Anatomy and Morphology

	Contents	Rev. 07/21/20
Return to Phylum Nemata Menu	Cuticle	Reproductive System
	Hypodermis/Epidermis	Sensory System
Go to Nemaplex Main Menu	Muscle Layers	Excretory System
Return to General Nematology Menu	Digestive System

a. Cuticle

Striations, annulations, punctations.
Lateral field, lines.
Caudal alae.
Head ornamentation - probolae.
There are four molts of the cuticle in all nematodes.

Molting of cuticle in Belonolaimus longicaudatus.

Note that stylet cone is shed with cuticle.

Photograph from Society of Nematologists

In Adenophorea all layers are molted, in Secernentea epicuticle is molted and exocuticle is dissolved (is this true for all Enoplia and Chromadorea?).

b. Hypodermis/Epidermis

Hypodermis/epidermis is cellular with cell bodies aggregated in lateral field - resulting in thickening or hypodermal chords under lateral field.
Also thickened in ventral region.
If thickened in dorsal region, usually only in anterior portion.
Hypodermis has hypodermal glands and coelomocytes that are ectodermal in origin. Present in all nematodes. It is speculated that coelomocytes may secrete hormones that control molting of the cuticle.
Hypodermal cells become very active during molting of the cuticle - mitochondria, golgi bodies, etc.

d. 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	some predaceous nematodes
Tubular buccal cavity	some bacterivores
Protrusible spears in two orders: Tylenchida and Dorylaimida	Stomatostyle in Tylenchida Odontostyle, odontophore in Dorylaimida (onchiostyle is obsolete terminology).
Tylenchida:	Dorylaimida:
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.	odontostyle 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 esophageal - from the esophastome. odontostyle often distinguished by referring to it as the spear.

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

Basic structure is corpus, usually muscular (anterior), and postcorpus, with glands (posterior).
Corpus may be further differentiated into procorpus and metacorpus; metacorpus is muscular and may have valves.
Isthmus is a narrower region between metacorpus and postcorpus - surrounded by nerve ring with nerve continuity into dorsal and ventral hypodermal chords.
Cardia or Cardiac Valve is a muscular structure at the base of the esophagus at the opening into the intestine.

Some dorylaimid esophago-intestinal cardia configurations

Cardiac Glands are three glandular bodies located at the base of the esophagus in certain taxa.

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

(ii) Mesenteron:

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

(iii) Proctodeum:

Rectum opens to anus in female, cloaca in male.

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e. Reproductive System

One or two testes (monorchic/diorchic), one or two ovaries (monovarial/diovarial).

(i) Male system:

Testis(es), spicules, gubernaculum, caudal alae are all of diagnostic value.

Testes:

Chromadorea usually have a single testis (except in cases of sex reversal).
Enoplea: usually have two testes, except Order Monhystera and Trichodoridae

Spicules - paired, crescent-shaped, cytoplasm core, nerves. Spread vulva to allow entry of sperm. Their size and shape diagnostic. They may be fused at tip.

Gubernaculum - if present, a guiding structure for spicules, grooved.

Supplements - glands of secretion and attachment. Ventromedian supplements have copulatory function.

Rays - genital papillae embedded in caudal alae in some forms (sensory, tactile function?).

Caudal alae (bursa) - cuticular origin.

Sperm - generally non-flagellate, amoeboid.

(ii) Female system:

Vulval position diagnostic.

One or two ovaries (monovarial/ diovarial), outstretched or reflexed.

Two uteri, opposed - didelphic/ amphidelphic.

One uterus directed forward - monodelphic/prodelphic.

One uterus directed backward - monodelphic/opisthodelphic.

Monodelphic reproductive systems may have a post-uterine sac as a relic of the didelphic system.

Ovaries may show various configurations beyond uteri - outstretched, reflexed, etc. All have the germinal zone at the distal end.

There may be a spermatheca for storage of sperm received in copulation. Usually located between the ovary and uterus.

Between the ovary and uterus is the crustaformeria, a specialized region in which the egg shell is deposited.

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f. Sensory/Nervous System

Nerve ring and associated ganglia in isthmus region.
Largest ganglion is retrovesicular ganglion - the nerve ring.
Nerves are located in the in ventral and dorsal hypodermal chords, embedded between cell bodies.
Nerves conduct signals from sensory structures.

Nematodes have a variety of sensilla:

(i) Amphids

open on or below lips (position of opening is diagnostic).
pouch with sensory neuron.
opening is a pore, slit, spiral, etc.
seem to contain mucoid material.
probably function a chemoreceptors.

(ii) Phasmids

posterior location in lateral field - (chemoreceptors).
occur in Secernentea but not Adenophorea.
scutella are enlarged phasmids in some genera of Tylenchida (e.g., Scutellonema).

(iii) Other Sensilla

have a fairly consistent structure; they include:
elongate setae
sensory pegs
shallow pits
deeper pits (e.g., amphids)
cephalic papillae - on lips - (tactile function?)
cephalic setae - more elongate
somatic setae - rare in Secernentea, but occur in Adenophorea
deirids - in lateral field near nerve ring (tactoreceptors or chemoreceptors)

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g. Excretory System

Simple tubular system - in one or both lateral hupodermal chords in Secernentea; embedded between the three cell bodies in hypodermal chord.

Individual excretory cells or tubular system in Adenophorea.

Excretory pore (external opening of tubular excretory systems) usually visible due to cuticular lining - ventral, position is diagnostic.

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