Welcome to the Subfamily
Almost from the moment George Matsumoto of the Monterey Bay Aquarium Research Institute first saw “Big Red,” he knew he was looking at a new species of jellyfish. It looked just plain bizarre: bulbous, dusky red, and huge, nearly one meter (about three feet) in diameter, with several fleshy arms instead of tentacles, like a balloon with greedy fingers. When Matsumoto and his coauthors, Kevin Raskoff of California State University and Dhugal Lindsay of the Japan Marine Science and Technology Center, described it in a scientific paper in 2003, they gave it a more official name: Tiburonia granrojo.
“Because we’ve spent so much time in the field and we’ve seen so many pictures, whenever we see something that doesn’t match up we get this feeling that it’s a new species,” Matsumoto says, “which of course generates a lot of excitement and enthusiasm.”
These are busy times for jelly discoverers. The use of submersible vehicles has enabled scientists to explore the world of jellies in depth; new creatures are constantly appearing. In February 2004, Raskoff and Matsumoto announced the discovery of yet another deep-sea jelly, Stellamedusa ventana, a tentacleless organism they’ve affectionately named “Bumpy” for the many warty lumps on its softball-size body.
The best-known groups of jellies are the jellyfish and comb jellies. Jellyfish belong to the class Scyphozoa within the larger phylum Cnidaria. All cnidarians possess stinging cells called nematocysts. The phylum Cnidaria also include the classes Hydrozoa, Anthozoa (corals and sea anemones), and Cubozoa (sea wasps and box jellies). Comb jellies belong to an entirely separate phylum, Ctenophora. The ctenophores gather food and ensnare prey with sticky cells rather than stinging cells. Unlike cnidarians, which propel themselves with rhythmic contractions of their bells, comb jellies paddle through the water with tiny oarlike cilia on the outsides of their bodies. Though many jellyfish and comb jellies look outwardly similar, the two groups are evolutionarily distinct. Only recently have scientists successfully described Cnidaria and Ctenophora as distinct phyla. Due to similarities in appearance, the two together had previously been known as coelenterates.
Classifying a new jelly species is a difficult process. “Every time I do it, it’s a lot of work, but it’s also very rewarding,” Matsumoto says. A scientist must have a good understanding of what has already been described, and must do a very thorough review of the existing literature in order to feel confident that the “new” species is in fact new to science and not just new to the scientist. “As with anything, you can’t know what’s new until you’ve spent some time looking at what’s already out there,” Raskoff says.
“Big Red” was first spotted on video during a submersible dive in 1993. In 1998, after several more sightings, Matsumoto was called in to identify it. He and Raskoff went back and pored over years of video footage to learn more about the animal’s typical size and geographic range. They also closely examined its anatomy for comparison with other known species. Big Red is unusual in that, unlike most jellyfish, it has no tentacles, only several fleshy arms to capture food. It is so different from other jellies that researchers ultimately assigned it to its own subfamily, Tiburoniinae.
Traditionally, biologists distinguished and classified jellies strictly according to physical shape: the number of tentacles, or a certain shape of the stomach. But this approach can be misleading, especially with jellies. “They can be very close cousins and look very different,” Raskoff says. “And things that look very, very similar can actually be very far apart, evolutionarily speaking.” It was years before scientists realized that polyps, small organisms that grow on surfaces such as rocks, are actually the immature form of free-swimming jellies. Matsumoto and Raskoff found that the number of arms on Big Red--often a reliable guide for distinguishing a species--varies anywhere from four to seven, depending on the individual.
The advance of molecular biology has greatly aided scientists in their ability to identify and classify organisms. Ultimately, the taxonomy of organisms--how they are grouped in relation to one another--should reflect a common evolutionary ancestry. By examining and comparing DNA, which organisms inherit through reproduction, taxonomists have gained a much clearer picture of how organisms are related to one another across all taxonomic levels.
Recently, Raskoff and another MBARI scientist, Steve Haddock, have been taking a close look at the order Narcomedusae (phylum Cnidaria), a group of jellies that outwardly look very similar to one another. Based on physical appearance, scientists had previously declared certain Narcomedusae to be more closely related than others. But, says Raskoff, “the genetic evidence supports a very, very different linkage between these different groups. We found that the traditional taxonomy that has been accepted for hundreds of years for a large order of jellies turns out to basically be completely false.”
Through genetic analysis, biologists are slowly gaining a better understanding of how and when the jellies evolved. Needless to say, fossils of jellies are few and far between. The evidence now suggests that jellies are an ancient life-form, hundreds of millions of years old, and probably predate most of the more familiar, complex animals. But many questions remain. For example, the comb jellies are typically classified into two types, those with tentacles and those without. Which type is older? Did the tentacleless kind appear first and the tentacled kind evolve later? Or did tentacles come first and then, in some comb jellies, disappear over time? Only further study and exploration will tell. What marine researchers know for certain is that the jellies they’ve discovered so far represent only a small fraction of what’s out there.
“We’ve been doing this for 15 years now, and yet we still see new stuff almost every dive,” says MBARI scientist Bruce Robison. “And that’s just in Monterey Bay. Our knowledge about the deep sea is still so poor that even after all these years of diving in this one spot, we still see new things all the time.”
Meanwhile, Matsumoto and Raskoff do their best to keep up. In addition to the several new jellies they’ve discovered in the past couple of years, they have perhaps ten more that look like solid candidates for new species. They’ll officially describe them, Raskoff says, just as soon as they discover something else: some spare time.
Classification of Gelatinous Zooplankton
MBARI News and Information
Tree of Life Web Project
Where do jellies fit in?
More About This Resource...
Supplement a study of biology with a classroom activity drawn from this Science Bulletin essay.
- Have students read the essay (either online or a printed copy).
- Working individually or in small groups, have them visit The Jellies Zone website to learn more about the classification of gelatinous zooplankton.