Question

22. Mention the general characteristics of the nematodes.

23. Describe the anatomy of the body wall in nematodes.

24. Describe the anatomy of the digestive system. Explain how food digestion occurs.

25. What is the function of the pseudocelloma fluid?

Answer 1

Answer 22 :

The general characteristics of the nematodes are :

• Phylum Nemathelminthes (Aschelminthes) includes roundworms or nematodes.
• Nematodes are found everywhere. They may be free-living - aquatic or terrestrial.
• They may be parasites in plants and animals.
• They have a long cylindrical body with tapering ends which appear round or circular in cross-section (hence, they are called roundworms).
• The body is without segmentation.
• They show bilateral symmetry
• Their body is triploblastic - formed from 3 germinal layers - ectoderm, mesoderm and endoderm.
• They have an organ system level of organization.
• Body plan is called tube within the tube  
• The anterior end does not show distinct head i.e.. cephalization is absent.

Answer 23 :

The body wall of nematodes consists of :

1. Cuticle - This is the outermost layer that is non -living , thick and resistant to digestive enzymes of host.   
2. Epidermis - This middle layer is Syncytial i.e.. a continuous layer of cytoplasm with scattered nuclei.
3. Muscle Layer - This innermost layer has only longitudinal muscle fibers

Answer 24 :

Digestive system and digestion in nematodes :

• The digestive tract in nematodes is complete.
• Their digestive system is divided into three parts namely stomodeum, intestine and proctodeum.
• The stomodeum consists of the mouth, esophagus and pharynx.
• The pharynx is muscular and well developed and is used to suck the liquid food inside.
• When food is ingested from the mouth, it travels into the oesophagus and the pharynx. The esophagus pumps the food down into the tube-like intestine.
• Intestine is non-muscular and food just passes through to the cloaca in males and the rectum in females.
• The food is digested, the minerals are absorbed and the waste is excreted out through the annus.

Answer 25 :

Round worms are pseudocoelomate. Pseudocoel is when body cavity is there between the body wall and the digestive tract but is not lined by mesodermal epithelium. The fluid present in the pseudocoel is important for the following functions :

• It maintains the turgor-hydrostatic pressure in the animal
• It functions as a lubricant between the tissues of the animal
• It also provides a medium for transport of nutrients
• It helps in intercellular signaling.