Nematodes are small, multicellular wormlike creatures.

This basic body plan might have been in the cards almost from the beginning - during the Cambrian explosion when a strange zoo of primitive multicellular creatures suddenly appeared.

"Microscopic multicellular creatures, yes," she agreed.

- "It looks like a leviathan," Bruno says, referring to the largest of the multicellular creatures in the ocean of Pup, the marginally habitable world circling Wolf 359.

As organisms became more intelligent, they grew larger, passing from the single-celled stage to multicellular creatures, and then to larger animals with differentiated cells working in groups called organs.

Then, for some reason--we will probably never know precisely why--the era of trilobites, triceratops, and other multicellular creatures commenced.

Therefore all multicellular creatures, as late arrivers, can only inhabit some topmost branches; the roots and trunk must be exclusively bacterial.

In a multicellular creature, cells are specialized for functions such as bone construction or oxygen transport.

Most of the group's specimens, dated at 580 million years, were described as tiny sponges, among the simplest of multicellular creatures.

Single-celled bacteria can form huge mat-like colonies that live almost like multicellular creatures, and evidence that such mats existed even during the earth's early years has been found in ancient rock.