Segmented worms make up the Phylum Annelida. The phylum includes earthworms and their relatives, leeches, and a large number of mostly marine worms known as polychaetes. Various species of polychaete are known as lugworms, clam worms, bristleworms, fire worms, and, yes, sea mice. Annelids can be found in freshwater, marine and terrestrial habitats
Annelids can be told by their segmented bodies. Polychaetes (meaning "many bristles") have, predictably, many bristles on the body, while earthworms and leeches have fewer bristles. There are about 9000 species of annelid known today, but there are very few worms preserved intact in the fossil sediments. In some rare preservations, because worms have iron-containing pigments, a ghostly image of them as fossils can be seen on the surface of some very fine-grained shales.
Burrows made by worms "worm Tubes" are much more common fossils in
Arizona's Paleozoic limestones and shales.
A ghostly iron-carbon fossil image
Annelid worm teeth called conodonts. Tiny, jaw-like structures of annelid worms, called conodonts, are tiny, about the size of a small grain of sand, are found in ocean sediments laid down during the Paleozoic Era about 250 to 500 million years ago
Conodonts may have been minnow-sized, with two large eyes, with chevron-shaped markings along the body suggesting muscle bundles found only in chordates.
Here's what living conodonts might have looked like
Fossil conodont jaws seen under a microscope
Although some researchers think conodonts may have been related to the hagfish or "slime eel," these creatures were quite different from anything alive today, and conodonts are still a major mystery to paleontologists. Although complete fossils of the complete animal are quite rare, poorly preserved imprints suggest an eel-like creature with up to 7 different kinds of tooth element clustered together in the head to form a bizarre feeding apparatus unrelated to modern jaws
During the Early Paleozoic, over 450 million years ago when most of Arizona's limestone sediments were deposited, conodonts were apparently common. At that time, early in the evolution of complex lifeforms, dry land was for the most part barren, almost lifeless environment. In the ocean it was a different, and the waters were teaming with life. The wide variety in conodont teeth suggest that even at this early stage in the evolution of life, they were part of a complex ecosystem of predator and prey. What conodonts ate is a bit of a mystery because most of the creatures that made up their diet were probably soft-bodied creatures that left few fossils. Regardless of their classification, these tiny jaws give us tantalizing clues about a kind of bizarre animal that was, if nothing else, superficially worm-like in appearance.
Collecting Conodonts
Find an outcropping of well-weathered rock that contains Paleozoic fossils. Such rocks are abundant in many areas of the central United States. Many professionals use acetic acid to dissolve conodonts out of limestone.
Don't use hydrochloric acid -- it will etch and destroy the conodonts, and will etch your hands, lungs and clothing if you're not very careful. You can buy inexpensive industrial grade glacial acetic acid and cut it to 10% strength. (Use an area with good ventilation, and always use gloves and eye protection!) Break the rock into tiny-sized chunks, and put the fragments into a small bucket with holes in the bottom and soak it in a larger bucket of acid for a few days. Then lift the bucket out to drain, pour off the liquid, and repeat the process. After a few weeks, you will find enough residue to sieve, clean and inspect. In some other deposits, you can actually "pan" for conodnts much as you would look for gold. Simply scoop up some crumbling matrix and use a gold pan. The heavy enamel that makes up the conodonts remain when lightweight clays have been washed away. Once you have obtained enough residue or sediment, it is time to pan for those conodonts. Conodonts are really pretty under a 10X microscope
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