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Phylum Arthropoda Phylum Arthropoda • “Jointed Foot” • Crabs, lobsters, spiders, ticks/mites, insects, centipedes, millipedes • 85% of all known species • Developed from Annelids • First land animals some 300 million years ago. Characteristics that make Arthropods successful 1.Metamerism 2.Exoskeleton 3.Appendages 4.Hemocoel 5.Metamorphosis Metamerism • Segmentation of body into metameres modified by tagmatization (specialization) of segments • Tagmata: head, thorax and abdomen. • All segments are integrated into a single functioning unit. Exoskeleton • Made up of chitin (protein) • Provides support, protects, and minimizes water loss. • Does not grow with animal so must molt or ecdyse – Vulnerable to attack or drying out after the molt • Heavy compared to body • Move by contracting muscles against exoskeleton Appendages • Paired, jointed appendages adapted to function in: – sensing their environment – defending against predators – swimming – walking – grasping – transferring sperm – generating water movement – gas exchange Hemocoel • Reduced coelom • Open circulatory system • Like their exteriors, the internal organs are generally built of repeated segments. • Ventral nervous system is “ladderlike” with paired nerve cord running through all segments and forming ganglia • Complete digestive tract Metamorphosis • The changes in form that occur as approach adulthood Incomplete (Simple) Metamorphosis • Juveniles and adults are similar in appearance, differ only in size • Egg Nymph Adult Complete Metamorphosis • Juveniles and adults have different forms, often live in different habitats, and may have very different behavior. • Egg Larvae Pupa Adult (most) • Reduces competition between larval and adult stages! Five Subphyla of Arthropoda 1. Trilobitomorpha (extinct) 2.Chelicerata 3.Crustacea 4.Myriapoda 5.Hexapoda Phylum Arthropoda: Subphylum Chelicerata • Over 60,000 species • Possess chelicerae (fangs) 1. Class Merostomata 2. Class Arachnida – Order – Order – Order – Order Scorpionida Araneae Opiliones Acarina 3. Class Pycnogonida Phylum Arthropoda Subphylum Chelicerata Class Merostomata • Horseshoe crabs • Similar to extinct trilobites and present day scorpions • 4 species • Covered by hard horseshoeshaped carapace • Blood used to create bacterial test Phylum Arthropoda Subphylum Chelicerata Class Arachnida • Spiders, scorpions, ticks, mites • Mainly terrestrial • Two body regions 1. Cephalothorax 2. Abdomen • Eight legs (4 pairs) • Two other appendages attached to cephalothorax 1. Chelicerae: claw-like fangs inject poison 2. Pedipalps: aid in feeding and sensory • Up to 12 simple eyes (most have 8) detect light Phylum Arthropoda Subphylum Chelicerata Class Arachnida Order Scorpionida • Scorpions • 800 species • Greatly enlarged pedipalps to catch and hold prey • Abdomen tapers down to stinger – injects venom • Tropical areas • Secretive and nocturnal Phylum Arthropoda Subphylum Chelicerata Class Arachnida Order Araneae Spiders 34,000 species All venomous Sensory setae over entire body: detect movement and pressure • Skillful hunters • Webs formed by spinnerets – secrete strong, elastic protein • • • • – Silk used to line nests, cradle young, hold eggs and sperm, and for ballooning Order Araneae • Feed by injecting enzymes into prey to dissolve body substance and suck out liquefied remains • Excretion (uric acid) through malipighian tubes • Two Respiratory Strategies (most have both) 1. Oxygen carried through body by tracheae (tubes) and spiracles (slits in skeleton) 2. Blood circulated through book lungs (paged) like gills • Reproduction : Dioecious, solitary, complex mating – Pheromones produced – Internal fertilization – sperm on pedipalps enter under female abdomen – Oviparous – eggs hatch in about 2 weeks Phylum Arthropoda Subphylum Chelicerata Class Arachnida Order Opiliones • “Daddy Long Legs” • 6,500 species • Omnivores & Carnivores • 1 segment, 2 eyes Phylum Arthropoda Subphylum Chelicerata Class Arachnida Order Acarina • • • • • • Ticks and Mites 30,000 species Very small (some<1mm) One body segment Many carry diseases Mostly parasitic: attach to skin and feed on blood Phylum Arthropoda Subphylum Crustacea • Mostly marine • Chewing jaw called mandibles • Two pairs of antennae 1. Class Malacostraca – Order Decapoda 2. Class Branchiopoda 3. Class Maxillopoda – Subclass Copepoda – Subclass Cirripedia Phylum Arthropoda Subphylum Crustacea Class Malacostraca Order Decapoda • Crabs, crayfish, shrimp, lobster • 15,000 species • “Ten legs” • Numerous segments grouped into cephalothorax & abdomen • Maxillae: Used for holding food • Maxillipeds “jaw feet” – Modified as mouthparts to hold food and senses touch/taste • Periopods: 4 pairs of “walking legs” – One pair with Chelipeds (claws) – Bear the gills • Pleopods: 5 pairs “swimming legs” – Swimmerets: • used for swimming, water movement over gills, and reproduction (bear the sexual organs) – Uropod: • Fused swimmerets used as flipper/tail fin Phylum Arthropoda Subphylum Crustacea Class Branchiopoda • Water flea, tadpole shrimp, clam shrimp, brine shrimp or “sea monkey” • Primarily freshwater • Many produce “winter eggs” that hatch in spring Phylum Arthropoda Subphylum Crustacea Class Maxillopoda Subclass Cirripedia • • • • Barnacles Sessile Mostly monoecious Highly modified Phylum Arthropoda Subphylum Myriapoda • • • • • • Centipedes and millipedes Over 13,000 species Single pair of antennae Simple eyes Mandible Between 10 to over 750 legs 1. Class Diplopoda 2. Class Chilopoda Phylum Arthropoda Subphylum Myriapoda Class Diplopoda • Millipedes • 11 to 100 trunk segments with 2 pairs of legs/segment • Rounded body • Found mainly in tropical areas • Feed on decayed plants • Excrete foul-smelling or toxic substances from stink glands Phylum Arthropoda Subphylum Myriapoda Class Chilopoda • Centipedes • 15+ segments with 1 pair of legs each • More flattened body • Some very colorful • Poison claws • Fast moving predators