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INTRODUCTION Nematodes are a diverse group of worm-like animals. They are found in virtually every environment, both as parasites and as free-living organisms. They are generally minute, but some species can reach several meters in length. Typical nematode structure (courtesy R. Esser).


NEMATODE MORPHOLOGY 1. CUTICLE Striations: transverse incisures allowing flexibility of the cuticle (sometimes called annulations).   Lateral field: lateral lines may run on each  side along the length of the body. The lines are cuticular ridges separated by incisures. Caudal alae : cuticular extensions on either side of, or surrounding, male cloaca. Lateral alae - generally lateral or sub lateral variously along body in both females and males

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Tylenchida with lateral field and longitudinal striae Dorylaimida with longitudinal striae Ascaridida with lateral field extended as longitudinal alae Tylenchida - peloderan (extending to tail tip) Order Tylenchida - leptoderan (anterior to tail tip) Leptoderan caudal alae of Hirschmanniella pomponiensis


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.


CAUDAL GLANDS Caudal Glands are common in adenophorean nematodes.   They secrete adhesive material by which the nematodes can attach to a substrate.   Usually there are three caudal gland cells but the number ranges from two to five.   Caudal gland cells usually share a common orifice, which is closed by a spinneret valve, at the end of the tail. Caudal Glands and Spinneret of Sabateria sp.


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

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(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. 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

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2.Esophagus -Basic structure is corpus, usually muscular (anterior), and post corpus, with glands (posterior ). Corpus may be further differentiated into procorpus and metacorpus. Metacorpus is muscular and may have a valved pump. 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. - 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. P ostcorpus posterior part of the esophagus, consisting of the isthmus and postcorpus bulb.

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(ii) Mesenteron: (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. Simple tubular intestine, surrounded by single layer of endodermal epithelium. Microvilli on inner lining.


NEMATODE TAIL SHAPES Filiform Attenuated with Spinneret Convex- conoid Conoid Conoid, curved Bluntly Conoid Digitate Convex- conoid


Subdigitate Conoid, ventrally arcuate Multidigitate Mucronate Rounded. Cylindroid Cont…


REPRODUCTIVE SYSTEM One or two testes (monorchic/diorchic), one or two ovaries (monovarial/diovarial). ( i) Male system: Single testis (monorchic) or two testes (diorchic),    spicules, gubernaculum, caudal alae are all of diagnostic value. Testes A.  Enoplus sp., Class Enoplea, Subclass Enoplia - paired testes, opposed. B.  Tobrilus sp., Class Enoplea, Subclass Enoplia - paired testes, opposed. C.  Rhabditis sp., Class Chromadorea, Subclass Chromadoria - single testis, reflexed.

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i. Spicules - paired, may be fused at tip. Generally crescent-shaped, with distinct regions, and a  cytoplasm core supplied with nerves.   Their function is to spread vulva to allow entry of sperm.   ii. Gubernaculum If present is a guiding structure for  spicules. Varies in shape. Often grooved. iii. Caudal alae (bursa ) - cuticular in nature Size and shape of spicules varies greatly among taxa. The spicules provide useful diagnostic characters.  The spicules may merely ride against the gubernaculum when extended from the cloaca, or may slide along a track formed by the gubernaculum.

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(ii) Female system: Monovarial system (single ovary) Prodelphic (uterus directed anteriorly) Post-uterine sac present (vestigial posterior uterus, may function as spermatheca) Diovarial system (two ovaries) Amphidelphic (uteri opposed) Ovaries outstretched, not reflexed Two other configurations of the female reproductive system occur: Monovarial , opisthodelphic (uterus directed posteriorly, vulva usually located in anterior region of nematode) Diovarial, prodelphic (vulva usually located at posterior of swollen female) Additionally, ovaries may be variously reflexed and enlarged


SENSORY/NERVOUS SYSTEM Nerve ring and associated ganglia surround esophagus in isthmus region .  Largest ganglion is retro vesicular ganglion - the nerve ring. Ventral and Dorsal Longitudinal Nerves are located in the in ventral and dorsal hypodermal chords, embedded between cell bodies. Nerves conduct signals from sensory structures. i. Amphids: open on or below lips (position of opening is  diagnostic ). pouch with sensory neuron. opening is a pore, slit, spiral, etc. contain mucoid material which is, at least in part, a glycoprotein. The glycoprotein component of the amphid mucus differs among nematode species. function as chemoreceptors. Nematodes have a variety of sensilla: Various shapes of amphid apertures.  More convoluted shapes are thought to enhance sensitivity as chemoreceptors.

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(ii) Phasmids posterior location in lateral field - (chemoreceptors ). scutella are enlarged phasmids in some genera of Tylenchida (e.g., Scutellonema ). pore-like phasmid in lateral field of Rotylenchus robustus (photomicrograph by I.A. Zasada )


EXCRETORY SYSTEM Simple tubular system - in one or both lateral hypodermal ,  embedded between the three cell bodies in hypodermal chord; or an individual cellular system. Excretory canal opens at excretory pore (external opening of tubular excretory systems) is usually visible due to cuticular lining - ventral in mid- to posterior esophageal region; position is diagnostic.   Individual excretory cells systems.


REFERENCES http:// Baldwin, J.G. and H. Hirschmann.  1976.  Comparative fine structure of the stomatal region of males of Meloidogyne incognita and Heterodera glycines .  J. Nematology 8:1-17. Maggenti , A.R. 1981.  General Nematology, Springer Verlag, N.Y. 372p. Premachandran, D., N. Von Mende, R.S. Hussey and M.A. McClure. 1988. A method for staining nematode secretions and structures. Journal of Nematology 20:70-78. Wyss , U. 2002. Feeding behavior of plant-parasitic nematodes. Pp. 233-259. D.L. Lee (ed). The Biology of Nematodes. Taylor and Francis, London. 635p. Zhang, Y.C. and J.G. Baldwin, 2001. Ultrastructure of the postcorpus of the esophagus of Teratocephalus lirellus (Teratocephalida) and its use for interpreting character evolution in Secernentea (Nematoda). Canadian Journal of Zoology 79:16-25.

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