The brachiopod/bivalve is an internal mould, of a single disarticulated valve. I think this is the explanation for the 'worm things': While it was lying around on the ancient sea floor, its surface was inhabited by serpulid worm(s), leaving their encrusting tunnels. It is those (reversed because of the moulding process) that you see now.
Update, having had a re-think, I think this is more likely:
The brachiopod shell only recently became detached from your specimen. While it was still attached, the borings were made, initially in the shell, but penetrating into the sediment filling it. Since the shell came loose, leaving you with the cast, you see just parts of the borings.
These sorts of borings are generally attributed to small snails, sponges, or polychaete worms
http://en.wikipedia.org/wiki/PolychaeteThis is a pertinent paper on polychaete (annelid) worms and their borings - http://www.jstor.org/discover/10.2307/3881669?uid=3737848&uid=2&uid=4&sid=21102735659821 (read the abstract at the end).
Some refs re serpulid worms:
- http://paleo.cc/ce/tracefos.htm (search for 'Serpulid')
Scaphopod - yes.
The little white thing is an internal mouldof a bivalve.
Thanks for the reply. In the part you reacently added, did you say it was worms that made those burrowings? If it was worms, did they make those burrowings before or after fossilisation?
These worms could make borings pre- or post fossilization, but pre-fossilization is more likely, not least because of the environment - which would still be marine. They can make borings in still-living bivalves and brachiopods, but basically it is the substrate they are interested in, alive or dead. The test (shell) of a dead bivalve or brachiopod, lying on the sea bed, could quite easily become bored by these polychaete worms. In siuch situations, the borings could extend into the sediment the test is resting on. Such sediment can be loose, which would not allow good preservation of borings, or indurated (hardened by the onset of cementation), which would.
Hi again mike,
Here Is a close-up picture of the worm things. Can you be sure they are worm burrowings? I am going to the same place next year so hopefully I can find some more.