Wow! Agreed. Looks like the barnacle picked the wrong substrate and got overgrown on the next whorl. Looks like some Caulostrepsis borings on the barnacle as well!

Lots of modern encrusters seem to prefer cryptic settlement and concave surfaces, but not barnacles. Curious about that.

#Terebralia palustris with a ton of post mortem #polydorid borings
#polydora
#caulostrepsis
#neoichnology
#molluscsofsrilanka

So many good ones already called out by name, so I'll pick something different: the boring, kleptoparasitic Polydora, which produces the trace fossil Caulostrepsis. As the host grows, they maintain their position at the edge of the shell so as to take advantage of its inhalent current for feeding.

You would think that older shells, being exposed for a longer time, might accumulate more sclerobionts, but that doesn't seem to be the case. Some taxa colonize live hosts, like Polydora: a boring kleptoparasitic worm. Postmortem colonization may select for microbial biofilms associated with decay.