Nematology 100: LECTURE 2
Anatomy and Morphology
- Ectoderm in origin.
- Hypodermis/epidermis is cellular with cell bodies aggregated in
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.
- Mesoderm in origin.
- Longitudinal muscles between hypodermal chords.
- Radial muscles in esophagus.
- Valve and sphincter muscles.
- Lips - hexaradiate - usually six, reduced to 3 in ascarids, 2 in Spirurida.
May be extended into
probolae and other ornamentation - e.g. Cephaloboidea -
- 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
- nematodes). Stomatostyle in Order
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
- 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 - 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.
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.
- Simple tubular intestine, surrounded by single layer of endodermal
- Microvilli on inner lining.
- Rectum opens to anus in female,
cloaca in male.
- One or two testes, one or two ovaries - monorchic, diorchic / monovarial,
- Male system: testis(es), spicules,
gubernaculum, caudal alae all of
- 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
- Rays - genital papillae embedded in caudal alae in some forms (sensory,
- 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.
- 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
- open on or below lips;
- opening diagnostic
- pouch with sensory neuron
- Opening pore, slit, spiral, etc.
- Mucoid material absorbs signal?
- in lateral
field - (chemoreceptors?) note - scutella
- Secernentea not Adenophorea (does this still apply in Chromadorea vs.
(iii) Other sensilla
- 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.
Slides: on nematode anatomy and