellids through the rest of the Palaeozoic much more problematic.