The cnidome of Olindias muelleri (Cnidaria: Hydrozoa: Limnomedusae) from South Adriatic Sea

Olindias muelleri is a hydromedusa distributed in the Mediterranean Sea and tropical Atlantic Ocean. Although this species is frequently reported in the Mediterranean Sea and its sting can cause serious human health problems, no data are currently available on its nematocysts. Therefore, the aim of the present investigation is to provide the description of its cnidome. Three types of nematocysts (microbasic b-mastigophores, pseudostenoteles and microbasic euryteles) and two unidentified types were identified in O. muelleri hydromedusa. For each nematocysts type, the location and abundance were recorded from tentacles, bell margin and manubrium. The three types of nematocysts identified in O. muelleri match with the types observed in the Brazilian Olindias sambaquiensis, the only species of the same genus for which information about the cnidome is available. However, the two species are clearly distinguished in terms of nematocyst size and location. No nematocysts have been observed in the exumbrella and subumbrella of O. muelleri, indicating that only its tentacles, bell margin or manubrium are responsible of envenomation, while the contact with all structures of O. sambaquiensis could be stinging. In addition, the unidentified medium-size capsules represent a character exclusive of O. muelleri.