Nematoda
Physical Structure
Nematodes, most commonly referred to as roundworms, have the most diverse in a phylum of invertebrate animal with a three layered body. It is also one of the most diverse of all animals. There have been over 28,000 have been described, 16,000 or more of which are parasitic. This makes them very hard to distinguish. There have been estimations that total number of nematode species are about 1,000,000. Roundworms have tubular digestive systems with openings at both ends. Unlike cnidarians or flatworms who have one opening. They are typically less than 2.5mm long and some are even microscopic, which explains why they make up a lot of the specie population but we cannot notice them. Their bodies are bilaterally symmetrical, but their heads are not. They also only have one recognized class which is the secernentea
Here are the intestines of a nematode |
Where do I find them?
They can be found in nearly every ecosystem because they have so much variation that allow nematodes to live in different places. They can be found in freshwater, salt water, or on land were they usually outnumber the amount of animals there (both by species and individually). They can even be found in deserts, ocean trenches, mountains, and even inside the Earth. In an ecosystem they usually make up 80%-90% of the specie there. If things get a bit to extreme to handle then the nematodes can go into cryptobiosis. In this state the worm suspends its life processes and can withstand extreme drying, heat, or cold and it can return to normal back whenever it feels that the environment is suitable.
Muscular System
They have muscles underneath their epidermis that allows them to move side-to-side. They cannot not lifts themselves to they have to crawl everywhere.
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This video shows that it cannot lift itself and looks like it is thrashing when it wants to move.
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Credit goes to Daraxzaraz for filming the nematoda.