Question

Nematoda: Unsegmented round worms, longitudinal muscle and distinctive form of locomotion, alimentary canal. How can these survive without circulatory or gas exchange systems? How does this concept relate to their size, shape, and habitat?

Define how the terms are related to Nemotoda, and answer the question succinctly, but fully.

Answer 1

Phylum Nematoda consists of round worms which are unsegmented worms. These worms live in variety of habitats such as moist soils, fresh and saltwater ecosystems. These occur as free living or as parasites. Most of them are decomposers and have a significant role in nutrient cycling. Many of them are herbivores, some are carnivores and parasites.

These have small and slender bodies tappered at the both the ends. They have bilateral symmetry but the head is radially symmetric. The body of worms is enclosed in a cuticle and hypodermis under it. Cuticle is rigid and maintains the shape of worms as cylindrical. The cuticle enables stetching and bending. It also allows the entry of gases and water. The cuticle is molted during growth of worms. The worms are composed of longitudinal muscles that contract and enable the thrashing movement. The body contains the fluid filled pseudocoelom and it transports the nutrients through the fluids. The worms contain alimentary canal and no circulatory system. Thus, transport process is accomplished by fluid flowing through pseudocoelom.

Since, the circulatory and gas exchange systems are absent most of them are parasited that absorb nutrients through cuticle and exchange gases through cuticle. Same can happen with decomposers and therefore, most of them live in moist habitats that enable them to absorb nutrients through body surface.