Hello Hydromedusa of the Marianas

Don’t be jelly of this incredible set of observations of abyssal plain hydrozoans!

While you might be tempted to call all clear, pelagic, drifting predators “jellyfish”, did you know this oversimplifies a massive group of cnidarian creatures? Check out this highlight compilation of many beautiful hydrozoans found on a dive along the abyssal plain east of the Mariana Trench.  

Hydromedusae are generally smaller and more delicate than true jellyfish (Scyphomedusae), and feed by trailing stinging tentacles through the water as they drift in the darkness. Experts onboard and onshore identified at least one of the sightings as from the benthopelagic genus Ptychogastria. Look closely at the bell too; many hydromedusae lack lobes along the umbrella edge, giving a very smooth appearance. This exploration dive brought ROVs Little Hercules and Atalanta to the seafloor in a never-before-surveyed region of the seafloor, 155 nautical miles east of Tinian Island in the Commonwealth of the Northern Mariana Islands. The expedition goals were to characterize the deep ocean’s habitats, biodiversity, bathymetry, and geological formations, providing high-quality, publicly accessible data about the deep sea. 

Ocean Exploration Trust's Deep-Sea Habitats in the Mariana Islands I & II (NA179 & NA180) expeditions are primarily supported by NOAA Ocean Exploration via the Ocean Exploration Cooperative Institute, with additional support from the Bureau of Ocean Energy Management for AUV Sentry’s participation.