Triloblasty

Trilobites are a well-known group of extinct marine arthropods that inhabited oceans for approximately 250 million years, from the early Cambrian period (around 521 million years ago) to their mass extinction at the end of the Permian period (about 252 million years ago). The name "trilobite" derives from the three-lobed shape of their exoskeleton, which is divided longitudinally into a central axial lobe and two pleural lobes on each side. Their fossilized remains are among the most abundant and widely distributed fossils from the Paleozoic era, providing valuable insights into early evolutionary biology and ecological diversity.

Trilobites possessed a segmented body plan, a characteristic feature of arthropods, and their exoskeletons were composed of chitin reinforced with calcium carbonate. This hard shell protected them from predators and environmental stressors, allowing them to thrive in various marine habitats, including shallow seas, deep waters, and even brackish environments. Their eyes, when present, were highly developed and often faceted, resembling those of modern crustaceans, which suggests advanced visual capabilities for detecting prey and avoiding threats.

The classification of trilobites is complex, with over 7,000 described species grouped into numerous families and orders. They exhibited remarkable diversity in size, shape, and lifestyle, ranging from small, burrowing forms to large, free-swimming predators. Some species, such as *Olenoides serratus*, had elongated bodies adapted for crawling, while others, like *Phacops rana*, had flattened forms suited for life on the seafloor. Trilobites played crucial roles in their ecosystems, serving as both prey and predators within food webs.

Their extinction at the end of the Permian period coincides with the largest mass extinction event in Earth's history, which wiped out an estimated 96% of marine species. While trilobites themselves disappeared, their legacy endures in the fossil record, offering paleontologists a window into the ancient past and the evolutionary origins of modern arthropods. Today, trilobite fossils remain popular among collectors and scientists alike, symbolizing the rich biodiversity of the Paleozoic oceans.