Curious growth pattern or parasitism?

[Kane]

I have been finding a number of Terataspis parts in the last week among glacial erratics near my home, but I encountered something that is anomalous (to me). 

 

Collected here is the ventral shell and the dorsal steinkern of a Terataspis glabella, a little over 2" (5 cm) on its widest end. Within the furrow area, there are these concentric rings. Perhaps I don't pay enough attention to the ventral side's microsculpture / ornament, and possibly the explanation is face-palm simple, but I was still curious as to what can explain this form of growth process. I did not see anything specific in the Treatise about this feature. Is there perhaps a modern analogy among arthropods that have this sort of concentric ring growth on the ventral side of the shell? I am sure I will feel quite silly if these rings turn out to simply be some kind of parasitic activity. 

 

That being said, there is a paper I need to track down on trilobites playing host to parasites. 

 

Pictured here would be the ventral (with the rings on the furrow), and two images of the dorsal side (steinkern) where the rings can be seen in the shadow of the glabella in the second image. 

[Kane]

(I suppose a better, straight-on image in better lighting would be much more helpful!)

[piranha]

Beekite rings?

 

[Kane]

1 minute ago, piranha said:

Beekite rings?

 

I think you have it! I am satisfied with that as a solution! (My thanks, of course  ). 

 

As good a time as any to link to one of your posts where beekite rings have appeared on a trilobite: 

 

[FossilNerd]

Beekite was my first thought as well.