BIOL 3454 1nd Edition Lecture 22 Lecture 11 3 Chapter 19 I II Trilobites Chelicerates and Myriapods Phylum Arthropoda a Roots Greek arthron joint pous or pods foot b Most diverse phylum c More than 1 1 million described and many many more undescribed d Occur in literally all habitats and every place on the surface of the earth e Hugely successful f Chitinous segmented exoskeleton a major innovation in morphology g Arthropoda subgroup relationships i Uniramous 1 branch or biramous 2 branches ii Mandible jaw insects or chelicerae spider iii 5 groups 1 Myrjapoda centipedes millipedes 2 Hexapoda insects 3 Cherlicerata spiders ticks scorpions horseshoe crabs 4 Crustacean lobsters crabs barnacles 5 Trilobite trilobites all extinct h diverse i versatile exoskeleton protective and flexible ii segmentation and appendages efficient for locomotion iii air piped directly to cells tracheal air tube system allows for a high metabolic rate possible but limits body size iv highly developed sense organs v complex behavior patterns that aid diversity of behaviors sociality and understand symbolism interactions with other organisms vi limit intraspecific competition through metamorphosis larval forms do not compete for resources don t compete w offspring i characteristics i jointed appendages ancestrally that are often modified ii bilateral symmetry with a segmented body iii triploblastic iv reduced coelom forming a hemocoel v circular exoskeleton sometimes with CaCO3 vi complete digestive system vii complex muscular system viii nervous system similar to annelids These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV V VI VII ix paired excretory glands called coxal antennal or maxillary some with excretory organs called malpighian tubules x respire through body surfaces of tracheal system xi open circulatory system Subphylum Trilobita a Probably evolved before Cambrian extinct for 200 million yrs b Poster child for fossils abundant during Cambrian and Ordovician c Dorsally flattened bottom dwellers d Can roll up like an isopod e Probably scavengers f Chitinous exoskeleton with calcium carbonate g 3 tagmata head cephalon trunk pygidium h Cephalon with 1 pair of antennae compound eyes mouth four pairs of leglike appendages i No true mouthparts Class Merostomata Subclass Eurypterida a Giant water scorpions b Thankfully extinct c Up to 3m long d From the Cambrian to the Permian e Head with 6 fused segments simple and compound eyes f Chelicerae and pedipalps g Dominant predators of the time h Anterior appendages modified into crushing claws to dent the dermal armor of early fishes Subclass Xiphosurida Horseshoe crabs a Ancient fossils from Cambrian b 4 species in 3 genera extant c Unsegmented horseshoe shaped carapace broad abdomen long rail spike called a telson d Cephalothorax with a pair of chelicerae one pair of pedipalps and 4 pairs of walking legs e Book gills for respiration tracheal system leads to book gills f 2 lateral less developed eyes and 2 simple eyes on dorsal side of carapace g Feed on worms and small molluscs h Come shore by the thousands at high tide to mate i Eggs load in a small burrow in the sand larvae resembling trilobites hatch and are washed into the sea with another high tide Class Pycnogonida sea spiders a About 100 species b Shallow to deep c Very small to 0 75m across d Small thin bodies and 4 pairs of walking legs mostly just legs e Unique feature to arthropods some segments duplicated some males have extra legs called ovigers f Circulatory system simple g No excretory and no respiratory systems h Digestive system and gonads branch into legs b c of limited space Class Arachnida a Roots Greek Arachne spider b Includes spiders scorpions psuedoscorpions whip scorpions ticks mites daddy longlegs and others c More than 80 000 described species d Amoung the first terrestrial arthropods e 2 tagmata cephalothorax and an abdomen may be segmented f Most predaceous g Chelicerae sometimes modified into fangs venom h Claws modified pedipalps i Usually helpful to humans as insect predators j A few dangerously venomous k Male pedipalps look different b c used for fertilization females still have but don t use l Spider organs and senses i Breathe through book lungs trachea or both ii Tracheal system evolved independently from that of insects less efficient iii Malpighian tubules work with unique resorptive cells in intestinal epithelium iv Some have coxal glands which are modified nephridia v Usually 8 simple eyes each with a lens optic rod and retina vision usually poor vi Many mechanoreceptors on body usually sensory setae covering body vii Hair for mechanoreceptors m Web spinning and prey capture i 2 or 3 spinnerets run to silk glands ii For their diameter spider silk is stronger than steel iii Many species use webs to capture prey but also used for nest or burrow lining wrapping prey items molting or throwing silk nets onto prey iv Some will make a wed net and toss on prey animals