mesonia hippocampi mesonia hippocampi mesonia hippocampi is a gram-negative and rod-shaped bacterium from the genus of mesonia which has been isolated from the brood pouch of an ill seahorse (hippocampus barbouri). mesonia hippocampi scientific classification domain: bacteria phylum: bacteroidota class: flavobacteriia order: flavobacteriales family: flavobacteriaceae genus: mesonia species: m. hippocampi binomial name mesonia hippocampikolberg et al. 2015 type strain 96_hippo_ts_3/13