Phylum: Arthropoda
Arthropods are the most abundant animals on earth today. There have been over 1,000,000 species described, with over 700,000 living species today. This compares to a total of 400,000 species of all other living plants and animals. There are six classes in the phylum. They all have an exoskeleton which houses the soft parts and internal organs. The reproductive, digestive, nervous, respiratory, and circulatory systems are well developed. Their bodies are usually segmented with jointed limbs.
Class Trilobita (lower Cambrian through Permian)
Trilobites were present on earth for 350 million years. During this period, over 4000 species have been identified, with very little change or adaptation from their original appearance. Trilobites are named for three longitudinal lobes of their bodies. The body is also divided into three parts: the head (cephalon), thorax, and tail (pygidium).
Class Trilobita (lower Cambrian through Permian)
Trilobites were present on earth for 350 million years. During this period, over 4000 species have been identified, with very little change or adaptation from their original appearance. Trilobites are named for three longitudinal lobes of their bodies. The body is also divided into three parts: the head (cephalon), thorax, and tail (pygidium).
Class Ostracoda (Cambrian to Recent)
They are commonly called the seed shrimp, and are represented by microscopic crustaceans. The head has two antennae, the thorax has one to three pairs of appendages. The body is enclosed by a bivalved shell.
Class Branchiopoda (lower Devonian to Recent)
This class of crustaceans is small (1/8”) in size, and may have a dorsal shield or a bivalved shell. They have ten to thirty-two trunk segments, all with paired appendages.
Class Cirripedia (Silurian to Recent)
This class of Arthropoda is represented by the barnacles. Barnacles live cemented to a fixed object with a mantle enclosing the body. The animal secretes a calcareous shell.
They are commonly called the seed shrimp, and are represented by microscopic crustaceans. The head has two antennae, the thorax has one to three pairs of appendages. The body is enclosed by a bivalved shell.
Class Branchiopoda (lower Devonian to Recent)
This class of crustaceans is small (1/8”) in size, and may have a dorsal shield or a bivalved shell. They have ten to thirty-two trunk segments, all with paired appendages.
Class Cirripedia (Silurian to Recent)
This class of Arthropoda is represented by the barnacles. Barnacles live cemented to a fixed object with a mantle enclosing the body. The animal secretes a calcareous shell.
Class Malacostraca (Cambrian to Recent)
Shrimp, lobsters, and crabs represent this class. Most are marine, but some are fresh water animals. All have eight segments in the thorax, with a shield that covers the head and thorax. Most have compound eyes.
Shrimp, lobsters, and crabs represent this class. Most are marine, but some are fresh water animals. All have eight segments in the thorax, with a shield that covers the head and thorax. Most have compound eyes.
Class Merostomata (Ordovician to Recent)
Spiders and scorpions represent the living members of this class. Their bodies are composed of a combined head and thorax region with an abdomen. They have no antennae, and the front pair of appendages is modified for feeding or poison-injecting fangs. Eurypterids are extinct animals in that class, closely related to the horseshoe crab. Some grew up to nine feet in length. Their head had two sets of eyes, and they had four pairs of walking legs.
Class Insecta (Devonian to Recent)
Insects are the largest class of arthropods, with over 900,000 species known. They are similar to other arthropods, except that they generally have wings. Insects’ body parts are: head, thorax, abdomen, one pair of antennae, three pairs of legs, and one or two pairs of wings. Fossilized insects are rare due to their exoskeleton being so thin and soft.
Spiders and scorpions represent the living members of this class. Their bodies are composed of a combined head and thorax region with an abdomen. They have no antennae, and the front pair of appendages is modified for feeding or poison-injecting fangs. Eurypterids are extinct animals in that class, closely related to the horseshoe crab. Some grew up to nine feet in length. Their head had two sets of eyes, and they had four pairs of walking legs.
Class Insecta (Devonian to Recent)
Insects are the largest class of arthropods, with over 900,000 species known. They are similar to other arthropods, except that they generally have wings. Insects’ body parts are: head, thorax, abdomen, one pair of antennae, three pairs of legs, and one or two pairs of wings. Fossilized insects are rare due to their exoskeleton being so thin and soft.