Nematode Diversity: Body Types

Last week I focused on nematode mouth structures, mostly teeth, but this week I wanted to showcase one of the key identifying features of many nematode individuals. While nematodes can have similar or the same mouth structures, it is more rare for different genera to have the same cuticle (skin) ornamentation or patterns. Much like humans, the skin diversity of nematodes is very broad, though the ornamentation can be separated into a few categories: smooth/no ornamentation, striations, punctuated ornamentation, and what I like to call textured ornamentation. Importantly, these categories are not formal categories agreed upon by the community; rather, I use these names to describe what I see even if some of them may be used by other researchers to describe another feature of nematodes.

Smooth nematodes or nematodes with no ornamentation are some of the most challenging nematodes to identify, in my opinion. Their cuticles are not patterned, which means that I have to use more minute physical features to identify them. However, I think they are good practice for recognizing differences between individuals and for recognizing nematode morphology, as they require more time and effort than other individuals.

Striations and punctuated ornamentation are the two largest categories of cuticle diversity, because they cover a broad spectrum of patterns. Striations are any ridges or lines on the cuticle that are transverse in their orientation. The thickness of striations can vary between genera or between species, and there are many genera that have striations that stop at various points throughout their bodies. The striations category also contains individuals with desmen, which are thick transverse rings made of sediment and mineral masses. Desmens come in many shapes, but a good visual example is bricks with mortar in between. Nematodes that have desmens are easily recognized because of these unique structures and look quite bulky. One key feature of striated ornamentations is that the striations are transverse and they cannot be oriented in any other direction.

Punctuated ornamentation consists of dotted structures on the nematode's cuticle. Unlike striations, dotted patterns are not always orderly. Some dotted patterns are heterogeneous where the dots are not all the same size, while some are the same size in nicely ordered rows. Sometimes, the dots can be oval-shaped, rather than round, and sometimes there are even vertical patterns mixed in. Since dot size can vary, some patterns are hard to recognize. The photo here represents a nematode from one of my samples that exemplifies this point. If you look at the blurry part of the picture on the right, the dot pattern looks like transverse lines or stripes, and so you may classify this as a genus with striated ornamentation. However, the clearer section of the image in the middle shows that the rows are dotted, not striped. I think that the dotted patterns require an eye for the fine details, and a lot of persistence, but I have learned that once you recognize a pattern or an individual genus, you don't forget.

Textured ornamentation is a category I use to describe every other nematode pattern that doesn't nicely fit into the others. I saw my first textured nematode today (sorry, no picture of it), but these individuals often have a combination of patterns on their body that look more like 3-D printed armors or interesting sculptures than traditional nematodes. These individuals are the easiest to recognize since the patterns are exceptionally unique and often don't require you to look at their mouths and other body parts before coming to a conclusion about their identities.

While we don't know for certain why nematodes have such diverse cuticle patterns, I am grateful that their individuality helps for identification purposes. I am working on identifying 2400 nematodes this summer and I would be lost without some of these minute physical features of these tiny animals.

Stay tuned for more nematode morphology next week!

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