Morphology of adult Phyllodistomurn umblae (Fabricius) (Platyhelminthes, Gorgoderidae): the effect of preparation, killing and fixation procedures

Twenty two different handling techniques for determining the morphology of Phyllodislormum umblae recovered from the Arctic char, Salvelinus alpinus, in Norway are examined. In some procedurcs both hot and cold fixation were used. Examples of different methods are illustrated by photographs. In addition, the natural morphological variability of P. umblae is demonstrated based on specimens from different hosts and localities in Norway and Sweden. The treatment procedures fall within four main groups: (1) heat fixation, (2) cold fixation, (3) anaesthetization (physical, chemical) and (4) fixation under pressure. It is concluded that only methods which give stretching (and swelling) are passable if acceptable specimen, for measurement and descriptions are to be obtained. This is due to the obscurity of important characters in fluke bodies which are often curled or contracted whcn ‘naturally displayed’ on slides. The acceptable methods for gorgoderid taxonomy based on gross morphology in total mounts are: (1) heat fixation (based on formalin, alcohol and glacial acetic acid), (2) cold fixation (based on glacial acetic acid or Berland's fluid) and (3) anaesthetization (based on heating or freezing in saline or chemical relaxation). The recommended methods are: (1) 10% hot buffered formalin‐saline. if heating facilities are available, or, if not, (2) Berland's fluid.