Helminthology, Biology tutorial


Helminthology is the study of parasitic worms (that is, helminths), whereas helminthiasis explains the medical condition of being infected by helminths. Helminthology deals with the study of the taxonomy of helminths and the consequence on their hosts.

The word helminths has been derived from the Greek word which means worn. It was originally meant to refer to only intestinal worms, however now comprise tissue parasites and also numerous free living species. These are Metazoa.

General features of helminths:

1) They don't possess organs of locomotion; therefore locomotion is through muscular contraction and relaxation.

2) The outer covering, termed as cuticle or integument. It is positioned on its outer surface and might be armed having hooks or spines. It is resistant to intestinal digestion.

3) Excretory system and Nervous system are primitive.

4) Digestive system is complete, partly lost (that is, rudimentary) or absent. The alimentary area has completely disappeared from all phases of the tapeworms (that is, cestodes); it is greatly or almost absent in most of the Trematodes, however is present and complete in most of the nematodes. The digestive system is partly lost (that is, rudimentary) or absent in specific parasitic helminths because of their place in the hosts (tissue or intestine), where predigested nutrient are rich.

5) Reproductive system is extremely well developed.

6) They might be monocious or diecious. Both self-fertilization and cross-fertilization might occur.

7) Reproduction to raise the parasite population in the similar host (that is, internal autoinfection) doesn't take place among certain helminths; more over under general conditions of host and environment, the number of worms which reach maturity in any given host is limited levels that are tolerable to both host and parasite. Therefore most of the people who are infected by helminths are asymptomatic carriers and the diseased individuals among the infected group are such having the heaviest worm burdens.

8) If worms are crowded the collective egg output is great, however the output per worm is relatively low, based on the degree of crowding.

9) The factors which find out helminths population are such related with the host-parasite relationship (that is, the immune factors derived from the host responses and the complicated role of co-existing infection)

10) The co-existence of some species of helminths in the similar individual (that is, poly-helminths) is broadly prevalent.

Classification of helminths:

The Metazoa are categorized into two phyla: Platyhelminthes and Nemathelminthes. Platyhelminthesis categorized into two groups: Cestodea (tapeworms) and Trematodea (flukes) while Nemathelminthes consists of only one group Nematodea (roundworms).


Nematodes (roundworms) include long thin unsegmented tube-like bodies having anterior mouths and longitudinal digestive tracts. They encompass a fluid-filled internal body cavity (that is, pseudocoelum) that acts as the hydrostatic skeleton giving rigidity. Worms make use of longitudinal muscles to give a sideways thrashing motion. Adult worms make separate sexes by means of well-developed reproductive systems.


Cestodes (tapeworms) include long flat ribbon-like bodies having a single anterior holdfast organ (that is, scolex) and many segments. They don't have a gut and all nutrients are taken up via the tegument. They don't encompass a body cavity (that is, acoelomate) and are flattened to facilitate perfusion to the entire tissues. Segments show slow body flexion generated by longitudinal and transverse muscles. Each and every tapeworm is hermaphroditic and each segment includes both female and male organs.


Trematodes (flukes) include small flat leaf-like bodies having oral and ventral suckers and a blind sac-like gut. They don't encompass a body cavity (that is, acoelomate) and are dorsoventrally flattened by bilateral symmetry. They show elaborate gliding or creeping motion over substrates by using compact 3-D arrays of muscles. Most of the species are hermaphroditic (individuals having female and male reproductive systems) however some blood flukes form separate female and male adults.

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