Morphological and Molecular Analyses of Cladonema cf. Californicum (Hydrozoa: Anthoathecata) from China

In this study, hydrozoan medusae collected from a home aquarium in Sanming, China, were tentatively identified as <i>Cladonema</i> cf. <i>californicum</i> Hyman, 1947, based on DNA barcoding. Morphologically, these specimens differed from known <i>Cladonema</i> medusae, including <i>C. californicum</i>, by possessing a manubrium with protuberances and tentacles with one to three (typically two) adhesive branches, along with three to six (usually four) stinging branches emerging laterally from the main tentacle shaft. These morphological distinctions were supported by molecular phylogenetic analyses using the mitochondrial 16S rRNA and cytochrome <i>c</i> oxidase subunit I (COI) gene sequences. Nonetheless, COI sequences revealed that <i>C.</i> cf. <i>californicum</i> clustered with juvenile <i>Cladonema californicum</i> medusae from California, USA, with a minimal genetic distance of 0.008, indicating potential conspecificity. Given the morphological similarities among juvenile <i>Cladonema</i> medusae, the Californian specimens may have been misidentified. Further investigations focusing on the polyp stage and geographic distribution are necessary to fully resolve the taxonomic status of these medusae and clarify their relationship with <i>C. californicum</i>.