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Earthworm Vs Annelida

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ife began on earth about 3.5 to 4 billion years ago, since then it has evolved and flourished. Within the kingdom Animalia, it alone consists of 35 phyla. Two of which are Onychophora and Annelida. Onychophora are believed to be a possible link between two phylums of Annelids and Arthropods as it carries characteristics of both groups. This essay seeks to compare and contrast between the earthworms from phylum Annelida and the velvet worms from phylum Onychophora.
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Velvet worms and earthworms are superficially similar animals.
Both have a bilateral symmetry and an organ system level of body organisation. With regards to their tissue development, both are triploblastic animals with three tissues layers. These layers are the endoderm, …show more content…
Due to their lack of gills or lungs, gaseous exchange with the environment is done through their body surfaces. Oxygen is able to reach different parts of their body through blood vessels. Earth worms have five of such blood vessels on each side in place of a heart. These blood vessels can be enlarged and muscular at the anterior ends of the earthworm in order to help pump the blood (Raven, Johnson, Losos, Mason, singer, 2008). Unlike earthworms, velvet worms have an open circulatory system. Though it lacks capillaries, it has a hemocoel and a dorsal heart with ostsia (Margulis, Chapman, 2009) Thus their blood flows through cavities and not through closed blood vessels. Another notable difference can be seen from their respiratory systems. As stated earlier, earthworms undergo gaseous exchange through their skin. This is done through a process called diffusion. Body fluids are secreted to keep the skin moist for diffusion to occur. For velvet worms however, their respiratory system consists of small, branched air-ducts called tracheae. These tracheae will proliferate to the rest of its body to transmit oxygen to all parts. Velvet worms have specialised openings called spiracles which allows air to pass into the tracheae (Raven, Johnson, Losos, Mason, singer,

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