Nematocyst arrangement on the tentacles of the polyps ofEudendrium(Cnidaria, Hydrozoa)

The nematocyst arrangement on the tentacles of seven Mediterranean species of the genus Eudendrium is described. This character is different in each studied species and therefore may be fruitfully used as a diagnostic tool in this complex genus. The ne‐matocysts of Eudendrium tentacles are always microbasic euryte‐les arranged in more or less tidy bands along the tentacle length. Generally, the proximal portion of the tentacle has a lower amount of capsules or, sometimes, nematocysts are completely lacking in this zone. Differences in nematocyst arrangement are highlighted at three levels: the distribution of capsules along the tentacle; the distribution of capsules in each band; and the orientation of the axis of capsules with respect to the tentacle axis, giving the tentacle surface a smooth or spiny appearance.