Marb 435 1st Edition Lecture 17 Current Lecture Arthropoda 1 Phylum Tardigrade About 800 species Generally only 100 150 m some up to 1 5 mm Habitats Marine interstitial Freshwater Terrestrial moss leaf litter soil Capable of cryptobiosis Can live up to 100 years Criptobiosis Death like state of suspended animation hidden life Under adverse conditions extreme temperatures desiccation animals can remain dormant for years Re animation takes 10 min to several hours PHulum Onychophora Aka velvet worms Terrestrial and worm like 110 species Tropical or temperate Live in leaf litter or underneath logs or other objects Smooth body surface with chitinous cuticle and papillae 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 No external segmentation but have segmented organs Appendages lobopods Ostia Nephridia Ganglia Feeding Predators of small arthropods Shoot jets of slime from their oral papillae Slime denatures into a sticky substance which conveniently does not stick to the onychophoran cuticle Phylum Arthropoda Estimates of species number vary greatly Represent at least 60 of all living species and at least 70 of all animals At least 1 million described species Inhabit practically every imaginable environment Marine Freshwater Terrestrial Aerial segmented body with tagmatization chitinous exoskeleton with molting Paired and jointed segmental appendages Absence of locomotory cilia Have setae different structure and development than annelid chaetae Main body cavity is a hemocoel Evolutionary success story One out of three animal taxa with powered flight The most successful colonizers of terrestrial habitats Tagmosis Tendency to organize segments into regions with similar structure function and appendages Basic tagmata head Thorax and abdomen Exoskeleton Secreted by the epidermis Consists of protein and alpha chitin a polysaccharide molts Can be rigid or flexible Body wall musculature and connective tissue are reduced Commercial interest in chitin Strong nonallergenic and biodegradable Fabrics and surgical sutures Biodegradable capsules for drugs Food additive might reduce caloric and cholestorol uptake Ecdysis molting Exoskeleton is secreted by the epidermis and hardens To increase in body size the arthropod must shed the old cuticle secrete a new one and harden it Process Controlled by ecdysteroid hormones Increase in body pressure by uptake of air or water splits the old exoskeleton New cuticle is partially in place before the old one is shed Muscular and nervous system o Arthropods Each muscle fiber may be innervated by up to five different types of neurons Each neuron may innervate multiple muscle fibers Strength of muscle contraction depends on the rate of neuron firing Some nerve muscle connections are inhibitory o Vertebrates Each muscle fiber innervated by a single motorneuron Each motorneuron connects to a single muscle fiber Strenth of muscle contraction depends on the number of fibers contracting in a muscle Nerves always stimulate muscle contraction Appendages Paired jointed segmental appendages are a synapomorphy for arthropods Appendages consist of a series of articles that can be moved relative to each other by flexor and extensor muscles Body cavity and circulation Open blood vascular system blood hemolymph leaves the heart through closed vessels it enters the heart through perforations ostia Body cavity is a hemocoel Excretion Saccate Nephridia Typical for aquatic arthropods but also in some terrestrial species Excretion of ammonia End sac is a coelomic cavity and is lined with podocytes Malpighian Tubules Typical for terrestrial arthropods insect and arachnids but saccate nephridia may be present in addition Excrete uric acid or guanine Blind ending tubes between the midgut and hindgut Gas Exchange Small arthropods gas exchange over entire body surface Larger aquatic species gills are modified legs many crustaceans book gills horseshoe crabs Larger terrestrial species tracheae tubular invaginations of the epidermis insects myriapods and others book lungs many arachnids