Nematology 100: LECTURE 2

Rev. 01/01/2020

Anatomy and Morphology

a. Cuticle

• Striations, annulations, punctations.
• Cuticle is proteinaceous with outer lipid layers.
• Lateral field, lines.
• Caudal alae, head ornamentation - probolae.
• There are four molts of the cuticle.
• In Enoplea all layers are molted, in Chromadorea epicuticle is molted and exocuticle is dissolved.

b. Hypodermis (or epidermis)

• Ectoderm in origin.
• Hypodermis/epidermis is cellular with cell bodies aggregated in lateral field - resulting in thickening. Also thickened in ventral region. If thickened in dorsal region, usually in anterior portion.
• Hypodermis has hypodermal glands and coelomocytes that are ectodermal in origin. Present in all nematodes. The glands are speculated to be involved in secreting hormones that control molting.
• Hypodermal cells are very active during molting - mitochondria, golgi bodies, etc.

c. Muscle Layers

• Mesoderm in origin.
• Longitudinal muscles between hypodermal chords.
• Radial muscles in esophagus.
• Valve and sphincter muscles.

d. Digestive System

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

(i) Stomodeum:

    Stoma:

• Lips - hexaradiate - usually six, reduced to 3 in ascarids, 2 in Spirurida. May be extended into probolae and other ornamentation - e.g. Cephaloboidea - Acrobeles.
• Stoma - buccal cavity - movable and immovable armament common in all Nematoda - teeth, etc.
• Globose buccal cavity - some predators.
• Protrusible spears in 3 orders:  Order Rhabditida, Suborder Tylenchina, Dorylaimida, Triplonchida.
• nematodes). Stomatostyle in Order Rhabditida, Suborder Tylenchina; Odontostyle in Dorylaimida, odontophore - located in esophagus but probably originates from a cell that is of stomal origin; Onciostyle consisting of onchium and onchiophore, a grooved to complex tooth in plant-feeding Triplonchida.
• Tylenchina stylet - anterior conical portion with subterminal ventral opening, shaft, knobs.  Cone shed, shaft and knobs resorbed at molt.
• Stomatostyle and odontostyle modified anterior region of esophagus. Terms stomatostyle and odontostyle stem from earlier confusion about origin.
• Tubular stoma in some microbivorous nematodes.

    Esophagus

• 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 narrower region between metacorpus and postcorpus - surrounded by nerve ring with nerve continuity into dorsal and ventral chords.
• Esophagus and glands surrounded by membrane.
• Relationship to intestine (overlap) diagnostic.
• DEGO (dorsal esophageal gland opening) ducted anterior - opens into esophageal lumen or into metacorpus - diagnostic.

(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.

e. Reproductive System

• One or two testes, one or two ovaries - monorchic, diorchic / monovarial, diovarial.
• Male system: testis(es), spicules, gubernaculum, caudal alae all of diagnostic value.
• Chromadorea: usually single testis (except sex reversal).
• Enoplea: usually two testes, except Orders Monhystera and Triplonchida.
• Spicules - paired, crescent-shaped, cytoplasm core, nerves - spread vulva, size, shape diagnostic. - may be fused at tip.
• Gubernaculum - guiding if present, grooved.
• Supplements - glands of secretion and attachment ventromedian - 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
• Female system: vulval position diagnostic; one or two ovaries, outstretched or reflexed - monovarial, diovarial.
• Following terms apply to uteri, not ovaries - often misused: Didelphic - amphidelphic (opposed), prodelphic (directed forward); Monodelphic - prodelphic, opisthodelphic (directed backward)
• Post-uterine sac
• Ovaries, one (monovarial) or two (diovarial), may show various forms and directions beyond uteri - outstretched, reflexed, etc.
• Germinal zone, ovary, spermatheca, crustaformeria, z-organ, uterus.

f. Sensory/nervous System

• Nerve ring and associated ganglia in isthmus region. Largest ganglion is retrovesicular ganglion - the nerve ring.
• Nerves in ventral and dorsal chords, embedded between cell bodies.
• Nerves to sensory structures

Various sensilla:

(i) Amphids -

• open on or below lips;
• opening diagnostic
• pouch with sensory neuron
• Opening pore, slit, spiral, etc.
• Mucoid material absorbs signal?
• Chemoreceptors.

(ii) Phasmids

• in lateral field - (chemoreceptors?) note - scutella
• Secernentea not Adenophorea (does this still apply in Chromadorea vs. Enoplea?)

(iii) Other sensilla

• consistent structure e.g., elongate setae, sensory pegs, shallow pits,deeper pits - Amphids
• Cephalic papillae on head and labial papillae on lips - tactile receptors
• Cephalic setae
• Somatic setae - rare in Secernentea
• Deirids - in lateral field near nerve ring (tactoreceptors or chemoreceptors)

g. Excretory System

• Simple tubular system - in 1 or both lateral chords in Secernentea, embedded between the three cell bodies in hypodermal chord.
• Single cells (hypodermal gland) to tubular in Adenophorea
• Excretory pore usually visible in tubular systems due to cuticular lining - ventral, diagnostic.

Reproductive Strategies

Slides: on nematode anatomy and morphology