Discovery of Cladonema multiramosum sp. nov. (Cnidaria: Hydrozoa: Cladonematidae) using DNA barcoding and life cycle analyses

In contrast to typical planktonic hydromedusae, Cladonema medusae are mostly benthic, with specialised adhesive branches to adhere to the substrate. In this study, a Cladonema species discovered in a laboratory aquarium in Fuzhou, China, was confirmed as a new species, based on morphological and molecular analyses. The species was named Cladonema multiramosum sp. nov. Its medusa is distinct from that of congeners possessing substantially more adhesive branches (8-24, rarely 5-7), and tiny branches on the upper radial canals. The validity of C. multiramosumum sp. nov. was also supported by molecular phylogenetic analyses based on the mitochondrial 16S rDNA sequence. However, C. multiramosum sp. nov. medusa also displayed considerable phenotypic plasticity with respect to its radial canals, tentacles, stinging branches per tentacle, oral tentacles, manubrium, and gonads, hindering species identification based solely on morphology. Although some morphological characteristics of hydroids (filiform tentacles and medusa buds) and nematocysts could also be used as diagnostic characters in the genus Cladonema, this information is unavailable for some Cladonema species. Thus, the taxonomy within the genus Cladonema was re-evaluated based mainly on the morphological characteristics of the medusa. Further revision of the genus Cladonema should be made when supplementary information on the life cycle and DNA barcoding are updated.

Automated summary

This study confirms a new species of Cladonema, named Cladonema multiramosum sp. nov., discovered in a laboratory aquarium in Fuzhou, China, through morphological and molecular analyses. The distinctive features of the Cladonema multiramosum sp. nov. medusa differentiate it from other congeners, although the species also exhibits significant phenotypic plasticity, hindering species identification solely based on morphology. Therefore, a re-evaluation of the taxonomy within the genus Cladonema is necessary, with further revision expected based on additional information on the life cycle and DNA barcoding.