Aeolidiella alderi

Aeolidiella alderi is a small nudibranch that can grow up to 37 mm in length. It has a flattened and broad body, distinguished by a pair of oral tentacles that are longer than its rhinophores. The dorsal surface features up to 16 oblique rows of cerata, which are extensions of the body wall that aid in respiration and vary in color based on the nudibranch's diet. The first row of cerata is white and forms a collar around the body. This species is found in the intertidal zone of northwestern Europe, particularly under boulders and in rock pools, and is recorded at various dive sites across the North Atlantic and Mediterranean seas. As a carnivore, Aeolidiella alderi primarily feeds on sea anemones, showing a preference for species like Cereus pedunculatus and Diadumene cincta. It approaches its prey cautiously, using its cerata to deliver stinging cells from the anemones, allowing it to consume them safely. Reproduction occurs year-round, as this species is hermaphroditic, laying large eggs in spiral strings on the substrate. The young hatch directly into a crawling form, developing cerata as they grow. Diving encounters with Aeolidiella alderi may involve spotting this nudibranch in its natural habitat, where it can be observed moving slowly and cautiously among rocks and anemones. Its unique body structure and feeding behavior make it an interesting subject for underwater observation and photography.