New jellyfish species with cross-shaped stomachs discovered in Japan

A study from a team of researchers from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has unveiled a new jellyfish species, Santjordia pagesi.

This finding marks the emergence of a novel genus and species within a previously unknown subfamily dubbed the Santjordiinae.

Santjordia pagesi, like other jellyfish, is see-through, but its bright red stomach serves a special purpose. It helps hide bioluminescent creatures swallowed by the jellyfish from predators.

According to researchers, bioluminescence, where living things emit light, is a common occurrence in the deep, dark sea. 

The team's work sheds light on the complex biodiversity of marine life. The Institute for Extra-cutting-edge Science and Technology Avant-garde Research at JAMSTEC spearheaded this venture.

The team claims that Santjordia pagesi's emergence serves as a testament to the vast mysteries waiting to be uncovered beneath the waves.

The details of the team's research were published in the journal Zootaxa.

Extensive work

The team at JAMSTEC, aiming to develop sustainable seafloor mineral resource utilization, has conducted surveys in various calderas in the Japan region, focusing on ecosystems in submarine calderas suitable for resource extraction.

The Sumisu Caldera (Smith Caldera) stands out, situated around 296 miles (460 kilometers) south of Tokyo. Its 6.2 miles (10 kilometers) diameter and depth exceeding 1,000 meters create a closed environment conducive to mining activities.

In 2002, using the ROV Hyper-Dolphin, researchers stumbled upon a peculiar jellyfish inside Sumisu Caldera. Morphological analysis hinted at a new species, though only one specimen was collected.

Delays in species description are common due to potential deformities or mutations. However, a 2020 expedition employing the unmanned KM-ROV provided a breakthrough.

According to the team, another specimen of the same jellyfish species was observed and collected, affirming its novelty. 

André Morandini, co-author of the study and a professor of zoology and director of the Center for Marine Biology at the University of São Paulo’s Institute of Biosciences in a statement said:

“The species is very different from all the deep-sea medusae discovered to date. It’s relatively small, whereas others in this kind of environment are much larger. The bright red coloring of its stomach probably has to do with capturing food.”

Novel genus

Genetic analysis of the specimen, with no closely related matches in GenBank, prompted the research team to gather and analyze jellyfish species worldwide.

The study identified Tiburonia granrojo, Deepstaria enigmatica, and Stygiomedusa gigantea as the closest relatives, characterized by bell-shaped bodies lacking tentacles but with oral arms.

The newly discovered jellyfish, while also lacking marginal tentacles, features sub-umbrella tentacles—an uncommon trait among its relatives, according to researchers. 

While unable to pinpoint the exact closest relative based solely on genetic analysis, it's determined that the new species belongs to the family Ulmaridae. However, taxonomic reconsideration suggests dividing Ulmaridae into multiple subfamilies.

Despite the need for further genetic sampling, the classification of this jellyfish as a new species, genus, and subfamily remains significant. Through this study, the team highlights the complexity of marine taxonomy and underscores the necessity for continued exploration and research.

Santjordia pagesi's distinctive feature—a bright red stomach that forms a cross when viewed from above, is reminiscent of St. George's cross.

Its Latin genus name, Santjordia, pays homage to this striking characteristic, while its Japanese counterpart is Sekijuujikurage-zoku. The species epithet, pagesi, honors Francesc Pages, a respected jellyfish taxonomist from Barcelona. 

Despite extensive marine surveys, Santjordia pagesi has been found exclusively within known submarine hydrothermal deposits in the Sumisu Caldera, rendering it rare.

While it's presumed that a polyp generation is attached to the seafloor, these polyps might be confined to specific, unique rocks in the exposed seafloor resources.

According to the team, this rarity suggests that Santjordia pagesi could offer valuable insights into assessing the environmental impact. 

Study Abstract:

An undescribed species of ulmarid medusa was observed in situ and captured at 812 m depth within the Sumisu Caldera, Ogasawara Islands, Japan. Morphological and molecular evidence points to it being distinct from other ulmarid medusae and a new species (pagesi), genus (Santjordia) and subfamily (Santjordiinae) are herein erected to contain it. This new subfamily of semaeostome ulmarid medusae has both marginal and subumbrellar rhopalia, making it unique within the order Semaeostomeae. Although the combination of subumbrellar tentacles and the lack of branched canals should warrant the erection of a new family within the Semaeostomeae, a lack of information on the gonad structure and poor bootstrap support in the molecular phylogenetic tree cause us to relegate it to the catch-all family Ulmaridae, until greater taxon sampling and phylogenetic analyses are carried out for the Semaeostomeae.

Originally published on Interesting Engineering : Original article

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