Friday, January 11, 2008

Prehistoric Armoured Worms

Machaeridians are Palaeozoic armoured annelids. 2007. Jakob Vinther et al. Nature 451: 185-188.

From the press release:

The new fossil is of an machaeridian, an invertebrate that existed for about 180 million years from 485 to 305 million years ago discovered in southeastern Morocco preserves evidence of the animal’s soft tissues.

Fossil (left) and depiction (right) of extinct armored machaeridian worm. Coluors indicate the trunk (yellow), limb (red), bristles (gray), attachment of shell plates (green), gut (purple) and dorsal linear structure (blue). Credit: Vinther, et al.
The new specimen unequivocally identifies machaeridians as annelid worms, an extremely successful and diverse group of animals that includes familiar living animals like the sea mouse, the earthworm and the leech,” said Jakob Vinther.

First described over 150 years ago, armor plates of these strange animals have been found in marine fossil deposits worldwide covering the time span of their existence, and indicating that they were an important component of ancient seafloor ecosystems. Until now there was little information about their body design or how they might be related to other ancient — or currently living — animals.

This inch-long specimen that was recently discovered shows that, below the dorsal armor, the machaeridians had an elongate body with paired, soft, limb-like extensions on each segment, and two bundles of long, stiff bristles on each extension. The segmented nature of the body, and especially the presence of soft “limbs” carrying bristles, unequivocally identified the machaeridians as annelid worms, say the scientists.

According to the authors, although the exact relationship of machaeridians within the annelid worms is still uncertain, the presence of modified scales suggests that they may even belong to a group of marine bristle worms that are still in existence today.