Anatomy and Morphology

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	Dictionary of Terminology

Digestive System

Three parts:

Stomodeum - stoma + esophagus (ectoderm + mesoderm (muscle))
Mesenteron - intestine (embryologically endoderm)
Proctodeum - rectum, anus (ectoderm, cuticle lining).

(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

Stomatostyle in Tylenchina
Odontostyle, odontophore in Dorylaimida
Onchiostyle is used for the feeding structure of Trichodoridae

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)

Dorylaimid Esophagi configurations

Transition between anterior and posterior regions of dorylaimid esophagi:

Pena-Santiago, R. 2006. Dorylaimida Part 1. Superfamilies Belondiroidea, Nygolaimoidea and Tylencholaimoidea. Pp 326-391 in E. Abebe, István Andrássy, W. Traunspurger (eds) Freshwater Nematodes: Ecology and Taxonomy. CABI Publishing.

Some dorylaimid esophago-intestinal cardia configurations

Corpus may be further differentiated into procorpus and metacorpus.
Metacorpus is muscular and may have a valved pump.


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).

Postcorpus

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

Isthmus is a narrower region between metacorpus and postcorpus - surrounded by nerve ring with nerve continuity into dorsal and ventral hypodermal chords.
Postcorpus bulb is the enlarged base of the esophagus which contains the esophageal glands and may contain a pumping apparatus.

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 or Cardiac Valve is a muscular structure at the base of the esophagus at the opening into the intestine.
Cardiac Glands are three glandular bodies located at the base of the esophagus in certain taxa.

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:

Rectum is the short portion of the digestive tract at the end of the intestine. It opens to anus in female, cloaca in male.
Cloaca is common opening of reproductive and digestive system in male; reproductive system in female opens through the vulva, which is separate from the anus.
Cloaca, anus and rectum are lined with cuticle.

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