Worms:
A worm, as you might guess, is technically defined as a long thin thing that generally doesn’t have legs. What you might not guess is that the terms includes about as many different animal phyla (the fundamental, large scale divisions of animal life) as all the rest combined. There are the familiar annelids (including earthworms and bristle worms), the quite well-known nematodes and nematomorphs, and then there’s the rest. Kinorhynchs and acanthocephalans, gastrotrichs and rotifers, sipunculans and echiurans, pogonophorans and trematodes, platyhelminthes and chaetognaths, nemerteans, enteropneusts, phoronids, loriciferans and gnathostomulids, and itsy-bitsy priapulids. All are quite fascinating creatures in their own way, but although some are enormous, many demand a microscope just to acknowledge their presence. ‘Long’ is a relative term.
While I could go into detail about all of them, there’s little point. Their fossil record is appalling in general, and in the case of acanthocephalans and gnathostomulids (‘spiny-headed worms’ and ‘stomach-jaws’), non-existent. The rotifers are known from a single example in Baltic amber, and several other groups (such as enteropneusts) only from rather dubious fossils scattered through the geological past, or just from supposedly characteristic trace fossils (phoronids). Of the rest, though, several have an almost respectable record.
The annelids, for example, include the polychaetes or bristle-worms, well-known to fishermen. Although the worms themselves are soft-bodied, they appear surprisingly often in the Cambrian Burgess Shale-type faunas, forming stunningly beautiful fossils. These are exceptions, but they also possess tiny organic jaws that are surprisingly resistant to decay, which we call scolecodonts, and which can give a surprisingly good indication of their abundance and diversity through time. Although the complete animal is rarely fossilized, it is not impossible to find one in the Builth area, and a couple of possible specimens (albeit without chetae, and difficult to interpret) have turned up already. You need to find a site with effectively exceptional preservation, though, and at that point almost anything can turn up.
Although there is no skeleton, some groups of annelid secrete an external tube, which is independent of the body, but serves as protection; and in some cases, this tube is mineralised. However, a tube is, to be blunt, a tube. Unless we can see the detailed structure, there is little to go on, and other groups of worms (phoronids, for example) also secrete tubes. Although there are some Ordovician tubes that look very like those of modern serpulid annelids, the examples that are known with preserved structure suggest that they are rather different, and belong to some other group of worms entirely. Very little work indeed has been done on Ordovician calcareous worm tubes, and it is probable that those included here are new species, if not genera. They are a rare component of the fauna, and, like many bryozoans, restricted to an encrusting lifestyle. Thus they are found only on the surfaces of other organisms, often specifically related to nautiloids in the youngest beds. One species was apparently attached only to sponges. Any discovery of new specimens of annelids is likely to represent new information, and they should ideally be sent to a specialist. Unfortunately, specialists in Ordovician worm tubes are even rarer than the fossils.
The worms you are most likely to find are palaeoscolecids, a rare group of armoured priapulids. Priapulids are delightful little animals that seem to have been very important in the Cambrian; they have a spiny proboscis that is evertible, and were quite fearsome predators, although now they are a small group of rare, tiny creatures. An offshoot of the large, early forms were the palaeoscolecids. These are protected by an exquisite skeleton of microscopic phosphatic plates (hadimopanellids – see microfossils), embedded in an array of even smaller platelets, which can only be seen with an electron microscope. Three specimens have been found so far at Builth, all from different localities, and they were probably a very widely-distributed and diverse group. Small U-shaped burrows sometimes seen in the top of ash beds might also be attributed to the group, but any such suggestions must be treated with some scepticism, since many other groups could also have made them.
A variety of other worms, including nematodes, can possibly appear given truly exceptional preservation, which Builth is lucky enough to possess. These, however, require specialist techniques and equipment to see, and shouldn’t be expected to be easily visible, even in the extremely unlikely circumstance that you find a rock with one in. In general, complete fossils of worms, despite their unglamorous appearance, are extremely important finds. They tell us that we’re in the presence of extraordinary fossil preservation, and provide information about an ecosystem that is very rarely obtainable indeed. Even the more resilient parts, the tubes and scolecodonts, are well worth keeping. With the appearance of groups like this, you are going far beyond the surface appearance of a fossil fauna, and into the seriously fine details. Exciting stuff.
[5]Chitinozoan animal. Diameter up to ~ 3 mm.
[4]Machaeridian sclerite. These armoured worms possessed an array of volded (V-shaped in cross-section) calcitic plates, and the plates are locally abundant in the Lower Palaeozoic. Because the plates form an array, the shape of individual sclerites can vary significantly in terms of curvature and proportions. Only known from three specimens in Builth However, however, and they're minute. Machaeridians are now thought by most specialists to be primitive molluscs, related to chitons. There are several groups, and this one's a plumulitid. These are only 0.5 mm across, but in general, machaeridian plates tend to be several millimetres.
[2,3,4]Palaeoscolex spp. worm diameter ~ 1 mm, up to ~ 10 mm long.
[2]Palaeoscolex aff. piscatorum Whittard 1953 (Botting 2000, unpublished). Plates ~ 30 μm diameter.
[3]Palaeoscolex sp. A. Plates ~25 μm diameter.
[4]Selkirkia ? sp. The organic tube of a large priapulid worm, well-known from the Burgess Shale. Only one specimen, however, and it's almost entirely encrusted by bryozoans, in contrast to the reconstruction. We thought it was a nautiloid for ages, but it differs in: the blunt, slightly forked narrow end (both ends of the tube were open in life); the complete flattening of the specimen, without fracturing; preservation as a reflective film, rather than a mould; very fine transverse lineations, but not regular enough to be nautiloid growth increments. As far as we know, this is the only one known from above the Cambrian.
[5]Serpulid-like tube sp. A. Approx. 10 mm.
[5]Serpulid-like tube sp. B. Approx. 10 mm.
[1]Scolecodont sp. A. Approx. 0.8 mm.
[5]Wiwaxiid sclerite (?!). If correct, this is really rather important, but one possible sclerite is not enough. Approx. 2 mm.
To be drawn:
[5]Putative nematodes.
[5]Priapulid?
