ScienceWise - Nov/Dec 2006

Creatures of the Sand

The worm pictured above looks like it belongs in a sci fi horror flick but it actually originated from a sandy beach down at Broulee on the south coast. It’s named Enoplolaimus and it’s just under a millimetre in length. Enoplolaimus is a nematode (sometimes called roundworms) and this particular form hasn’t been given a species name yet.

There’s a whole world of tiny organisms that make their life in between grains of sand. They are referred to as the meiofauna, and Dr Warwick Nicholas, a Visiting Fellow at the School of Botany and Zoology, has been documenting them for many years.

“Since I retired in 1991 I have been systematically examining the meiofauna of Australian estuaries and beaches,” says Dr Nicholas. “No one has previously done this systematically in Australia, although it has been well covered in other parts of the world. Most Australian species are new to science. The fauna includes copepods, turbellaria, ostracods, archiannelids, tardigrades and acarina, but by far the most numerous are nematodes.”

The image show here was prepared using a scanning electron microscope (SEM) at the ANU Electron Microscope Unit (EMU). Preparing soft and delicate forms for the electron microscope takes a bit of effort because they are scanned in a vacuum. First, Dr Nicholas prepares his specimens by re-suspending a sample of sand in tap water.

“I then collecting the meiofauna it contained on a 60 micron mesh sieve and back wash in sea water into a petri dish,” he explains. “The sample is fixed in 5% formalin in sea water, and then the desired specimens are picked up with a micropipette under a binocular microscope. The selected specimens are washed in distilled water and placed individually in a drop of water on a 10 cm diameter copper disc.

“The drop is frozen by placing the disc on a metal stand cooled with liquid nitrogen. The disc then goes into the EMU freeze drier overnight. Double-sided adhesive tape is affixed to SEM metal stubs and the nematodes or other meiofauna are picked up with a fine needle under the microscope and placed tail down on the adhesive tape. The stub, with specimen in situ, is coated with gold/ palladium in the EMU coating unit, then examined in the SEM.”

Besides displaying such an evocative form, the image of Enoplolaimus is also significant in that it was one of the first captured by the EMU’s new Field Emission Scanning Electron Microscope. The new machine is a Hitachi 4300 Schottky Field Emission SEM and is expected to be become one of the workhorses of the Unit.

“The Hitachi 4300 FESEM is a fabulous new addition to the EMU,” says Dr Sally Stowe, Coordinator the of EMU. “It’s a simple, robust and wonderfully flexible machine that will be serving many of our users needs over the coming decades. When fully configured it will incorporate a cold stage, cathodoluminescence detector and energy dispersive X-ray facility.

“One of the aspects that makes it particularly suited to imaging intricate specimens like these nematodes is its ability to operate with a relatively poor vacuum around the subject being scanned. Traditionally SEMs operate in a high vacuum making specimen preparation extra tricky. The Hitachi 4300 is more forgiving. Also, because it’s a poor vacuum you don’t get so much charging of the fine structures like the feelers around the nematode’s mouth. In our older SEMs these feelers would usually have been glowing brightly often making it difficult to record the image.”

Besides working on the taxonomy of Australia’s meiofauna, Dr Nicholas has also been investigating the ultrastructure and ecology of nematodes. While the work makes a valuable contribution towards understanding a little known aspect of Australia biodiversity, it is entirely self-funded.

“This work would be quite impossible without the support of Sally and the staff of the EM unit,” says Dr Nicholas. “It’s a great facility making an important contribution to a wide range of research being undertaken across the campus.”

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