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Sub Phylum Chelicerata

Sub Phylum Chelicerata. Aquatic Terrestrial. Araneae. Class Arachnida. Class Merostomata. Acari. Ticks, mites. Scorpiones. Class Pycnogonida. Eurypterids 450 to 250 mya (water scorpions) Largest arthropods ever known (largest nearly 3 m)

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Sub Phylum Chelicerata

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  1. Sub Phylum Chelicerata Aquatic Terrestrial Araneae Class Arachnida Class Merostomata Acari Ticks, mites Scorpiones Class Pycnogonida

  2. Eurypterids 450 to 250 mya (water scorpions) Largest arthropods ever known (largest nearly 3 m) Many features in common with modern scorpions and horse-shoe crabs With book gills similar to those in horseshoe crabs

  3. Eurypterids 450 to 250 mya Largest arthropods ever known (largest nearly 3 m) Many features in common with modern scorpions and horse-shoe crabs Xiphosura Arachnida Pycnogonida Eurypterida Water scorpions invaded estuaries, fresh water, and are believed to be ancestors of arachnids Ancestral chelicerate

  4. vinegaroon Microwhip scorpion Spiders Whip scorpions False scorpions True scorpions are also arachnids but distantly related

  5. Permian Arachnids 332 mya With silk producing spigots but lacking spinnerets Segmented whip; links the spiders to whip scorpions

  6. Chelicerata Body Plan Order Araneae as a model • Body as anterior prosoma and post. Opisthosoma (abdomen) • First anterior segment with no appendages • Second segment with clawed “chelicerae” (or fangs) • Other head appendages are “pedipalps” • No mandibles

  7. Internal Morphology of Spiders Circulatory system, respiration

  8. Internal view of a book lung showing high surface area for oxygen exchange

  9. The eyes are image-forming but simple, not compound

  10. Internal Morphology of Spiders Digestive system and excretory system midgut Pumping stomach mouth

  11. Phylogeny of Arthropoda Nearest relatives? Mono or polyphyletic? Relationships within the group?

  12. Cephalocarida(12 spp) • -2-4 mm in sediments • Blind • No abdominal appendages • 2nd antennae behind the mouth? • (as common in embryonic crustacea) • Remipedia(24 spp) • -10-40 mm in sediments • Blind • Head and trunk • w/42 segments • Swim upside down

  13. On the Phylogeny of Arthropoda A monophyletic lineage of the Ecdysozoa clade Onychophora is the sister group of Arthropoda

  14. -Protocerebrum and deutocerebrum also in Onychophora -But tritocerebrum is a unique character of Arthropoda -Position of cerebrums helps establish homology of segments and segmental appendages

  15. Arthropod Phylogeny Mandibulata and Atelocerata Mandibulata and PanCrustacea Chelicerata Chelicerata Crustacea Myriapoda Myriapoda Crustacea Hexapoda Hexapoda • Homology of mandible widely accepted. • Is possession of uniramous appendages and a single pair of antennae {Atelocerata = without back horns (or antennae)} a shared derived character? Mandibles Atelocerata-Uniramia Multiramous appendages

  16. Arthropod Phylogeny Mandibulata and Atelocerata Mandibulata and PanCrustacea Chelicerata Chelicerata Crustacea Myriapoda Myriapoda Crustacea Hexapoda Hexapoda • Homology of mandible widely accepted. • Is possession of uniramous appendages and a single pair of antennae {Atelocerata = without back horns (or antennae)} a shared derived character? - Insect fossils found with polyramous appendages - Land Crustacea w/single pair of antennae & uniramous append. - Buds of second antennae in insect development - Buds of abdominal appendages in insect development Mandibles Atelocerata-Uniramia Multiramous appendages

  17. Letter Nature 463, 1079-1083 (25 February 2010) Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences Mandibulata Chelicerata? Myriapoda? Pancrustacea?

  18. Inferences: Mandibulata? Myriapoda? Hexapoda? Entognatha? Insecta? Crustacea?

  19. Homologous Compound eyes indicated by protein genetic sequence analysis; evolved in the common ancestor of panCrustacea • - Hemocyanins present in malacostracans also known in cockroaches and grasshopper embryos • JH and Methyl farnesoate production…hormones involved in molting and growth, utilize many of the same enzymes • Have the same set of micro RNAs

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