Early stage radiolarian colony OR arrow head worm?
My guess was arrow head, but is there a way to tell the difference?
Definitely not an arrow worm and it doesn't have any visible features of Radiolarian colonies either (no visible Radiolarian blobs, no halo around, moreover, it is very think for one). I'm not sure what it really is but I'd say it is just a debris, looks like a tentacle which has been divorced from a jellyfish.... I would ignore that in the classification completely.