BIO 469 Lecture Notes - Lecture 15: Ventral Nerve Cord, Arthropod Cuticle, Arthropod Leg
13 Jun 2018
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Phylum Arthropoda
● Triploblastic, bilateral
● Hard exoskeleton
● Specialization of appendages
● Jointed appendages
● Coelom that acts as an open circulatory system (heomocoel)
● Excretory and gas exchange organs
● Sense organs that extend out of cuticle
● Growth through molting (ecdysis)
● Cuticle
○ Secreted by epidermis
○ Setae for sensing
○ Pointy structures part of cuticle, not used for sensory purposes
○ Waxes, lipoproteins, proteins
○ Sclerotized - tanning process that hardens
○ Many different structures within
● Support
○ Each segment bound by four plates - dorsal tergite, ventral sternite, and two
lateral pleurites.
○ Muscle bands attach to apodemes (ridges, ingrowths from exoskeleton)
○ Appendages segmented with extrinsic or intrinsic muscles
■ Uniramous or biramous
■ Parts are specialized for different tasks
○ Joins have thin flexible membrane
○ Antagonistic muscles: flexors and extensors
○ Joints in one plane or ball-and-socket
○ Exoskeleton has condyles that act as fulcrums
● Locomotion
○ Walking involves the the coordinated movement of uniramous appendages in
different planes.
○ Subphylum Myriapoda
■ Millipedes (Class Diplopoda) have two per segment on each side. Slow
but powerful
■ Centipedes (Class Chilopoda) have one leg per segment on each side.
Fast but not as powerful
○ Flapping phyllopodia - tail flexion, crawling
● Nervous System
○ “Brain” is 2-3 ganglia with specific functions
■ 3 goes to antenna
○ Ganglionated ventral nerve cord
○ Sense organs (sensilla) protrude out of cuticle
○ Can be slit in cuticle
○ Membranous drums
○ Chemoreceptors with thin cuticle
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● Vision
○ Simple ocelli
○ Complex lensed ocelli
○ Compound eyes made of ommatidia
● Growth
○ Instars have tissue growth but no increase in external size.
○ Proecdysis - old endocuticle digested by enzymes from epidermis. Begin
secreting new endocuticle
○ Ecdysis- old cuticle splits and animal wiggles out. Body swells with water
○ Postecdysis - cuticle hardens, release water
○ Grow through molting
○ Timing of molting
■ Throughout life - crustaceans
■ Periodically until certain size - copepods
■ During metamorphosis - insects
○ Hemimetabolous - insects hatch looking much like adults. Nymphs gradually
attain adult form
○ Holometabolous - young very different from adults. Pupal stage
metamorphoses into adult
● Feeding and Digestion
○ Complete gut with regional specialization
○ Foregut - food intake, transport, storage, mechanical digestion (jaws, pharynx,
gizzard)
○ Midgut - extracellular digestion, nutrient uptake (cecae, digestive gland,
hepatopancreas)
○ Hindgut - excretion of undigested material, water reabsorption
● Circulation and respiration
○ Open hemocoel as a result of hard exoskeleton and lack of internal
segmentation
○ Muscular heart required since body movements cannot move blood
○ Hemolymph has amebocytes, pigments, and some have clotting factors
○ Respiratory structures depend on habitat
■ Trachea in terrestrial insects
■ Gills in aquatic animals
● Fill Branchia (solid sheet, parallel to each other)
● Tricobranchia( central growth tube, and extensions )
● Denobranchia (extensions highly ramified, increasing surface
■ Arachnid book lung (right side of diagram is book lung
○ Respiratory structures depend on habitat
■ Gills in aquatic animals
■ Placement changes for each group
■
● Osmoregulation and Excretion
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Coelom that acts as an open circulatory system (heomocoel) Sense organs that extend out of cuticle. Pointy structures part of cuticle, not used for sensory purposes. Each segment bound by four plates - dorsal tergite, ventral sternite, and two lateral pleurites. Muscle bands attach to apodemes (ridges, ingrowths from exoskeleton) Appendages segmented with extrinsic or intrinsic muscles. Exoskeleton has condyles that act as fulcrums. Walking involves the the coordinated movement of uniramous appendages in different planes. Millipedes (class diplopoda) have two per segment on each side. Centipedes (class chilopoda) have one leg per segment on each side. Sense organs (sensilla) protrude out of cuticle. Instars have tissue growth but no increase in external size. Proecdysis - old endocuticle digested by enzymes from epidermis. Ecdysis- old cuticle splits and animal wiggles out. Hemimetabolous - insects hatch looking much like adults. Holometabolous - young very different from adults. Foregut - food intake, transport, storage, mechanical digestion (jaws, pharynx, gizzard)
