What happened to this belemnite ?

[Brevicollis]

I was just searching for interesting belemnites in my belemnite jars, and found this one with an interesting white mark on, and in it. 
What caused it ? Is an infilled scavenging trace of a worm, maybe some sponge roots, or a pathology ?
 

I found it in Denmark, probably Hejsager Strand.

Its 1,4 cm long, and from the maastrichtian era, around 65-70 million years old.