93 PALEOZOIC ARTHROPODS AND THEIR GEOLOGIC RANGES - Cambrian to Permian Trilobites crabs - Silurian to Holocene Horseshoe - Ordovician to Permian Eurypterids - Late Silurian to Holocene Arachnids - Cambrian to Holocene Ostracodes - Cambrian to Holocene Onychophorans - Devonian to Holocene Insects 94 SUBPHYLUM TRILOBITA - TRILOBITES characteristics: Chief has three-lobes Body composed of chitin, with calcium carbonate Skeleton is divided into three segments: Body head segment - cephalon Rigid flexible middle section - thorax Jointed, tail piece - pygidium Rigid FIGURE 12-42 95 SUBPHYLUM TRILOBITA - TRILOBITES Trilobite "three" (tri) + "lobed" (lobus). Name: range: Cambrian to Permian Geologic of life: Exclusively marine. Most were bottom dwellers living in shallow shelf Mode environments. 96 CLASS EURYPTERIDA - EURYPTERIDS scorpion-like or lobster-like arthropods. Extinct Predators. to 10 ft long. Up Ordovician to Permian. Most are Silurian or Devonian. Geologic of life: Inhabited brackish estuaries. Mode 97 CLASS ARACHNIDA - ARACHNIDS spiders, ticks, and mites Scorpions, are the oldest arachnids with a fossil record. Scorpions had evolved by Late Silurian. The earliest ones appear to have lived in the Scorpions water, because their fossils have gills. spiders, and mites are found in Devonian rocks. Scorpions, Late Silurian to Holocene. Geologic 98 CLASS OSTRACODA -OSTRACODES ostracodes are mainly microscopic in size. The bivalved shell encasing a shrimp-like creature. Tiny range: Cambrian to Holocene. Geologic of life: Both marine and freshwater. Mode 99 CLASS ONYCHOPHORA
93 PALEOZOIC ARTHROPODS AND THEIR GEOLOGIC RANGES Trilobites - Cambrian to Permian Horseshoe crabs - Silurian to Holocene Eurypterids - Ordovician to Permian Arachnids - Late Silurian to Holocene Ostracodes - Cambrian to Holocene Onychophorans - Cambrian to Holocene Insects - Devonian to Holocene 94 SUBPHYLUM TRILOBITA - TRILOBITES Chief characteristics: Body has three-lobes Skeleton composed of chitin, with calcium carbonate Body is divided into three segments: Rigid head segment - cephalon Jointed, flexible middle section - thorax Rigid tail piece - pygidium FIGURE 12-42 95 SUBPHYLUM TRILOBITA - TRILOBITES Name: Trilobite "three" (tri) + "lobed" (lobus). Geologic range: Cambrian to Permian Mode of life: Exclusively marine. Most were bottom dwellers living in shallow shelf environments. 96 CLASS EURYPTERIDA - EURYPTERIDS Extinct scorpion-like or lobster-like arthropods. Predators. Up to 10 ft long. Geologic Ordovician to Permian. Most are Silurian or Devonian. Mode of life: Inhabited brackish estuaries. 97 CLASS ARACHNIDA - ARACHNIDS Scorpions, spiders, ticks, and mites Scorpions are the oldest arachnids with a fossil record. Scorpions had evolved by Late Silurian. The earliest ones appear to have lived in the water, because their fossils have gills. Scorpions, spiders, and mites are found in Devonian rocks. Geologic Late Silurian to Holocene. 98 CLASS OSTRACODA -OSTRACODES The ostracodes are mainly microscopic in size. Tiny bivalved shell encasing a shrimp-like creature. Geologic range: Cambrian to Holocene. Mode of life: Both marine and freshwater. 99 CLASS ONYCHOPHORA
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