Cnidaria:
This is a very simple group of animals, and are believed to represent, along with sponges, some of the earliest-evolved groups of multicellular animals, or ‘metazoans.’ They will be familiar to all as corals, sea anemones and jellyfish, but include the slightly more obscure hydroids and gorgonians as well. Some of these, you might think, should have a good fossil record – and in the case of corals, you’d be right. The problem is, this record doesn’t really start until the Mid to Late Ordovician, and there aren’t any yet described from Builth. Of the others, the jellyfish and anemones are really rather shy as fossils, being composed not merely of soft tissue, but of really soft tissue. Unsurprisingly, jelly doesn’t fossilize well. In fact, hardly ever.
The record of cnidarians in the Builth Inlier is therefore rather scant. We do actually have a fairly convincing coral-like thing that we’re working on, but other than that, it’s just a scattering of hydroids. You are probably familiar with these, but just don’t realise it. They tend to be abundant in rockpools, forming brittle, thin-branched seaweed-like structures made of a chitin-like substance. Most of them are colonial, with each branch having lots of little pores from which tiny anemone-like polyps (zooids) emerge. The skeleton is not mineralised, in general, but is still quite resistant to decay, in the same way as graptolites. It is usually difficult to distinguish them from graptolites, in fact – usually, they’re described by graptolite specialists, since these are the people that can recognise what they’re not, and therefore identify them as what is really the only other possibility.
The other group that turns up quite commonly is an extinct one, consisting of the sphenothallids and colulariids. These had broadly tubular to conical shells made of phosphate, and range from minute (only millimetres long: Sphenothallus) to quite large (conulariids can be up to 30 cm). The diagnostic feature is four-fold or eight-fold symmetry, and a phosphatic skeleton (if it’s preserved). Sphenothallus has not been described from Builth, although we have some specimens we collected ourselves, but conulariids have been widely reported – although most of the specimens I thought I’d found turned out to be crushed nautiloid shells instead. A few genuine ones have turned up recently, though.
[3]Conularia? sp., estimated approx. 20 mm diameter.
[1]Hydroid indet. sp. A. Colony ~ 20 mm.
[3]Hydroid indet. sp. B. Colony ~ 5 mm? Perhaps much larger.
[4]Sphenothallus sp. Fragment shown is ~ 5 mm long.
To be drawn:
[2]solitary coral-like structure, 5 mm diameter.
[4]Conularia coronata sp. B, approx. 40 mm diameter.
[1]Conularia? sp.; single pair of specimens, reported by Brian Beveridge (see Images/photos/Gilwern)
[5]Solitary hydrozoan.
