A large group of arthropods abundant in the Paleozoic seas. They had segmented exoskeletons divided into three lobes.
Ancient marine arthropods, abundant in the Early and Middle Palaeozoic but extinct since the Permian Period. Their name is derived from the three lobes running the length of the body. They had paired, gill-bearing limbs and compound eyes. Sizes ranged from a few millimetres to about 90 cm.
A group of benthonic, detritus-feeding, extinct marine invertebrate animals (phylum Arthropoda), having skeletons of an organic compound called chitin.
A peculiar group of extinct Crustaceany, somewhat resembling the Woodlice in external form, and, like some of them, capable of rolling themselves up into a ball. Their remains are found only in the Palaeozoic rocks, and most abundantly in those or Silurian age. Trimorphic: Presenting three distinct forms.
ancient arthropods having a hard outer skeleton, and which became extinct over 200 million years ago.
A peculiar group of extinct Crustaceans, somewhat resembling the Woodlice in external form, and, like some of them, capable of rolling themselves up into a ball. Their remains are found only in the Palæozoic rocks, and most abundantly in those of Silurian age. 214
