Bioclaustration

The star-shaped holes (Catellocaula vallata) in this Upper Ordovician bryozoan represent a soft-bodied organism preserved by bioclaustration in the bryozoan skeleton. (See Palmer and Wilson, 1988)

Bioclaustration is kind of interaction when one organism (usually soft bodied) is embedded in a living substrate (i.e. skeleton of another organism); it means “biologically walled -up”. In case of symbiosis the walling-up is not complete and both organisms stay alive (Palmer and Wilson, 1988).

References

• Palmer, T.J.; Wilson, M.A. (1988). "Parasitism of Ordovician bryozoans and the origin of pseudoborings" (PDF). Palaeontology. 31: 939–949. 
• Cónsole-Gonella, C.; Marquillas, R.A. (2014). "Bioclaustration trace fossils in epeiric shallow marine stromatolites: the Cretaceous-Palaeogene Yacoraite Formation, Northwestern Argentina". Lethaia. 47: 107–119. doi:10.1111/let.12043.