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Arthropods I and II
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Lecture notes on arthropods (part of bilaterians, molluscs and arthropods)
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Lecture 4: ArthropodsEcdysozoans have a 3 layered cuticle, molted as the animal grows (ecdysis). Arthropods are found in
this group. Arthropods are sister groups to Lobopodia. Arthropods are the most successful group in
terms of species numbers, ecologically and geographically.
Ecdysozoans have a hard, 3 layered cuticle made of chitin. Also found in radula of molluscs and
beaks of cephalopods. It's very hard when cross linked with proteins. It's molted for the organism to
grow.
The cuticle is made of 3 layers:
Epicuticle - water resistant layer of protein, lipoprotein, lipid and sometimes wax.
Exocuticle - scleritised where it needs to be hard, left flexible in other areas. Made of chitin and
protein.
Endocuticle - mostly chitin, often mineralised with calcium
They have chaetae which provides attachment and sensory functions (not same as cilia).
The hormone called ecdysone causes the animal to go through its molt.
The ecdysial line allows the animal to predict what part of the body is going to break open when it
molts. Ecdysozoa are vulnerable during molting because its soft. Cuticle is hardened during
scleritisation. Each molting is called an instar.
Differences between arthropods and humans:
Arthropods develop backwards
Upside down body plan
Has an exoskeleton instead of an endoskeleton.
Key features of arthropods
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