Genus Eirene Eschscholtz, 1829

Diagnosis: Eirenidae medusa with distinct, broad gastric peduncle; cirri absent; with or without excretory pores; 4-6 simple radial canals; gonads on subumbrellar part of radial canals, not extending to gastric peduncle; numerous statocysts (>8).

The hydroids of ‘ Campanulina ’, ‘ Campanopsis ’ or ‘ Eugymnanthea ’ type (see Bouillon et al., 2006).

Remark: Clytia species with a short gastric peduncle like Clytia gregaria (see below) are formally not distinguishable from Eirene species. Thus, some nominal Eirene species (Schuchert, 2017a; see Du et al., 2010 for a key to the species) with a shallow peduncle and no excretory papillae could therefore also be Clytia species. Life-cycle studies or DNA barcodes (Schuchert et al., 2017) have to confirm the identity of Eirene pentanemalis Lin, Xu & Huang, 2013, Eirene brevistylus Huang & Xu, 1994, and other similar species.