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TAMU MARB 435 - Arthropoda
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Marb 435 1st Edition Lecture 17 Current Lecture: Arthropoda 1Phylum Tardigrade About 800 species Generally only 100-150 μm, 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 hoursPHulum 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 papillaeThese 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 GangliaFeeding 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 cuticlePhylum 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 hemocoelEvolutionary success story:• One out of three animal taxa with powered flight• The most successful colonizers of terrestrial habitatsTagmosis Tendency to organize segments into regions with similar structure, function and appendages Basic tagmata:head, Thorax and abdomenExoskeleton 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 uptakeEcdysis (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 shedMuscular and nervous systemo 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 inhibitoryo 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 contractionAppendages 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 musclesBody 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 hemocoelExcretionSaccate NephridiaTypical for aquatic arthropods, but also in some terrestrial speciesExcretion of ammoniaEnd sac is a coelomic cavity and is lined with podocytesMalpighian TubulesTypical for terrestrial arthropods (insect and arachnids), but saccate nephridia may be present inadditionExcrete uric acid or guanineBlind ending tubes between the midgut and hindgutGas 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


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