Trilobite

Trilobite

The Trilobite is a marine animal from the Trilobita

 class and Arthropod  phylum. The word Trilobite means three lobes, and it is one of the extinct marine creatures. It possesses hard shells and segmentation, which differentiates it from others.The group Trilobite has over 150 families, and is composed of 10 orders. Around 20,000 species and 5,000 genera belong to the Trilobite phylum.Hence, it is the most diverse group of arthropods with varying differences in sizes and forms in each species. The largest species grows at least 30 to 70cm long, whereas the small species are found below a millimeter in length.The fossils of the Trilobite generally consist of the exoskeleton and the other soft parts like gills, legs, and digestive and musculature parts. But the soft parts are very rarely found. Still, there are a very few locations where the soft body parts are preserved.

Anatomy

The name Trilobite refers to these animals due to the presence of 3 body parts. Though the species are found in different shape and size, basically their body structure is similar. The three body parts are the head or Cephalon, thorax with segmentations, and the tail piece referred as pygidium. The other body parts are the long axial lobe in the center with flanking pleural lobes on the left and right side. Some believe, it gained the name due to these three lobes running from the Cephalon till the tail part. The mouth is situated near the hypostome, whereas the opening of the anus is found in the rear part of the pygidium. The skeleton is a good source of calcite (CaCO3).. Usually it is found to range from 1 millimeter to 30 centimeters. Till now, the largest Trilobite species recorded had a length of about 72 
cm.

Distribution

The Trilobite was mainly a marine creature, as its fossil remains were often acquired from the rocks that possessed the fossils of the other animals from the salt water habitat such as Crinoids, Brachiopods and Corals. It was found in shallow as well as deep water from the marine paleoenvironment.

Reproduction

It is believed that the Trilobite animals reproduce sexually, similar r to the modern arthropods. Some species lay fertilized eggs, whereas some species were found with a brooding pouch in the swelled Cephalon. This appears to lead to  a conclusion that those species used to brood the eggs or the young ones inside the body. After the hatching of the eggs, the young ones are developed with the exoskeleton, which is molted in each stage of their growth.

Fossil Records

The fossil records of the Trilobite creature belong to the Early Cambrian period that is about 521 million years back. They flourished throughout the period of the Paleozoic, and later experienced severe extinction by the Devonian era. The Proetida species were the only species that did not become  extinct in that era. But again,  by the end of the Permian era, the mass extinction caused the remaining species to become extinct. Before their appearance in the fossil records, this group of creatures had a wide diversity of species, and was distributed equally around the globe. The exoskeleton which gets easily fossilized, was acquired as the fossil. An extensive collection of around 17,000 fossilized exoskeletons, belonging to the Paleozoic time was acquired. The Bigotinids, Redlichiids and Fallotospid species are the three Trilobites fossil found initially, which belonged to 540 million years ago.