Sub Phylum Chelicerata Aquatic Terrestrial Araneae Class Merostomata

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

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

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 Ancestral chelicerate Water scorpions invaded estuaries, fresh water, and are believed to be ancestors of arachnids

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

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

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

Internal Morphology of Spiders Circulatory system, respiration

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

The eyes are image-forming but simple, not compound

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

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

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

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

-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

Arthropod Phylogeny Mandibulata and Atelocerata Mandibulata and Pan. Crustacea Chelicerata Crustacea Myriapoda Hexapoda Chelicerata Myriapoda Crustacea 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 Multiramous appendages Atelocerata-Uniramia

Arthropod Phylogeny Mandibulata and Atelocerata Mandibulata and Pan. Crustacea Chelicerata Crustacea Myriapoda Hexapoda Chelicerata Myriapoda Crustacea 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 Multiramous appendages Atelocerata-Uniramia

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

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

- Homologous Compound eyes indicated by protein genetic sequence analysis; evolved in the common ancestor of pan. Crustacea - 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