BIOL1002 Lecture Notes - Lecture 6: Hydrostatic Skeleton, Circulatory System, Arthropod
6 Nov 2018
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Include the arthropods and grow intermittently by shedding an exoskeleton. The ecdysozoans are comprised of 7 phyla, the most prominent of which are the nematoda (roundworms) and arthropoda (arthropods). All ecdysozoans grow by shedding (moulting) an external body covering (cuticle, or exoskeleton if it is hard). This mode of growth is a synapomorphy for ecdysozoans. Advantages of a stiff body covering include protection and provides structure for muscle attachment. There is a lot of variation in thickness and weight of these coverings. Arthropods (particularly insects) are the most abundant animals in both terrestrial and marine environments, and make up about 80% of all known animal species. Arthropods include the myriapods (millipedes and centipedes), insects, crustaceans (crabs, lobsters, etc), and chelicerata (such as spiders). Possessi(cid:374)g a rigid e(cid:454)oskeleto(cid:374) (cid:373)ea(cid:374)s that arthropods do(cid:374)(cid:859)t (cid:374)eed to rel(cid:455) o(cid:374) a hydrostatic skeleton for movement: most arthropod movement is based on muscles applying force against the exoskeleton to move legs or wings.
