Roundworms are mostly microscopic and free living, but the ones we humans talk about the most are the parasites that infect our pets and even our own bodies. They were the first animals to exhibit a coelom, or a fluid filled cavity where their organs are kept. They were also the first animals with two openings in their endoderm, making a gastrovascular tract.
Body Cavity
Unlike flatworms, roundworms have a "false" coelom between their mesoderm and ectoderm. This development allowed them to circulate materials throughout their bodies through simple gas exchange between the coelom fluid and their organs. Roundworms are also typically very small because they do not have a more advanced circulatory system.
Unlike flatworms, roundworms have a "false" coelom between their mesoderm and ectoderm. This development allowed them to circulate materials throughout their bodies through simple gas exchange between the coelom fluid and their organs. Roundworms are also typically very small because they do not have a more advanced circulatory system.
Body Plan
Like flatworms, roundworms exhibit cephalization. They have a nerve ring near the anterior of their body. They also have two nerve cords running down the length of their bodies. Round worms have a mouth and an anus, so digestion is able to take place in the gut from entering the mouth to leaving the anus. Roundworms can be male or female. Females will lay eggs outside their bodies where males can then fertilize them, so this is external fertilization.
Like flatworms, roundworms exhibit cephalization. They have a nerve ring near the anterior of their body. They also have two nerve cords running down the length of their bodies. Round worms have a mouth and an anus, so digestion is able to take place in the gut from entering the mouth to leaving the anus. Roundworms can be male or female. Females will lay eggs outside their bodies where males can then fertilize them, so this is external fertilization.
Lifestyle
Most roundworms are free living but the ones that are parasitic tend to have a life cycle similar to the one in the video below.
Most roundworms are free living but the ones that are parasitic tend to have a life cycle similar to the one in the video below.