Arthro II - RECALL general characteristics of arthropods...

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1 Arthropoda II: myriapods & hexapods RECALL: general characteristics of arthropods: bilateral symmetry, metameric, tagmosis (fusion of metameres into regions) paired, jointed appendages (primitively one pair per segment) exoskeleton (= hard, chitinous cuticle) reduced “true” coelom & persistent blastocoel (= hemocoel) complete digestive system (mouth, anus) open circulatory system respiration by various, specialized structures paired excretory organs of various sorts nervous system with double nerve chain of ventral ganglia sexes usually separate (dioecious), with paired reproductive organs protostomes Phylum Arthropoda Class Merostomata Class Pycnogonida Class Arachnida Subphylum Trilobita Subphylum Chelicerata Subphylum Crustacea Class Branchiopoda Class Malacostraca Class Copepoda Class Ostracoda Class Cirripedia Subphylum Uniramia Class Chilopoda Class Diplopoda Class Hexapoda (Arthropoda II) Subphylum Hexapoda Subphylum Myriapoda old, “traditional” split among Arthropoda BIRAMOUS UNIRAMOUS “uniramian” characteristics Circulatory System • open circulatory system consisting of a hemocoel filled with hemolymph (blood); the hemoceol is a remnant of the blastocoel ; this is the main body-cavity in arthropods – the true coelom is reduced to small areas housing gonads & sometimes excretory organs • appendages are unbranched (so just one branch) • 1 pair of antennae • mandibles (“jaws”) present • 2 pairs of maxillae (usually) • body is covered with a (waxy) cuticular exoskeleton
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2 arthropod “open” circulatory system: dorsal contractile heart open circulatory system in arthropods : blood empties into sinuses to bathe organs and tissues and returns directly from the hemocoel to the heart through ostia basic mouthparts anatomy mandibles maxillae labium highly specialized insect mouth parts are “derived” (specialized) appendages Gas Exchange • tracheal system (consists of thin-walled tubes) • tracheal tubes open to the outside by (valved) spiracles • if juveniles are aquatic, they may have gills spiracles
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3 tracheae on insect midgut tracheal system of an insect = a system of air tubes (tracheae ) extending from surface spiracles (openings) carries air to and from tissues complete with regional specialization Digestive System foregut midgut (where absorption of nutrients takes place) hindgut inner cuticle lining (gets molted as well) Excretion malpighian tubules -at the end of the hindgut; insects resorb water along with K + & Na + ions *allows insects to conserve H 2 O & withstand terrestrial environments* malpighian tubules (of a cockroach) INSECT start here malpighian tubules (of a cockroach) end here
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4 Reproduction • separate sexes • usually internal fertilization (terrestrial!) a few show maternal care sexual cannibalism in some (YouTube) FLIGHT!
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  • Summer '10
  • spears
  • Merostomata Class Pycnogonida Class Arachnida Class Branchiopoda Class Malacostraca Class Copepoda Class Ostracoda Class Cirripedia Class Chilopoda Class Diplopoda Class Hexapoda, Subclass Pterygota

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