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McGill University
Biology (Sci)
BIOL 111

Bio 111 Alanna Houston November 1, 2007 ARTHROPODS - grouped based on head parts: chelicerates and mandibulates - mandibulates: hexapods, crustaceans, myriapods - Hexapods: - Body regions: head (antennae, mandibles), thorax (3 pairs of walking legs…may have wings), abdomen (no appendages) - Insects - Stalk-eyed flies (eyes off appendages)- male with widest eyes gets to reproduce with the female (sexual selection) - Wings evolved 320 mya: o Secondarily lost over time by some insects Insects: - Most abundant and diverse group o Herbivores, detritivores, fluid-drinkers, predators, scavengers, parasites o 1/3 are beetles o flies, fleas, bees, termites, aphids… o leaf-cutter ants feed the fungus that eats the leaves o ants sitting on the leaves are individuals protecting the workers. Protecting them from wasp eggs being laid in their abdomen (eggs with hatch and burst out of the ant killing it. o Insects are the most successful group because they voevolved with angiosperms (pollination), they evolved flight, they were the first to invade land, they evolved flight Metamorphosis: - Molting enables changes in morphology = metamorphosis o Each instar (larva) produces a new exoskeleton Bio 111 Alanna Houston o At each molt, modification is possible - Insects cease molting as adults. - Metamorphose to adult form: o Incomplete metamorphosis or complete metamorphosis - Crustaceans continue molting as adults - Complete: o Abrupt changes in form  Juveniles do not resemble adults  Resting stage (pupa) o Often major habitat changes o Dragonflies o - Incomplete: o Gradual changes in form  Juveniles similar to adults  No resting stage o No habitat change Crustaceans: - largely marine - head and thorax (cephalothorax) and abdomen - appendages off each segment - compose ‘zooplankton’ - crabs, daphnia, barnacles, shrimp, crayfish, isopods… - Parasitic isopod (eats tongue of host and then acts as a tongue Myriapods: - 2 regions: head and trunk - Centipedes (Chilopoda) o One pair per segment o Carnivores - Millipedes (Diplopoda) o Two pairs per segment o Detritivores, Herbivores Chelicerates: - arachnids (spiders, mites, scorpions) - horseshoe crabs - no jaws (mandibles) - 2 body regions: o cephalothorax (appendages) Bio 111 Alanna Houston o abdomen – no appendages - appendages: o #1 (chelicerae) fangs o #2 (pedipalps) copulatory organs, pincers o #4,5,6,7 walking legs - Chiggers: nymph (larva of a mite). Live on trees and develop into trees. Sense heat of warm-blooded mammals and drop off onto host to attach to skin and release enzymes. Feeds on liquefied tissue etc. Arthropod circulatory system: - open system - dorsal tubular heart (1 chamber) with pores (ostia); drives blood into hemocoel spaces - one way valves Respiratory System: - crustaceans: gills - Insects: o Holes (spiracles) open into tubular tracheae which branch into finer tubes o Carry O2 to body cells o Required because of exoskeleton Regulation of Molting: - wigglesworth’s experiments using Rhodnius prolixus o a blood-sucking insect, molts after blood meal o it can live for long time after it is decapitated - Molting experiment 1: o Some substance diffusing from the head of rhidnius prolixus
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