The name "orthoceras" means "straight horn" and refers to the creature's long, conical shell.
In these shells lived Orthoceras, an ancient mollusk whose fossil shells are found and polished in the Sahara Desert of Morocco.
The siphuncle is a tube which ran the length of the Orthoceras's shell. By filling the siphuncle with water, the orthoceras could then use its muscles to force the water out and propel itself through the water. You can see this jet propulsion in action in the video below which shows a Nautlius found in today's oceans:
Like the Nautilus shown above, Orthoceras used its siphuncle to control bouyancy as well. By controling the ratio of air to water in the siphuncle, Orthoceras could move up and down in the water.
Orthoceras's soft body lived in the open segment at the end of it's shell. As its body grew, and that part of the shell became too small, a dividing partition called the septa grew to separate the old "home chamer" from the new one. Orthoceras grew as large as 14 feet!
In the Devonian geologic period, some 350 million years ago, these ocean dwellers, reaching a length of over 6 feet, swam in an Ocean which covered the area. After death, their shells were preserved in the black marble where they are found today.
Orthoceras fossils have an iridescent gemlike quality when polished and because of their incredible age and beauty make for unique display pieces and jewelry.