I traveled to a marine research station on a picturesque Swedish fjord many times during the four years I worked on my doctoral degree. What took me back again and again? Buried in the mud off Sweden’s west coast lives a small orange-brown worm, which to the untrained eye looks completely insignificant.
The fact that I devoted so much study to this boring mask was a source of great pleasure for my friends. For them and perhaps for most people, the word worm evokes the idea of a fat pink earthworm. So why sift lots of mud from a freezing Swedish fjord to find a handful of animals I could dig up in the garden?
Broadly defined, a worm is a relatively small soft animal, but there is an incredible amount of diversity in this group. These animals live all over the world, and some of them are remarkably resistant; they are found in habitats ranging from hydrothermal vents to lakes that are three times saltier than the ocean. “Mask” is really a collective name for a large number of animals with different characteristics that span the trees of life.
This diversity means that researchers from many different disciplines are interested in many different species of worms. For example, my worm from the fjord, called Xenoturbella bocki, has a central position for understanding the development of animals.
At first glance, you might think that people and all these worms have very little in common. But really, many worm species provide researchers with opportunities to conduct basic research on cells and systems that can be translated into information about our biological origins and even relevant applications for human development and health.
Regeneration
If you chop off your head, you will not grow a new one. But if you were a face mask, you would not only grow a new head – your head would also grow a new body. Cut one of these striking worms into hundreds of small pieces, and you will have hundreds of new animals. Planaria is truly the masters of renewal.
To achieve this performance, both the instructions and the material to construct a new body must be present in each of these fragments. These building blocks are called neoblasts: stem cells distributed through the worm which has the potential to become an adult cell type.
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Planarian regeneration research has some surprising applications. Researchers can investigate which genes keep neoblasts in a flexible state or lead them to become specific cell types during the regenerative process. This research does not help researchers learn to recreate new human heads, but it can inform theirs understanding of wound healing or suggest new goals for cancer research.
If there was a price for the most unfortunate worm, it could go to the name says “everything” penis worms, formally known as Priapulida. In fact, their unfortunate appearance makes priapulids very well adapted to dig into the soft sediment where they live.
This behavior leaves a valuable legacy. The fossilized traces of digging worms represents some of the most important fossils recovered from the Cambrian era. The first early representatives of most of the large groups of animals date to this geological period, which began about 540 million years ago. Evidence suggests that priapulid-like worms created these track fossils as they dug into the soft ground where they lived.
These ancient ancestors mean that Priapulids have been described as “living fossils.” Studying their evolutionary genetics provides an insight into the ancient origins of the various cell types and organs we find in animals today.
For example, by understanding how modern priapulids make the intestines, researchers can draw conclusions about evolutionary processes and genes that shaped the intestines of animals that lived hundreds of millions of years ago. Then researchers can better understand how different animals have refined and modified what their gut looks like and how it is patterned in response to their environment and diet.
Where did the eyes come from?
Even Charles Darwin, development of the eye posed a conceptual problem. How could such a complex structure have arisen through natural selection?
A relative of the earthworm and leech, an annelid called Platynereis dumerilii, turns out to be an important animal for understanding how it happened. Platynereis develops particularly slowly and, similar to priapulids, provides a window into features found in our very ancient ancestors.
Platynereis larvae have one of the simplest eyes in the animal kingdom: a two-cell structure consisting of a photoreceptor that can detect light and a pigment cell. But it has an additional type of photoreceptor in its larval brain – one that is also found in the vertebrate’s eye. This suggests it both of these photoreceptor types was present in an ancestral animal. By examining how Platynereis uses these cells, researchers can hypothesize the steps by which cell types and circuits were eventually integrated to create the spinal eye.
The worm world extends far beyond the humble earthworm in your backyard: there are literally millions of different species living all over the world. The examples described here are just a small representation of the diversity and unexpected scope that research on these critics may have.
Author: Helen Robertson – Postdoctoral Fellow in Organismal Biology and Anatomy, University of Chicago 
Source: sn.dk