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Exam 3 notes - Phylum Arthropoda Similarities between...

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Phylum Arthropoda Similarities between Arthropods and Annelids o Body metamerism o Embryonic development o Architecture of nervous system Differences between Arthropods and Annelids o Rigid exoskeleton in arthropods Led to open hemocoel and jointed appendages Bauplan and Arthropodization Hard, jointed exoskeleton o Distinguishes from annelids o Protection helped lead to success Cuticle: provides barrier against osmotic and ionic gradients (homeostatic control) Regional Specialization: tagmosis- specialized body regions (tagmata); mediated by Hox genes Arthropodization o Solved problems related to adding jointed exoskeleton to annelid-like form (growth and locomotion) Locomotion and Circulation: all mobile body cilia lost so body and appendage joints and regionalized muscles added; flexibility by joints in exoskeleton w/ elastic protein resilin; lost circular muscles so no peristaltic movt => coelom useless and lost => open circulatory syst w/ body cavity being hemocoel (annelid-like dorsal vessel retained to keep blood moving and became muscular => heart) Excretion: excretory organs became closed internally => blood can’t drain from body Growth: ecdysis (molting- 1 st appeared in Onychophora) Body Wall Epidermis called hypodermis Each body segment called somite o Have skeletal plates called sclerites Each has large dorsal and ventral sclerite called tergite and sternite Sides called pleura o Flexible, no sclerites o Legs and wings originate here Cuticle o Outer layer: Epicuticle Critical to invasion of land and fw External surface: protective lipoprotein layer (cement layer) Below is waxy layer: barrier to water loss
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o Middle layer: Procuticle Layers of protein and chitin Outer exocuticle and inner endocuticle o Innermost layer: Cuticulin layer Proteins, involved in hardening of exoskeleton Has canals for wax to reach waxy layer 2 parts: thin, dense outer layer and thick less dense inner layer o Sclerotization Hardening of cuticle Arthropod Appendages Have sets of extrinsic muscles (connect limbs to body) and intrinsic muscles (in limb) Podites: Limb segments o 2 groups o basalmost = protopod Basalmost always called coza Can give off addit’l structures Laterally: exites o Ex. biramous limbs: Gills, gill cleaners called epipods; swimming paddles Biramous occur only in crust. and trilo. *Uniramous for walking* Medially: endites o Form grinding surfaces: gnathobases o distalmost = telopod Telopod arises from distalmost protopodal article o Protopods Support and Locomotion Exoskeleton for support and maintenance of body shape Muscles short bands, extend from one body segment to next or across joints of appendages Cuticle thin where lots of movt o Called arthrodial or articular membranes o Each has 1+ pairs of antagonistic muscles (flexors and extensors) o Only allow movt in one plane Contact points that border articular membrane called condyles Swimming o
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