🧖🏽‍♀️ Morphology

👉🏻 The outer body tube or body wall comprises of three layers:

• Outermost Layer: Cuticle
• Middle Layer: Hypodermis
• Innermost Layer: Somatic Longitudinal Muscles

  

Cuticle

• The cuticle is a non-living, non-cellular, triple–layers covering that is secreted by the underlying hypodermis.
• The cuticle is flexible. It covers the entire body and lines the oesophagus, vulva, anus, cloaca, excretory pore and sensory organs.
• The feeding stylet and copulatory spicules are formed from cuticle. The external lining is known as exo-cuticle and internal linning is known as endo-cuticle.
• The composition and from of the cuticle is highly variable. In general, the cuticle is composed of three primary zones viz.,
  • Cortical Layer
  • Median Layer
  • Basal Layer
• The cuticle of may nematodes have markings on the surface. They are varied and complex and have been often used by taxonomists to assist in the identification of various species.
• The cuticular markings are categorized into different types:
  • Punctuation
  • Transverse marking or Striations
  • Longitudinal markings

Function

• Cuticle along with hypodermis forms the exoskeleton of nematodes which provides a proper shape to the nematode body in conjunction with pseudocoelom.
• This body wall protects the nematode from the harsh external environment, serves as the exoskeleton and provides the mechanism for movement of the organism through the soil and plant tissue.
• The body wall also contains much of the nervous and secretory – excretory systems, and it plays a role in the exchange of gases.
• It regulated permeability as the cuticle acts as a semipermeable membrane allowing entry of water and non-electrolytes but preventing entry of any undesirable elements.
• It responds to stimuli from the external environments through sensory structures associated with the surface of the cuticle.
• It also helps growth of the nematode body because of moulting. Nematodes on their development from J₁ to adult, undergo four moults and in each moult, both exo and endocuticles are replaced by the new cuticle secreted from the hypodermis in a process called Ecdysis.

Caudal Alae

• A pair of lateral wing like cuticular expansion around the tail of the male nematode is called caudal alae.
• It is commonly called Bursa.
• It helps male nematode to grasp and clasp the female during mating.

Amphid

• A pair of lateral chemo-sensory structure present on the surface of cuticle at the lateral lips located exactly opposite to each other.
• Amphids are the chemoreceptor structure which can detect any chemical changes on the outermost environment helping plant parasitic nematode to recognise the favourable host plant for feeding.

  

Phasmids

• Phasmids are pair of lateral chemo-sensory structure appearing as pore-like openings located in the mid tail region exactly opposite to each other.
• These are chemoreceptors structure which act on scent trail attracting members of the same species to assemble together at the site of feeding.

Deirids

• A pair of lateral outgrowths on the centre of lateral field at the level just below the nerve ring on the surface of cuticle are deirids.
• Located exactly opposite to each other.
• They are mechanoreceptor structure determining the size of the pore space prior to entry of the nematode through the pore space.

Hypodermis

• Hypodermis is single live cellular layer.
• It is metabolically very active layer helping secretion and maintenance of the cuticle.
• It induces moulting helping formation of new cuticle from hypodermis by secretion of leucine amino peptidase enzymes.
• It acts as osmotic and ionic regulator.
• Act of energy reservoir part helping the nematode during starvation.

Somatic Longitudinal Muscles

• The innermost lining of body wall is somatic longitudinal muscles which are arranged in rows at the base of the hypodermis.
• Muscle cells are rich in glycogen that helps the nematode to utilize the stored glycogen during starvation.
• It helps in movement of nematodes.

- Walia, R. K and Bajaj, H. K (2014). Textbook of Introductory Plant Nematology. Directorate of Knowledge Management in Agriculture, ICAR, New Delhi. 
- Ravichandra, N. G. (2019). Plant Nematology. I. K. International Publishing House Pvt. Ltd., New Delhi. 
- Dasgupta, M. K. (1998). Phytonematology. Pilgrims Publishing 
- Fotedar, D.N. & Handoo, Z.A. (1978) A revised scheme of classification to order Tylenchida Thorne, 1949 (Nematoda). Journal of Science, University of Kashmir (1975), 3, 55–82. 
- Qing, X., Bert, W. Family Tylenchidae (Nematoda): an overview and perspectives. Org Divers Evol 19, 391–408 (2019). 
- https://doi.org/10.1007/s13127-019-00404-4 
- https://nematode.unl.edu/dolichod.htm 
- http://www.nematologia.com.br/files/tematicos/6.pdf