Anatomy and Morphology

 

 

Contents

Rev. 12/04/12
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  Dictionary of Terminology  

Digestive System

Three parts:  

(i) Stomodeum:

Consists of:

Lips - hexaradiate - usually six, reduced to 3 in Ascarids, 2 in Spirurida.  Lips may be extended into probolae and other ornamentation, - e.g. Cephaloboidea - Cephalobus.

Stoma - buccal cavity - movable and immovable armament common in all Nematoda - teeth, etc.

Globose buccal cavity

 

Occurs in some predaceous nematodes

Collapsed or funnel-shaped stoma ( buccal cavity):  

Order Rhabditida, Suborder Tylenchina

Bacterivores, e.g. Cephalobus

 

Tubular stoma (buccal cavity):  

Order Rhabditida, Suborder Rhabditina

Bacterivores, e.g. Rhabditis

Protrusible spears in 2 orders:  Tylenchina and Dorylaimida

 

Tylenchida:

  • stomatostyle is protrusible

  • it has an anterior conical portion (with subterminal ventral opening), shaft, knobs.

  • cone is shed, shaft and knobs are  resorbed at molt.

  • cone of stomatostyle from anterior of stoma - embryological origin is the cheilostome. 

  • shaft, knobs are esophageal, from the esophastome.

  • stomatostyle often distinguished by referring to it as the stylet.

(From Baldwin and Hirschmann (1971) as modified by Maggenti (1981))

Dorylaimida:

  • odontostyle is the protrusible hollow spear.  It appears to form in a cell that is esophageal in position, but that cell is one that has probably migrated from the stoma region.
  • odontophore is a cuticular extension of the spear that is esophageal in origin - from the esophastome.
  • odontostyle often distinguished by referring to it as the spear.

 

Triplonchida:


onchiostyle is the grooved solid tooth or onchium and its extension, the onchiophore.
the term spear is often used for the onchiostyle.

Spear is axial and is contiguous with odontophore

e.g. Dorylaimus

Spear is a mural tooth, not contiguous with odontophore

e.g. Nygolaimus

 

 

Curved, solid tooth (onchium) and onchiophore, with dorsal groove,

e.g. Trichodorus

Esophagus - a variety of forms in different Orders - 2-part, 3-part. 

 
  • Basic structure is corpus, usually muscular (anterior), and postcorpus, with glands (posterior).

Order Enoplida Order Dorylaimida Order Rhabditida Order Tylenchida
From Maggenti (1981)

Stylet, esophageal lumen and metacorpus pump of a tylenchid nematode. (From Sforza and Eisenback, 2001). Cross-section of metacorpus with radial muscles relaxed and pump chamber closed. Cross-section of metacorpus with radial muscles contracted and pump chamber open.
Longitudinal section of metacorpus of a tylenchid nematode. (Adapted from Wyss, 2002).

 

Posterior part of the esophagus, consisting of the isthmus and postcorpus bulb.

In the order Tylenchida (which contains many plant feeders) the esophageal glands are surrounded by membrane.  The relationship of the esophageal glands of the postcorpus and the intestine (overlap or abutting) can be diagnostic.  The dorsal esophageal gland is ducted to the anterior and opens (dorsal esophageal gland opening - DEGO) into the esophageal lumen behind the stylet (suborder Tylenchina) or into the metacorpus (suborder Aphelenchina).  ((Maggenti, 1981; Ferris).

In the order Rhabditida, besides containing the esophageal glands, the postcorpus is also the main pumping structure for ingestion of food.  Cuticular plates lining the edges of wall evaginations of the pump chamber suggest a grinding or maceration function and have led to this structure being termed the grinder.

Generalized structure of the postcorpus and postcorpus pump in the order Rhabditida (Modified from Zhang and Baldwin, 2001).
Cardia of Tripyla tropica

from Cid et al., 2010

 

 

(ii) Mesenteron:

  • Simple tubular intestine, surrounded by single layer of endodermal epithelium.
  • Microvilli on inner lining.

 

 

(iii) Proctodeum:

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