The ocean-dwelling creatures are so unusual that an entire new taxonomic family was created to classify them, scientists report today (Sept. 3) in the journal PLOS ONE. Yet nothing is known about their lifestyle, their feeding habits, how they reproduce or if they float or attach to the seafloor.
“We don’t even know if they’re upside down,” said lead study author Jean Just, a taxonomist at the Natural History Museum of Denmark.
The two new species described in the study were officially named Dendrogramma enigmatica and Dendrogramma discoides. Their tops are flat discs about 0.5 inches (about 1 centimeter) wide. Inside the discs, a fan of digestive tubes delivers nutrients, radiating outward like bicycle tire spokes. The center “mouth” opens into the stalk, and is probably for both eating food and excreting waste, Just said. (Many primitive species have this single gut.) Of the two new species, one has a shorter stalk and smaller disc compared with the other, though the difference is only a few millimeters.
Only 18 Dendrogramma specimens exist; they were all caught in 1988 on a research ship exploring the eastern Bass Strait between Australia and Tasmania. The weird creatures were found in a mix of seawater and sediment scooped from 3,280 feet (1,000 meters) below the ocean surface.
After returning to shore, scientists sifted through the marine life collected during the research cruise. Just, who was then at Australia’s Museum Victoria in Melbourne, said he recognized the creatures were strange and special, but thought they were a new kind of jellyfish.
However, a closer look revealed no stinging cells, the hallmark of true jellyfish. No tentacles dangle from the Dendrogramma, and their tiny, hairless bodies also lack the swimming cilia that define comb jellies, another type of translucent ocean blob.