Trilobites are the earliest known organisms which belong to the phylum Arthropoda, a phylum which includes familiar creatures such as lobsters,crabs,insects and spiders. Trilobites are so-called because their skeleton is divided into 3 lobes. the head is called the cephalon the pygidium is the tail and the middle part is called the thorax.
Trilobites have a hard exoskelaton made out of a tough substance called chitin. the exoskeleton acts like a suit of armour, where plates move separately within the movement of the animal.
Morphology
Cephalon- its made up of several structures, including the eyes, facial sutures, free cheeks, fixed cheeks and glabella. they eyes where compound eyes . spines may be attached to the glabella. there is also an antenna.
Thorax - the thorax is made up of thoracic segments, each possessing a pair of appendages and gills in life. each thoracic segment consists of two pleurae and a segment from the axis. Each pleuron may also have spines extendidng from them, depending on the mode of life. some trilobites were so flexible that they could curl up into a ball or enroll, rather like a hedgehog. the ability to roll was a defence mechanism.
Pygidium- the pygidium or tail is composed of several segments fused together.
more on trilobites will follow soon
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