A possible response to light of larvae of Black Sea ctenophore Mnemiopsis leidyi of two age groups (first to fourth day and one-two weeks after hatching) was experimentally studied. The larvae were placed in a Petri dish with seawater, in which two areas (light and dark) were created using a light source and a black opaque background. The number of larvae in each area was recorded for an hour after the start of the experiment. It was found that on average 77 % of the early stage larvae (first to fourth day) migrated to the dark area after an hour. We hypothesized that Mnemiopsis leidyi early stage larvae have negative phototaxis. Similar response of the older larvae (one-two weeks) was not recorded.
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