A new host gorgonian for Bargibanti’s pygmy seahorse from Kochi, Japan

The pygmy seahorse, Hippocampus bargibanti Whitley, 1970 (Osterichthys: Syngnathidae), is an obligate symbiont of gorgonians. The seahorses mimic their host’s colors and shapes and are highly dependent on them. Their hosts are limited to five species of the genus Muricella (Octocorallia: Anthogorgiidae). Symbiosis with other Octocorallia genera has not been reported. However, the host gorgonians are difficult to identify due to limited availability of key taxonomic characteristics. In this study, we describe a pygmy seahorse living symbiotically with a gorgonian in the Kochi Prefecture, Shikoku, Japan. The gorgonian was dissected, morphologically characterized, and identified as a new host species from the genus Anthogorgia (Anthogorgiidae) rather than Muricella, based on differences in sclerite morphology. This is the first study to identify this genus as a host of H. bargibanti. Accurate understanding of host selectivity would be useful in the study of H. bargibanti conservation and ecology.