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Home - Global Worming – Summer 2010

While marine worms come in all shapes and sizes, most of the acoela turbellarians that intrigue Tyler are between 100 micrometers and 300 micrometers long. A few, such as Hofstenia that live in tropical mangrove swamps, can stretch up to 4 millimeters. And while the marine environment is their habitat, their homes can be in sand and mud, on algae and corals, in the interstices of polar marine ice or free-swimming in the water column. Other turbellarians, including the more familiar polyclads and planarians, reach sizes of several inches to as much as 2 feet, and range into freshwater and terrestrial habitats.

However, the size of most turbellarians isn’t proportionate to their role in the ecosystem. As top predators in the microscopic world, they control populations of other microinvertebrates and clean the sands of planktonic organisms that get filtered out of the water by wave action. Indeed, if the acoel turbellarians are as primitive as their genetic connections indicate, then concepts of how the first bottom-crawling animals reproduced and populated new habitats have to be changed, Tyler says.

There are more than 5,000 known species of these invertebrates on the planet and all of them are documented in a database begun in the late 1980s by Tyler and the late Louise Bush of Drew University. Through the years, the data have expanded considerably with the help of taxonomists in Maine and around the world, as well as graduate and undergraduate students and postdocs working in Tyler’s lab.

Because new species frequently are discovered, the task of data collection is seemingly endless. The known species of these worms are probably fewer than 10 percent of the extant species. In the lab, profiling the animals’ morphology includes lots of electron microscopy and confocal laser microscopy — the high-powered means of truly appreciating the remarkable diversity in the features of the tiny invertebrates.

“Many are discovered, but it takes a while to describe them, so that’s the bottleneck,” says Tyler. “Every time we visit a new site, we find undescribed species. Even in Maine, there are still many species of turbellarians yet to be described.

“These, like other marine worms, are still evolving and still adapting to new environments that arrive,” Tyler says.

Image Description: Images left to right, Plagiostomum sp., Belize; Eusyllis sp., California; Acanthodasys sp., Belize; Eumecynostomum evelinae, Brazil; Stomatricha hochbergi, Australia. Photos by Matthew Hooge.

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