Biology 3484A/B Lecture Notes - Cambrian Explosion, Hemocyanin, Sea Anemone
24 Dec 2012
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The phylum arthropoda includes crabs, lobsters, shrimps, spiders, ticks, mites, scorpions, horseshoe crabs, millipedes, and centipedes. They have a segmented body with segments grouped into functional units. They have jointed appendages and many pairs of jointed limbs. They undergo metamorphosis with different stages egg, immature (nymph/larva), adult. They are the most diverse group of organisms on the planet. Exoskeleton: is an external skeleton and is the entire outer surface of the animal. It is formed of chitin (a structural polysaccharide) and sclerotin (proteins in a matrix). The exoskeleton is continuous, but segmented hard rigid plates are connected by softer, flexible material (joints). It is periodically shed and renewed as the animal grows (metamorphosis). Metamorphosis in arthropods is a change in form during postembryonic development and growth. When an animal outgrows the current exoskeleton, first the new one forms underneath the existing exoskeleton. Then molting occurs a process of shedding the old outer exoskeleton.
