Parasitism on graptoloid graptolites

A review of evidence for parasitism on graptoloid graptolites is presented. The phenomenon is rare. having been recorded in only a few biserial forms and straight monograptids. Most periderm outgrowths secreted as a response to parasitism an small and blister-like, but in two new specimens remarkabl e tubular outgrowths occur. These would have had a detrimental, but clearly not fatal, influence on the functioning of these graptolites. particularly with regard to the hydrodynamics and buoyancy of the rhabdosome and the en ergy expended in secreting additional periderm.