A Sea Creature That Blew Scientists’ Minds
By LIDA TUNESI
An unsuspecting citizen of the ocean that’s been around for over 500 million years has broken the record for the longest mitochondrial genome found in an animal. The creature is a colorful tube anemone.
One of the species studied, Isarachnanthus nocturnus, has a mitogenome of 80,923 base pairs of nucleobases, the fundamental unit of the DNA double helix. That’s 4.9 times longer than the mitogenome of humans. The other species, Pachycerianthus magnus, is a close second with 77,828 base pairs.
The researchers, including Professor Mercer Brugler (New York City College of Technology), published their results in Scientific Reports. Lead author was Sergio Stampar, Universidade Estadual Paulista, Brazil, whose beautiful photographs illustrated the study.
Both species, also known as ceriantharia, have tube-like bodies that can measure around 2 feet long, and two sets of tentacles for eating and defense. They look like sea anemones, though they’re different.
In studying the two species, researchers came across another surprise: Their mitochondrial genomes are linear, rather than circular. Both discoveries could help scientists figure out how best to classify the creatures in the animal kingdom.
DNA is usually thought of as being stored in the nucleus of a cell. But many organisms also have DNA in their mitochondria, an organelle responsible for making the cell’s chemical energy. In most multicellular organisms, humans included, this “mitogenome” is shaped in a circle. In fact, the mitogenome is circular in all other anthozoa—the parent category that includes tube anemones, making the discovery especially surprising.
“It blew our minds,” said Brugler in an interview with the American Museum of Natural History. “Now that we understand the architecture of their mitogenome, we can quickly sequence and assemble additional mitogenomes from a diversity of tube anemone species and finally nail down where this group belongs in the cnidarian tree of life.”
Tube anemones and other anthozoa fall under the cnidaria category, which also includes corals and jellyfish. But scientists have been hard-pressed to figure out exactly where anemones fit, debating their relationships to other animals based on anatomy, features of their larval state, and their DNA. They were once grouped together with black corals but have since been separated into their own subclass. The researchers hope this discovery is a step toward finalizing the anemones’ placement.