ABSTRACT
Leptometra phalangium and its myzostomid symbiotes were collected off Banyuls-sur-mer in February 1991. Out of the 204 L. phalangium observed, 33 (16 %) were infested by Myzostoma alatum (1 to 6 myzostomids per host) and 31 (15 %) were infested by Pulvinomyzostomum pulvinar (1 to 2 myzostomids per host). Coinfestation was observed in 2 cases (1 %). Larval, metamorphic and postmetamorphic developments of M. alatum as well as its reproductive process have been observed. Pelagic larvae of M. alatum develop in metatrochophorae which begin their metamorphosis when they are 7-days old. Two ectosymbiotic postmetamorphic stages have been recognized in M. alatum: a male stage (individuals from 0.4 to 1 mm long) and a hermaphroditic stage (individuals from 1 to 2.4 mm long). Hermaphrodites and largest males attached to the tegmen of the host’s integument while small males attached to the antero-dorsal part of the hemaphrodites. Two endosymbiotic postmetamorphic stages have been recognized in P. pulvinar: a juvenile stage (individuals from 0.6 to 1 mm long) and a female stage (individuals from 3 to 4 mm long). Females totally filled the host’ stomach while juveniles loosely attached to either the females (small juveniles) or the host’s digestive wall (largest juveniles). Both M. alatum and P. pulvinar ao not cause injuries nor provoke particular reaction of their host (they only divert alimentary particles caught by the comatulids). Each symbiosis could be considered more a commensalism than a parasitism.
