Although familiar to most people as the bath sponge, whose plastic foam imitations ubiquitously adorn the bathrooms of Britain (and probably wherever else you may be), the sponges are in fact a magnificently diverse group of creatures. The great majority would be extremely unpleasant to rub one’s back with, because they have a skeleton; not the soft, protein skeleton with which you are acquainted, but a beautiful skeleton of silica or calcite needles, often microscopic in size but hugely abundant, and very sharp indeed. The skeleton supports a soft body whose basic function is to filter water for organic particles. In general structure, they are approximately vase-shaped, but with enormous variety (for example, many modern species encrust hard surfaces as a thin mat, and others resemble bushes). The body wall is perforated by numerous microscopic canals, called ostia. These canals, with small chambers scattered along them, are lined with peculiar “choanocyte” cells, which possess minute flagellae, or whip-like structures that are waved to create a current though the canals. Water drawn over the cells is also filtered by them, and bacteria-sized particles of organic matter are extracted and absorbed as food. The canals all converge in the central cavity of the sponge, and the water is expelled through the large opening at the top, termed the osculum.
Sponges are in many ways very simple organisms. They have no real nervous system, no digestive system (food is absorbed by the cell that catches it, a process known as phagocytosis), debatably not even any genuine tissues; a broken fragment will grow into an entirely new individual, and sometimes the cells can recombine after being completely disaggregated. However, there is also some evidence that this apparent simplicity is a sham, that they might even have once been relatively close relatives. Their biochemistry includes traces of a complex immune system, and several otherwise unique compounds are shared between sponges and our somewhat surprising cousins, the echinoderms. If so, however, their disguise is sufficiently good that until a few centuries ago, we believed them to be plants; many scientists still consider them as an independent subkingdom, and not true animals at all. It may be some time before their origins are completely resolved, even with the aid of molecular biology.
The evolution of sponges is equally obscure. There are currently three major groups recognised, as well as several minor ones. By far the most abundant today are the demosponges, which possess a siliceous skeleton of uniaxial, triradiate or tetrahedral spicules. Their bodies tend to be extremely complex morphologically, and highly variable; under different conditions, the same species may grow as either an encrusting mat or a branching bush. In many cases, the spicules were fused to create a solid silica skeleton, and these form most of the fossil record. Although some demosponges are known from the Lower Cambrian, in most cases the skeletons were too fragile to fossilise, and they are a very minor component of Palaeozoic faunas.
Also with a siliceous skeleton, but mostly restricted to the deep oceans today, are the hexactinellids. They are named after the skeleton, which is based on a hexactine spicule, a form that has six rays at right angles to each other. There are many variations on these spicules, including four and five-rayed forms, spiny and clubbed spicules, and straight ones with rows of hooks. The body is usually classically vase-shaped, with much less variety than in demosponges. Although most modern species have a regular, three-dimensional mesh of fused hexactines, the earliest fossils are generally unfused, and much more fragile. Often only a single layer of spicules comprised the wall of the sponge, but these could form beautiful -geometrical arrangements. The most characteristic is ‘quadruling’ – a regular grid of crosses where the spaces are subdivided by smaller crosses, and the spaces between those by still smaller crosses…
Both demosponges and hexactinellids possess two types of spicules: megascleres and microscleres. Megascleres are about ten times the size of the latter, which require high magnification in order to find them, a task which is practically impossible in most fossils (only one sponge with microscleres preserved is certainly known from before the Carboniferous, although there are quite a few isolated ones). Microscleres are also extremely varied in shape, and are often quite exquisite. They are, however, essentially absent from the third group, the calcisponges. These also possess calcareous spicules rather than siliceous, which are usually uniaxial or triradiate in shape, and include some species that have the simplest body structure of any sponges. They might be thought to be very widely separated from the other groups, but there is substantial evidence that they were directly ancestral to hexactinellids. An extinct group of calcisponges, the heteractinids, has a skeleton made largely of octactinal spicules (six rays equally spaced in one plane, and two more at right angles), and their arrangement is extremely similar to that of the most primitive hexactinellids. One Burgess Shale genus, Canistrumella, possessed pentaradiate and tetraradiate spicules, derived from the earliest heteractinids by reduction of the number of rays. Eiffelia globosa, another species from the Burgess Shale, contains hexaradiates and hexactines, and provides a convincing example of an intermediate stage. Continuation of this trend would result in triactinal and uniaxial spicules, which are seen in the remainder of the Calcarea. A quadrule-like arrangement composed of triactines is also present in some simple Calcarea.
The sponge fauna of the Llanfawr Quarries is among the most important of its age anywhere. The relatively high diversity is unusual, and combined with superb preservation, has allowed great insights into the barely-known sponges of the Welsh Basin, as well as important details relating to evolution on a global scale. They include an almost perfect intermediate between protosponges and dictyosponges (the two dominant groups of early hexactinellids), the oldest known complete sponge bearing acanthose hexactines, a thick-walled species derived immediately from a protosponge ancestor unlike any previously postulated, and a variety of curiosities. For the sponges alone, this site would be of great international interest. In fact, though, there are also diverse shallow-water sponges preserved at Llandegely Rocks are its lateral equivalents, a unique occurrence with no counterparts known anywhere else. More articulated sponges have been recorded from several other localities as well, making the Builth Inlier one of the most important areas for fossil sponges on the planet.
[5]Acutipuerilis spinosus Botting 2004. Up to 30 mm tall, plus spines.
[5]Asthenospongia cambria Botting 2004. Up to 40 mm diameter.
[2]Brachiospongiid indet. Only specimen is 70 mm tall.
[4?,5]Cyathophycus loydelli Botting 2004. Up to 70 mm diameter, typically ~ 20 mm.
[5]demosponge indet. sp A. Only specimen is 15 mm tall, including basalia.
[2]demosponge indet. sp B. Up to 150-200 mm tall.
[5]Dilatispongia tumidus Botting 2004. Up to 80 mm tall.
[5]Hemidiagoniella caseus Botting 2004. Up to 90 mm tall.
[4?,5]Hemidiagoniella tenax Botting 2004. Up to 150 mm tall.
[5]Heminectere minima Botting 2004. Up to 6 mm tall.
[1,4,5]Heteractinid spicule, perhaps from eiffeliid. Ray length up to ~ 3 mm.
[2]Ordinisabulo quadragintaformis Botting 2005. Up to 30 mm.
[2]Palaeocallyoides improbabilis Botting 2005. Up to 90 mm.
[5]Pirania llanfawrensis Botting 2004. Up to 15 mm tall.
[2]Polycornus entropus Botting 2005. Up to 60 mm.
[2]Polycornua trescelestus Botting 2005. Including crinoid column as central nucleus; up to 120 mm.
[2[Pyritonema scopula Botting 2005. With included crinoid column; up to 200 mm tall.
[5]Solusrectus rosetta Botting 2004. Up to 80 mm.
[2]Stromatoporoid indet. Colony up to 40 mm across; each unit up to 5 mm.
[2]Triactinella rigbyi Botting 2005. Up to 30 mm.
[2]Vadosifistula milvus Botting 2005. Up to ~100 mm tall.
[5]Xylochos palindromica Botting 2004. Up to 12 mm.
To be drawn:
[2]Hindia spheroidalis [Microspongia? sp.; Botting 2005]
[2]indeterminate demosponge (Botting 2005)
[2]indeterminate semi-reticulate demosponge(?)
[5]indeterminate hexactinellid sp. A (Botting 2004)
[5]indeterminate hexactinellid sp. B (Botting 2004)
[5]indeterminate hexactinellid sp. D (Botting 2004)
[2]Microastraeum tenuis Botting 2005
[2]Onerosiconcha gregalia Botting 2005
[4]Pirania?
[2]Pseudolancicula? sp. (Botting 2005).
[2]Pyritonema sp. nov.
[2]Spissiparies
minuta
[4]undescribed demosponge
[4]undescribed hexactinellid
[3,4]undescribed Plectoderma-like
hexactinellid
[5]Conical hexactinellid with stalk.
[5]Undescribed globular hexactinellid.
[4]Undescribed Wapkia-like demosponge.
[4]Undescribed ?anthaspidellid or Multivasculatus-like sponge.
