The correct answer is A. Trilobites are extinct arthropods.
Explanation:
Trilobites are an extinct animal group that existed during the time period in earth history that extends from Cambrian to the end of the Permian. The only trilobite trace that exists today is in the form of fossils and trace fossils.
They were marine arthropods, most of which were benthos. Due to the presence of the outer skeleton and the marine way of life, a large number of trilobite fossils have been preserved. Today, about 15,000 species of trilobites are known.
