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Photos: 'Hat'-Wearing Ancient Slug May Explain Mollusk Family Tree

Mollusk Family

ancient slug

(Image credit: Peter Van Roy)

The mollusk family tree has mystified scientists for decades. The mollusk group includes a diverse group of marine and land animals, including the octopus, clam and snail. Now, a fossil discovery in Morocco suggests that all mollusks descended from a mollusk with a single shell, much like the tiny, 478-million-year-old worm with a small, hat-like shell on its head. [Read the full story on the ancient mollusk]

Armored worm

ancient slug

(Image credit: Model by Esben Horn; Photo by Jakob Vinther)

This model, made out of clay, shows the 478-million-year-old armored worm. Notice the black hat-like shell on its head. Spikes covered the top of its body (A and C), and a muscle helped it move around (B), the researchers said.

Colorful fossil

ancient slug

(Image credit: Peter Van Roy; Luke Parry)

A detailed fossil of the newfound species, Calvapilosa kroegeri, next to an illustration of the creature. Notice the imprint of the radula — a conveyor-belt-like structure with teeth — at the top of the fossil.

Partial specimen

ancient slug

(Image credit: Peter Van Roy)

A partial specimen of Calvapilosa kroegeri. The fossils from Morocco are colorful because they're preserved as iron pyrite, which changes color when it interacts with water and its surrounding environment.

Just the shell

ancient slug

(Image credit: Peter Van Roy)

An isolated shell of a Calvapilosa kroegeri specimen. Mohamed ‘Ou Said’ Ben Moula, a fossil collector in Morocco, discovered these fossils in the Fezouata Biota in the late 2000s.

Tiny teeth

ancient slug

(Image credit: Peter Van Roy)

A comparison of the fossil radula of Calvapilosa kroegeri (left) and a modern mollusk (right) known as a chiton. Modern mollusks, such as snails, use their radula to scrape algae and organic matter off of surfaces. It's possible that the ancient mollusk fed on similar food with its radula.

Magnified radula

ancient slug

(Image credit: Luke Parry)

This magnified image shows the radula of a chiton, a modern-day mollusk with eight-armored shells on its back. Out of the seven specimens of the newfound Calvapilosa kroegeri mollusk, only two had completely preserved bodies. These detailed specimens, which included the radula, helped the scientists determine that C. kroegeri was the distant relative of today's mollusks.

Family tree

ancient slug

(Image credit: Luke Parry)

A newly revised family tree for the mollusk family — notice the Calvapilosa branch in the section second to the right. [Read the full story on the ancient mollusk]

Laura Geggel
As an associate editor for Live Science, Laura Geggel covers general science, including the environment, archaeology and amazing animals. She has written for The New York Times, Scholastic, Popular Science and Spectrum, a site covering autism research. Laura grew up in Seattle and studied English literature and psychology at Washington University in St. Louis before completing her graduate degree in science writing at NYU. When not writing, you'll find Laura playing Ultimate Frisbee.