Aschelminthes, commonly known as roundworms, are a phylum of animals with long, cylindrical bodies. Unlike flatworms, these creatures have a complete digestive system with a mouth at one end and an anus at the other.

Body Structure and Symmetry

Roundworms show bilateral symmetry, meaning their bodies can be divided into two identical halves if cut down the center. Their body is covered by a tough, resistant cuticle, which is a protective outer layer that prevents digestion by the host. A key feature is the pseudocoelom, a fluid-filled body cavity that is not fully lined by mesoderm tissue. This cavity acts as a hydrostatic skeleton, helping the worm maintain its shape and move.

Habitat and Lifestyle

These worms live in almost every environment on Earth. Many are free-living in soil or water, feeding on bacteria and decaying matter. However, many species are parasitic, meaning they live inside other animals or plants to get their food. For example, Ascaris lumbricoides is a famous roundworm that lives in the human intestine. Another example is Wuchereria bancrofti, which causes the disease known as filariasis.

Important Biological Facts

• Separated Sexes: In Aschelminthes, males and females are distinct, meaning they have separate genders.
• Size Variety: They range from microscopic sizes to some species that can grow over 1 meter long.
• Sexual Dimorphism: Often, males are smaller than females, and males possess a curved tail tip.
• Internal Fertilization: They reproduce sexually, and fertilization occurs inside the body of the female.