Abstract.  For well over a century, organisms have been documented as attached to or bored into
  shells of externally shelled cephalopods.  These organisms range in age from the Ordovician to the
  present and include algae, fungi, foraminiferans, poriferans, inarticulate brachiopods, bryozoans,
  lepadomorph cirriped crustaceans, serpulid worms, gastropods (including limpets), and pelecypods
  (including oysters), as well as entities of uncertain biologic affinities.  Usage of the terms epizoa,
  epibiont, epifauna, and related words has been less than consistent.  An "epizoon" is an animal
  that spends its life attached to or otherwise inhabiting the exterior of another living animal.  The
  term "epicole" is proposed as the appropriate term to denote an organism that spends its life
  attached to or otherwise inhabiting the exterior of any more-or-less hard object, be it living, once li-
  ving but now dead, or inorganic, and on the sea floor or not. lt commonly is problematic as to whe-
  ther epicoles present on cephalopod shells were epizoa (i.e., were present while the cephalopod
  was alive).  Evidence for a living association includes the orientation of the putative epizoa and
  their location on the cephalopod conch, whether they were overgrown during the ontogeny of the
  cephalopod, and, sometimes, the known (or inferred) environmental needs and ways-of-life not
  only of the taxa of potentiell epizoa but also of the cephalopods.  The possibility of organisms living
  a "necroplanktonic" existence on dead but still-floating ammonoid shells provides interesting but
  commonly unresolvable interpretive challenges.  Organisms attached to cephalopod shells are gene-
  rally uncommon.  This paucity may be due to any of a number of the following: constructional features
  of the cephalopod conchs, the presence of an anti-fouling organic layer (like the thick periostracum
  of Nautilus scrobiculatus), chemical-defense mechanisms, behavioral factors (such es deliberate
  cleaning of the conch by the cephalopod), environmental factors controlling the epicoles, evolution
  of organisms with the potential to become epicoles at certain times in the geological record, tapho-
  nomic destruction, and, perhaps, a failure of some cephalopod workers to observe and report epi-
  coles.  Although this report does provide some new examples of epicoles on cophalopod shells, at
  present, there are too few data available to provide reliable overall conclusions as to distribution
  and evolution of epizoism on cephalopods through geologic time and ecologic space.