ARTROPODA CLASSIFICATION Phylum ARTHROPODA Arthropods are bilaterally symmetrical, metamerically segmented animals having chitinous exoskeleton. Moulting is necessary for growth. They possess jointed appendages, a haemocoel or schizocoelom and have open circulatory system. Segments as well as their appendages are specialized to form various organs. Arthropods constitute about 80% of all animals. Subphylum TRILOBITOMORPHA Fossil arthropods having body divided into 3 longitudinal lobes, one median lobe and two lateral pleural lobes. Class TRILOBITA Appendages were biramous and had gills attached on them. They were abundant during Cambrian and Ordovician periods. Body was divided into cephalon, trunk and pygidium. They also possessed segmented antennae and a pair of compound eyes. Subphylum CHELICERATA First appendages are modified as chelicerae for feeding and second ones modified as pedipalps. Body is divisible into prosoma and opisthosoma, the latter is sometimes divided into mesosoma and metasoma. There are no antennae in these arthropods. Class MEROSTOMATA Body is divisible into prosoma, mesosoma and metasoma. They are marine scavengers in which abdominal appendages carry gills and telson is long spike-like. Subclass EURYPTERIDA This group includes extinct giant scorpions of Ordovician to Permian periods. They had 5 pairs of thoracic swimming appendages and 7 pairs of abdominal appendages which carried 6 pairs of gills. Metasoma was without appendages. Ex. Pterygotus; Eurypterus. They were the dominant predators of the Palaeozoic era. Subclass XIPHOSURA There are only 5 surviving species of horse-shoe crabs in the world and hence they are called living fossils. They have 5 pairs of thoracic walking legs which are chelate and armed with spines. There are 6 pairs of abdominal appendages carrying 5 pairs of book gills for respiration. Ex. Limulus or king crab. Class ARACHNIDA There are one pair of chelicerae and one pair of pedipalps and 4 pairs of thoracic legs in these arthropods. Abdomen is without legs. Breathing takes place through the book lungs or tracheal system or both. Ex. Scorpions; pseudoscorpions; spiders; ticks and mites. Class PYCNOGONIDA (=PANTOPODA) They are commonly known as sea spiders that measure 1-10 mm in length. Cephalothorax is large and segmented while abdomen is highly reduced. Legs long for crawling on the sea bottom. They are carnivores that feed on cnidarians and worms. Ex. Nymphon; Pycnogonus. Subphylum MANDIBULATA Arthropods with strong mandibles for chewing and cutting, or mouth parts are modified for different modes of feeding. They are terrestrial as well as aquatic animals. Class CRUSTACEA They possess two pairs of antennae and their body is divisible into cephalothorax and abdomen. Eyes are simple or compound. Appendages are variously modified. 1. Subclass CEPHALOCARIDA Horse-shoe shaped body without a carapace and eyes. They are marine bottom dwellers having long antennae for food gathering. Ex. Hutchinsoniella. 2. Subclass BRANCHIOPODA They are small freshwater forms with shield-like carapace and abdomen without appendages. Thoracic appendages are used for respiration. Ex. Apus; Daphnia. 3. Subclass OSTRACODA Marine and freshwater animals with laterally compressed body enclosed in a bivalve shell. Two pairs of thoracic appendages are present. Feeding and locomotion is performed by head appendages. Appendages also have respiratory function. Ex. Cypris; Cypridina. 4. Subclass MYSTACOCARIDA Body is divided into head, thorax and abdomen. Head appendages are bushy. Four pairs of thoracic appendages are present. They are filter feeders, found among sand grain in beaches. Ex. Deirocheilocaris. 5. Subclass COPEPODA Body is composed of cephalothorax and abdomen, the latter has no appendages. Single eye is present and there is no carapace. Antennae beat in rotary fashion for swimming. Some are planktonic but a large number are parasitic. Ex. Cyclops; Caligus, Monstrilla. 6. Subclass BRANCHIURA These small arthropods possess dorsoventrally flattened body adapted for ectoparasitic mode of life on fishes. Thoracic appendages are 4 pairs, used for swimming. Maxillae are used for anchoring on host. Maxillipedes are absent. There is a spine for puncturing the skin of fish. Gills are absent and abdomen has respiratory function. Ex. Argulus. 7. Subclass CIRRIPEDIA They are marine, either sedentary or parasitic. Compound eyes are absent. Thoracic appendages are 6 pairs and abdomen is rudimentary. They are commonly known as barnacles. Ex. Lepas; Balanus; Sacculina. 8. Subclass MALACOSTRACA Large crustaceans that have 5-segmented head, 8-segmented thorax and 6-segmented abdomen. Cephalothorax is covered with carapace. Compound eyes are stalked. This group includes 75% of all crustaceans. Ex. Mysis; Squilla; Palaemon; Cancer. 9. Subclass REMIPEDIA They possess long, segmented and worm-like body divided into cephalon and trunk. Trunk appendages are biramous. Two pairs of maxillae and one pair of maxillipedes are present for feeding. Found in marine caves in Bahamas. Ex. Speleonectes; Lasionectes. 10. Subclass PENTASTOMIDA They are parasitic in the respiratory system of reptiles in USA, Europe and Australia. Body is worm-like with 5 appendages on the anterior side and 2 pairs of hooks for anchoring. Trunk is ringed without appendages. Ex. Linguatula; Cephalobena. 11. Subclass TANTULOCARIDA They are ectoparasites on deep water crustaceans. There are no appendages in adult which has a bag-like body. Larva is free swimming and bears 6 or 7 abdominal somites and appendages. Adult penetrates the host skin by a mouth tube. They look similar to copepods. Ex. Basipodella; Deoterthron. Class INSECTA (=HEXAPODA) Body is divided into head, thorax and abdomen. There is one pair of antennae, 3 pairs of legs and both compound and simple eyes. Respiration takes place with tracheal system and excretion with malpighian tubules. They are the only flying arthropods. 1. Subclass APTERYGOTA (=AMETABOLA) They are primitively wingless insects that have ectognathous mouth parts and also abdominal appendages. There is no metamorphosis during development and juveniles are similar to adults in morphology as well as habits. Ex. Telson-tails; Silverfish; Spring- tails; Campodea. There are 4 orders in this group. 2. Subclass PTERYGOTA (=METABOLA) They are winged insects or lost wings later in evolution. Mouth parts are endognathous and abdominal appendages are absent. Metamorphosis is either partial or complete with a pupal stage. Ex. Dragonflies, Grasshoppers; Termites; Lice; Cockroach; Beetles; Butterflies; Moths; Fleas; Ant-lions; Scorpion flies. There are 24 orders within this group. Class CHILOPODA Medium to large carnivorous animals that live beneath stones and logs and whose body is dorsoventrally flattened and divided into head and trunk. First maxillipede is modified as poison claw. One pair of mandibles and one or two pairs of maxillae are present. Respiration occurs through tracheal system and excretion with malpighian tubules. One pair of compound eyes and one pair of antennae are present. Ex. Scolopendra; Scutigera. Class DIPLOPODA Body is cylindrical, divided into head, collum and trunk. Trunk contains diplosegments with two pairs of legs and ostia. Last segment is legless and carries anus. Slow moving, herbivorous animals that contain repugnatorial glands on the skin to repel enemies. Ex. Julius; Glomeris; Spirobolus. Class SYMPHYLA Found in humus, they are 2.0-10.0 mm long agile arthropods that run about rapidly. Body is divided into head and 14-segmented trunk. Pygidium bears an oval telson and a pair of cerci. Spiracle is single pair on the first trunk segment. Eyes are absent and mouth parts are similar to insects. Ex. Scutigerella. Class PAUROPODA Soft bodied, grub-like arthropods, less than 2.0 mm long, having cylindrical body that contains 12 segments. Eyes are absent and antennae are 3-branched. Mandibles are for piercing and grinding. Found in soil and feed on humus and fungi. Ex. Pauropus. ARTHROPODA CLASSIFICATION (After Ruppert & Barnes, 1994) 1. Subphylum TRILOBITOMORPHA – The Trilobites 2. Subphylum CHELICERATA – With chelicerae and pedipalps Class Merostomata – ex. Limulus Class Arachnida – Spiders, scorpions, mites and ticks Class Pycnogonida – Sea spiders 3. Subphylum CRUSTACEA Class Branchiopoda – fairy shrimps, brine shrimps Class Maxillopoda – Copepods Class Malacostraca – Prawn, Crabs, Lobsters, Shrimps 4. Subphylum UNIRAMIA Class Insecta – Dragon flies, Cockroach, Beetles, Bugs, Butterflies Class Chilopoda – Centipedes Class Diplopoda – Millipedes Class Symphyla – Soft bodied Scutigerella Class Pauropoda – Soft bodied Pauropus ARTHROPODA CLASSIFICATION (After Brusca & Brusca, 2003) 1. Subphylum TRILOBITOMORPHA (=TRILOBITA) 2. Subphylum CHELICERIFORMES Class Chelicerata Subclass Merostomata – Limulus Subclass Arachnida – Spiders, Scorpions, Mites Class Pycnogonida – Sea spiders 3. Subphylum CRUSTACEA Class Remipedia – Lasionectes Class Cephalocarida – Hutchinsoniella Class Branchiopoda – Daphnia; Triops Class Malacostraca – Squilla; Palaemon; Mysis; Cyamus; Crabs Subclass Phyllocarida (1 order) Subclass Eumalacostraca (15 orders) Class Maxillopoda Subclass Thecostraca – Ascothorax Subclass Tantulocarida – Basipodella Subclass Branchiura – Argulus Subclass Pentastomida – Linguatula Subclass Mystacocarida – Deirocheilocaris Subclass Copepoda – Cyclops; Monstrilla; Ergasilus Subclass Ostracoda – Cypris; Cypridina 4. Subphylum HEXAPODA Class Entognatha – Orders: Protura, Diplura and Collembola Class Insecta – 30 orders of insects Subclass Archaeognatha – Bristle tails Subclass Zygentoma – Silver fish Subclass Pterygota – 28 orders. Mayflies, termites; cockroach etc. 5. Subphylum MYRIAPODA Body contains head and long trunk bearing appendages. All are terrestrial with one pair of antennae. Compound eyes or simple eyes are present. Carnivore or herbivore animals, they include centipedes and millipedes. .