Superphylum Ecdysozoa: Nematodes and Tardigrades

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Enumerate features of Caenorhabditis elegans that make it a valuable model system for biologists.


It is a true animal with at least rudiments of the physiological systems—feeding, nervous, muscle, and reproductive—found in “higher animals” like mice and humans. It is so small that large numbers can be raised in Petri dishes. It reproduces rapidly. It is transparent so that every cell in the living animal can be seen under the microscope. Before it dies (after 2–3 weeks), it shows signs of aging and thus may provide general clues as to the aging process.

What are the different ways in which nematodes can reproduce?


There are nematodes with separate sexes and hermaphrodites in addition to species that reproduce parthenogentically. The nematode Caenorhabditis elegans has a self-fertilizing hermaphrodite sex and a pure male sex.

Why are tardigrades essential to recolonizing habits following destruction or mass extinction?


Tardigrades are extremely hardy animals that are capable of surviving extreme conditions that kill other species. Following a catastrophic event in the ecosystem, tardigrades are likely to be one of the few surviving species. They can also function as a pioneer species that moves into a vacated habitat. Once the tardigrade population has expanded in the habitat, predators that use tardigrades as a food source are able to return. This pattern continues up the food web until the ecosystem is restored.