Trilobites; way of life.
The trilobites are extinct arthropods which lived in the sea from the Cambrian through the Permian. Most forms probably lived close to the sea floor, and we know both walking- and digging trails made by trilobites. Some were mud-eaters, others were carnivorous. Those that ate other animals, had legs bearing strong spines, which could seize the prey, crush it and bring it forward to the mouth. Forms having thin shell, long spines and large eyes, often have a wide geographic distribution, which suggests that they were planktonic (floated freely in the water masses).
An outer skeleton (exoskeleton) was common to all trilobites. This consisted of a head shield (cephalon), a tail shield (pygidium) and a segmented body shield (thorax). Seen from above, the shield is divided into three longitudinal areas ("lobes"). This explains the name Trilobita.
In some forms, the shield was constructed such that the trilobite could enroll. In that way they could protect the less solid ventral side, where the mouth, the limbs and the gills were situated. Other forms were uncapable of enrollment. They probably could bury themselves in the sediment for protection.
Some forms were blind, but most had large eyes, which were built up from many small lenses. The eyes of the trilobites are the oldest known visual organs.
The limbs are very seldom preserved, and therefore they are less known. With the exception of one pair of antennae at the front, and in some forms also at the back, all the limbs were two-branched, with a segmented walking leg and one gill branch.
During growth the trilobites, like all arthropods, periodically shed their old shell and developed a new and larger one. Most of the trilobite remains that we find are remains after such shell-shedding (exuviation or molting). List of contents in the trilobite showcase
Publisert 18. mai 2011 16:00