Phylum Aschelminthes - Practice Questions & MCQ

• Aschelminthes are also called Nemathelminthes or Nematodes.
• These are known as ‘roundworms’ as the cross-section of the body appears circular.
• These are triploblastic and pseudocoelomate animals. It implies that there is pseudocoelomic fluid that acts to provide hydroskeleton.
• These can be parasitic or free-living.
• They show organ system level of organization
• Ascaris (Roundworm), Wuchereria (Filaria worm), Ancylostoma (Hookworm) are the examples

Body Plan of Aschelminthes:

• The epidermis is surrounded by a thick cuticle.
• It is followed by a muscular layer.
• Between the muscular layer and gut, the pseudocoelom is present which is filled with fluid.
• The digestive tract is surrounded by gastrodermis that forms the innermost layer of the body.
• They show a tube-within-tube type of body plan.
• They have an unsegmented body.
• The body shows tapering ends at both extremities.

Digestion in Aschelminthes

The digestive system is complete with a distinct mouth and anus. Therefore, they have a tube-within-tube type of body plan. Digestion is extracellular. Stomach is absent.

Excretion in Aschelminthes:

• The excretory system is not well developed in nematodes.
• The nitrogenous wastes are removed through the process of diffusion via the excretory pores.
• In marine forms, the rennette glands are present below the pharynx that helps in osmoregulation.

Nervous System

• The nervous system comprises a nerve ring and nerve chords extending from it.

• Aschelminthes are dioecious animals, i.e., the male and female reproductive organs are present in different individuals. 
• Sexual dimorphism is also observed, i.e., females are longer than the males. 
• Fertilization is internal
• Development is indirect or direct

The following types of larvae are seen in different roundworms:

• Filariform larva - hookworm
• Microfilaria larva - Wuchereria
• Rhabditiform larva - Ascaris