A UCD researcher is using DNA finger- printing to study the 400 million-year-old sea-slug family as a way to construct a family tree, writes Claire O'Connell.
Some designs were built to last. Especially in the case of primitive chitons, deep-sea molluscs whose body format has changed little for tens of millions of years.
But a researcher at University College Dublin (UCD) has gone beyond the superficial and discovered that "living fossil" chiton species have remarkable variations in their DNA. This could help refine their family tree and make it easier to identify them in the wild.
The fossil record shows that chitons, the most basic type of mollusc, have been around for at least 400 million years, explains museum collections researcher Julia Sigwart, who is based at UCD's school of biology and environmental science.
Over that period, chitons tried out several body types but ran into various dead ends: "There are lots of weird and wonderful creatures that used to be crawling around the bottom of the sea that are no more," says Sigwart.
Then, about 60 million years ago, a group called the "leptochitons" turned up in the fossil record. They appear to have hit on a recipe that works, because their body format looks the same in living creatures today.
However, the roughly 120 known species of leptochiton, are currently classified "in the same pot", making it difficult for researchers to identify them if they are discovered, according to Sigwart.
So she is looking beyond the outer similarities to see if their genetic makeup can help refine the family tree. This would make their identification easier in the field and, on a larger scale, help unveil their relationships with the rest of the world's molluscs.
To do this, she is peering into their DNA. "I see using molecular sequences as yet another set of characters for telling animals apart," she explains. "And I want to know if species in this group are actually all related to each other. They probably are, but I want some reassurance."
However, getting material from the animals to work with is not that easy, because they live a kilometre under the ocean's surface. "These things come from the deep, deep sea, and they are quite rare on an ecosystem level. So they are incredibly hard to get hold of," says Sigwart.
"It would be economically impractical for me to hire a boat and go out into the middle of the ocean and try and get one. So I collaborate with museums and universities that run deep-sea expeditions. They know that I like chitons so when they catch one, they set it aside for me."
Another challenge is that the animal tissue can be traumatised when it is hauled from the ocean depths to sea-level, making analysis more difficult. But when Sigwart gets hold of usable chiton tissue, she works with Prof Gonzalo Giribet at Harvard University to extract and analyse the animal's DNA.
In the 75 species examined so far, she has found that even though leptochitons look similar to each other on the outside, key DNA sequences show substantial differences from one species to the next.
And as the new DNA map of these creatures emerges, Sigwart hopes to identify related sub-groups of leptochitons and zone in on quick ways for biodiversity researchers to distinguish them visually, particularly in the South Pacific, where the molluscs seem to be unusually abundant.
"If I can find out more about how many of these species are real species, or how many of them look different but are actually the same species, that can help me identify the useful characters in their anatomy. Then I can tell other people, 'when you haul up a bucket of those you want to count the spines on the left side because that works'," she says.