Nematode Diversity: Amphids

This week I've worked on more of the nematodes from my samples, and I have identified (or tried to identify) nearly 600 individuals. Last week I showed off the amazing diversity of nematode skin patterns, but this week I want to talk about their amphids. Nematodes are rather simple organisms in regard to their organs and physiological structures, though they do have body parts recognizable in many animals, including mouths (with occasional jaws and teeth), guts, reproductive parts, and tails. However, unlike most organisms, nematodes have an external sensory organ known as the amphid. The amphid is an olfactory, chemoreceptive, and thermoreceptive sensory organ that comes in a variety of shapes and sizes. While this organ's function has been well described for the terrestrial nematode C. elegans (this is one of the most common model organisms), we don't have a strong understanding of its function across nematode taxa.

Like nematode skin patterns, there are various shapes and forms that nematode amphids can take, including circular, spiral, cup-shaped, and even some unique shapes like the one seen here resembling a pretzel. These organs are helpful when identifying nematodes, as some amphid shapes are unique to genera. Amphid shapes can also be deceptively tricky, as the circular shapes are usually misleading. As there are four different circular shapes that look alike, using high powered microscopy is important in the identification process.

If you examine the image below, you will see the circular amphid at the head. At first glance you might call this amphid a circle, but if you look closely at ~10:00 on that circle, you will see that there is a break. This is one of the more challenging shapes to differentiate from the traditional circle, as the breaks can be quite elusive and you may only see the breaks at a certain focal plane. Such subtle differences, however, are valuable as researchers compile evidence to support their claims about the identity of nematodes. So if you are keeping track, we have used the presence/absence of teeth, the skin/cuticle texture pattern, and now the amphid shape to help identify the nematode. Next week I will talk about the last feature that is exceptionally useful when identifying nematodes, and that's the shape of the reproductive organs. Stay tuned to get the final puzzle piece in identifying nematode genera.

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