Department of Zoology at ANDC/Zoology Museum/Museum specimens/Nemathelminthes

{|cellpadding="5" cellspacing="5" style="width:100%;background:#CCCCFF; border-style:solid; border-width:3px; border-color:#013220;" {|width="100%" cellpadding="2" cellspacing="5" style="vertical-align:top;background-color:#66CDAA" !  Phylum Nemathelminthes
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{|cellpadding="5" cellspacing="6" style="width:100%;background:#FFFFFF; border-style:solid; border-width:3px; border-color:#0066FF;" Date & Time : 28, August 2024      
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= General Characteristics of Nemathelminthes =

• Phylum Nemathelminthes comprises of animals commonly called nematodes or roundworms.

• Nematodes are ubiquitous and are found in freshwater, marine, as well as terrestrial environments.

• Most of the species of nematodes live a parasitic life, though a number of free-living forms are also present.

• These are triploblastic, bilaterally symmetrical animals with organs system level of body organization.

• Body is elongated, cylindrical, unsegmented and vermiform.

• Size of the nematodes varies considerably in different species.

• Body is covered by a resistant, inelastic and thick cuticle which is covered by a thin and lipoid epicuticle.

• Epidermis is syncytial in nature and is invaginated into four longitudinal cords.

• Body wall has thick muscle layer composed of only longitudinal muscles which are present between four cords.

• The body cavity is a pseudocoel and is not lined by coelomic epithelium. It contains pseudocoelomic fliuid rich in proteins, and organic metabolites.

• Nematodes exhibit undulating movement in dorso-ventral plane produced by alternate contraction and expansion of the longitudinal muscles.

• Circulatory and respiratory system are absent.

• Digestive tract is straight and complete with two openings, mouth and anus.

• Flame cells are absent and excretory system consists of a few renette cells or a canal system.

• Nervous system comprises of a circum-pharyngeal nerve ring surrounding the pharynx and four peripheral longitudinal nerves.

• Sense organs are poorly developed and include amphids, phasmids, papillae, bristles and ocelli.

• Sexes are separate with distinct sexual dimorphism.

• Gonads are unpaired or paired and are tubular or coiled.

• Sexual reproduction is the common form of reproduction.

• Fertilized eggs are surrounded by a tough capsule.

• Cleavage is determinate and development includes usually four larval stages.

• Development of embryo takes place with or without intermediate hosts.

=Classification of Nemathelminthes=

Phylum Nemathelminthes is divided into two classes based on the presence or absence of phasmids.

a) Adenophorea or Aphasmidia

• Phasmids, the sensory organs in the caudal end, are absent.

• Amphids, the chemoreceptors are variably-shaped and are present behind the lips.

• Excretory canals are absent.

• Most species are free living and some are parasitic.

• Free living species include almost all marine forms; and some terrestrial and freshwater forms.

A few examples are Xiphinema, Mermis and Enoplus.

b) Secerenentea or Phasmidia

• Phasmids are present which open through minute pore on each side near tip of tail.

• Amphids are pore-like and are present in the lateral lips.

• Excretory canals are present.

• Most of the species are parasitic in nature.

• Free living species are soil inhabitants.

A few examples are Ascaris, Wuchereria, Oxyuris, Ancylostoma and Dracunculus

= A Few Examples =

1. Ascaris lumbricoides 

2. /Ancylostoma duodenale/

3.''/Wuchereria bancrofti/