Nematodes have a complete digestive system comprised of three main parts - the stomodaeum, intestine, and proctodaeum. The stomodaeum includes structures like the mouth, pharynx, and esophagus. The esophagus pumps food into the simple tubular intestine, where digestion and absorption occurs. Undigested waste is expelled through the proctodaeum and anus. Nematodes have different feeding apparatus depending on their lifestyle, such as styles for piercing plant cells or teeth for cutting animal tissues. Their secretory-excretory systems also vary in structure between free-living and parasitic forms.

1. NUTRITION AND
EXCRETION/SECRETION IN PARASITES
Part 2: Nematodes

2. PART 2: NUTRITION IN NEMATODES
 Nematoda possess a recognizable and complete
alimentary system
 Digestive system of nematodes comprised of 3
components
1) Stomodaeum
2) Intestine
3) Proctodaeum
 In a small number of insect parasitic nematodes, the
alimentary canal can be lost completely, under which
conditions the exposed hypodermis of the cuticle
becomes the site for nutrient acquisition le.g.
Mermis, Bradynema).

3. MORPHOLOGY OF A TYPICAL NEMATODE
MALE AND FEMALE

4. STOMODAEUM
 Comprised of mouth, labium, buccal cavity and pharynx
 The mouth is usually a circular opening surrounded by a
maximum of six lips.
 Few parasitic nematodes possess as many as six lips; in
some nematodes lips fuse in pairs to form three.

5.  In many species lips are absent altogether,
 A buccal cavity lies between the mouth and esophagus of
most nematodes.
 The size and shape of this area vary among species and
are important taxonomic characters.

6.  Food ingested by a nematode moves into a esophagus,
or pharynx.
 This is a pumping organ that sucks food into the
alimentary canal and forces it into the intestine.
 Such an arrangement is necessary because of high
pressure in the surrounding pseudocoel.

7.  The esophagus  a variety of
shapes, depending on the
order and species of
nematode, and for this reason
it is an important taxonomic
character.
 It is highly muscular and
cylindrical and often has one
or more enlargements
(bulbs).
 The lumen of the esophagus
is lined with cuticle,

8. Food particles, small enough to pass
through the buccal cavity, are drawn
into the lumen of the metacorpus by
sudden dilation of the procorpus and
metacorpus (a).
Closure of the lumen of the
esophagus in these regions expels
excess water (b), and the mass of
food particles is passed backward
along the isthmus (b, c).
Food is drawn between the bulb flaps
of the posterior bulb by dilation of the
haustrulum, which inverts the bulb
flaps (a) and is passed to the intestine
by closure of the haustrulum and by
dilation, followed by closure of the
pharyngeal-intestinal valve (b).
Bulb flaps contribute to the closure of
the valve in the posterior bulb and,
when they invert (a), also crush food
particles.

9. VARIATIONS IN ESOPHAGI IN SPECIES OF
ASCARIDOID NEMATODES
Nematodes shown are of genera (a) Crossophorus, (b) Angusticaecum, (c)
Toxocara, (d) Porrocaecum, (e) Paradujardinia, ( f ) Multicaecum,
(g) Anisakis, (h) Raphidascaris, (i) Contracaecum. v, ventriculus.

10. INTESTINE
 The intestine is a simple, tube like structure extending
from esophagus to proctodaeum.
 Constructed of a single layer of intestinal cells.
 In females a short, terminal, cuticle-lined rectum runs
between anus and intestine.
 In males the rectum receives products of the reproductive
system into its terminal portion  cloaca.

11.  The intestine is nonmuscular.
 Its contents are forced posteriorly by action of the
esophagus as it adds more food to the front end of the
system and perhaps by locomotor activity of the worm.
 Internal pressure in the pseudocoel flattens the intestine
when empty.
 Between the dorsal wall of the cloaca and the body wall is
a powerful muscle bundle called depressor ani.

12.  When it contracts, the anus is opened;
 Hydrostatic pressure surrounding the intestine causes
defecation when the anus is opened.
 Hydrostatic pressure expels feces with some force

13.  The wall of the intestine consists of microvilli
 Several digestive enzymes have been identified in
intestinal lumen,
 Intestinal digestion is probably of minor importance in
most forms because of rapid rate of food movement
through the intestine
 The intestine functions by digesting, absorbing water and
nutrients, and eliminating the residues of digestion.

14. Cross section of intestine showing microvilli (M) of dorsal and ventral
sides.
Cellular debris fills the lumen (L)

15. PROCTODAEUM
 Comprised of rectum and anus
 Covered by a layer of cuticle
 The proctodaeum serves as the anus and is where waste is
excreted

16. STRUCTURE AND FUNCTION OF THE FEEDING
APPARATUS
 Feeding apparatus has been a widely used term for the
stoma or mouth in describing nematode feeding
mechanisms
 A feeding apparatus may be classified into four types:
1. Engulfing
2. Piercing
3. Cutting
4. Sucking

17. ENGULFING
 Only mononchid predators possess this type of feeding
apparatus
 Engulf and swallow their prey whole, although they may
also feed by first shredding prey
 The engulfing type consists of two sets of three plates
each located in the buccal cavity

18. A. Feeding apparatus of Anatonchus tridentatus.
B. A. tridentatus engulfing Panagrellus redivivus.
C. Prionchulus punctatus engulfing an entire prey.
D. A. tridentatus ingesting body contents of P. redivivus.

19. PIERCING
 Species with this type of feeding apparatus are known as
stylet-bearing nematodes.
 The main feature of the feeding apparatus is a protrusible
stylet or spear, which is pointed and needle-like with a
narrow lumen connected with the oesophagus.
 Used to pierce plant or fungal cells and suck fluids, but is
also found in some predators, as well as insect and
animal parasites.

20. A. Second-stage juvenile of Heterodera schachtii feeding from the initial
syncytial cell in the root of Brassica napus.
B. Xiphinema diversicaudatum penetrating meristematic cells at
the root tip of Ficus carica seedlings. Arrows show feeding site

21. CUTTING
 This type of feeding apparatus is present in
diplogasterid, actinolaim and enoplid predators and some
animal parasites (e.g. Haemonchus).
 Consists of a buccal cavity armed with a tooth or teeth of
variable sizes located at different positions on the dorsal and
ventral walls.
 Cutting and shredding food into pieces or ripping off tissues
depends upon the size and number of teeth.
 There may be one (e.g. Haemonchus contortus), three (e.g.
Ternidens deminutus) or six teeth (e.g. Streptopharagus
pigmentatus) with sharply pointed (e.g. Triodontophorus) or
rounded tips (e.g. Strongylus vulgaris) or with elaborate ridges
(Strongylus asini).

22. Strongylus vulgaris

23. SUCKING
 The sucking type of feeding is characteristic of bacterial
and carrion feeders.
 Included in this category are
Thelastoma, Mermis, Steinernema and Heterorhabditis
(insect-parasitic nematodes) and Chromodora (marine
nematode).
 The ingestion of nutrients depends upon the
concentration and flow of nutrients, turgor pressure at the
food resource and suction generated by the median
oesophageal bulb.
 E.g Ascaris – suck the contents in the lumen.

24. Ascaris mouth opening
The mouth opening is surrounded by three lips as shown in this
scanning electron micrograph. There is one dorsal lip (A) and two
ventro-lateral lips (B) The yellow arrows point to rows of tiny
denticles on the inner surface of each lip.

25. NEMATODES GROUPS BASED ON FEEDING
 Fungal
 Bacterial
 Predacious
 Unicellular eukaryote
 Insect
 Omnivorous
 Animal
 Plant

26. ANIMALS
 Food of nematodes parasitic in animals includes blood,
tissue cells and fluids, intestinal contents, or some
combination of these.
 Some species parasitic in the intestine feed only on
tissue and not on blood or host ingesta.
 Can be classified into several different groups:
1) Eats up whatever is present in the intestine
2) Eats up liquid tissues/ blood

27. EATS UP WHATEVER IS PRESENT IN THE INTESTINE
 Family Ascarididae
- e.g – Ascaris sp.
- its main food is liquid contents of the intestinal lumen
- e.g Toxocara canis
- Three lips are present

28. SCANNING ELECTRON MICROGRAPH OF TOXOCARA CATI
Note the three lips with sensory papillae
and broad alae at each side.

29. EATS UP LIQUID TISSUES/ BLOOD
 Family Trichuridae
- e.g Trichuris trichiura
- The mouth is a simple opening, lacking lips.
- The buccal cavity is tiny and is provided with a minute
spear.
- The esophagus is very long, occupying about two-
thirds of the body length, and consists of a thin-walled
tube surrounded by large, unicellular glands, or
stichocytes.
- With their anterior ends buried in mucosa, worms feed
on cell contents and blood

30.  Family Capillariidae
- e.g Capillaria hepatica
- parasite of the liver
- causes loss of liver cells
 Family Trichinellidae
- e.g Trichinella sp.
- a short muscular esophagus
- Adults are intramulticellular parasites in intestinal
epithelium
- juveniles reside in nurse cells - juveniles absorb their
nutrients from their enclosing nurse cell

31. SCHEMATIC DRAWING OF AN INTACT NURSE CELL-
PARASITE COMPLEX, SHOWING THE SURROUNDING
CIRCULATORY RETE

32.  Family Ancylostomidae
- Members of this family are commonly known as
hookworms
- They live in their host’s intestine, attaching to the mucosa
and feeding on blood and tissue fluids sucked from it.
- The buccal capsule is large and usually is armed with
cutting plates, teeth, lancets, or a dorsal cone.
- Lips are reduced or absent
- They have a multi-protease cascade to digest host
hemoglobin.
- e.g Ancylostoma caninum, Necator
americanus, Ancylostoma duodenale

33. The mouth of Necator americanus.
Ancylostoma duodenale,
Note the two broad cutting
plates in the ventrolateral
* Patients with heavy infections may lose up to
margins (top).
200 ml of blood per day

34. HOOKWORM ATTACHED TO INTESTINAL MUCOSA.
Notice how the ventral tooth in the depth of the buccal capsule lacerates the
host tissue.

35. Family Trichostrongylidae
- Are small, very slender worms, with a rudimentary buccal
cavity in most cases.
- Lips are reduced or absent, and teeth rarely are present.
- The cuticle of the head may be inflated.
- e.g Haemonchus contortus, Ostertagia spp,
Trichostrongylus spp.

36. Scanning electron micrograph of Ostertagia ostertagia

37.  Family Onchocercidae
- live in tissues of amphibians, reptiles, birds, and
mammals.
- e.g - Wuchereria bancrofti, Brugia malayi, Onchocerca
volvulus, Loa loa, Dirofilaria immitis, Mansonella perstans

38. Wuchereria bancrofti

39. PLANTS
 Nematodes feeding on plants are stylet-bearing, obligate
parasites obtaining nutrients from living cells of
roots, stems or leaves.
 Variations in nematode feeding habits occur for their
adaptive needs.
 Nutrients from living cells and tissues are sucked into the
oesophagus through the stylet lumen
 Some species, stylet is a tooth that lacks a lumen and is
used only to puncture the plant cells

40.  Can be divided into several groups:
1) ectoparasitic
- Ectoparasitic plant feeders obtain nutrition from epidermal
(e.g. Tylenchorhynchus) or endodermal cells (e.g.
Trichodorus, Xiphinema); Psilenchus, Tylenchus and
Atylenchus feed only on root hairs
- Ectoparasites, such as the root lesion nematode
Pratylenchus, feeds on epidermal cells or on root hairs.
ii) migratory ectoparasitic
iii) migratory endoparasitic
- Pratylenchus, Anguina, Radopholus and other migratory
endoparasitic species obtain nutrition from cortical cells
through periodical intercellular migration within the root.

41. iv) sedentary ectoparasitic
- The sedentary ectoparasite Criconemella xenoplax feeds at a
single feeding site on epidermal cells for long durations, causing
little tissue damage, although terminal galls are induced when
feeding occurs at the root tip.
v) sedentary endoparasitic;
- The sedentary endoparasites, such as
Heterodera, Globodera, Meloidogyne or Sphaeronema, establish
complex feeding relationships with their host by modifying host
endodermal cells into specialized feeding structures, such as giant
cells, syncytia or nurse cells.
vi) semi-endoparasitic nematode categories.
- Hoplolaimus and Telotylenchus are semi-endoparasites feeding
internally and externally on plant root tissues.

42. A. Paratrichodorus anemones
feeding on the root hairs of
Nicotiana tabacum.
B. P. anemones feeding on
epidermal cell of N. tabacum.
C. Cross-section of root showing
feeding by Meloidogyne incognita
on a giant cell.
D. Cross-section of tomato root
showing gravid M. incognita
female feeding on a giant cell.
E. Pinewood
nematode, Bursaphelenchus
xylophilus, feeding on fungal
hyphae.
F. Lesion nematode, Pratylenchus
penetrans,
ectoparasitic feeding behaviour
on the root hair of tobacco.
Arrows show site of feeding

43. SECRETORY-EXCRETORY SYSTEM
 So-called excretory systems have been observed in all
nematodes except Trichinellida and Dioctophymatida, but
an excretory function was assigned to the systems in
various nematodes solely on a morphological basis; that
is, the systems simply looked like excretory systems.
 The actual functions of these systems vary according to
the species of nematode and its stage of development

44.  There are no flame cells or nephridia
 The two basic types are glandular and tubular
 The glandular type is typical of free-living groups and may
be involved in secretion of enzymes, proteins, or
mucoproteins.
 Several varieties of tubular excretory systems occur.

45. EXCRETORY SYSTEMS
(a) Single renette in a dorylaimid; (b) two celled renette in Rhabdias spp.; (c)
larval Ancylostoma spp.; (d) rhabditoid type; (e) oxyuroid type; ( f ) Ascaris
spp.; (g) Anisakis spp.; (h) Cephalobus spp.; (i) Tylenchus spp.

46.  Basically, two long canals in the lateral
hypodermis connect to each other by a
transverse canal near the anterior end.
 This transverse canal opens to the exterior by
means of a median ventral duct and pore, the
excretory pore.
 This pore location is fairly constant within a
species and therefore is a useful taxonomic
character.

47.  Ultrastructure of the gland cells clearly suggests secretory
function.
 Enzymes responsible for exsheathment (shedding the old
cuticle at ecdysis) are produced there by various
strongyle juveniles.
 A variety of nematodes excrete substances antigenic for
their hosts through the S-E pores.
 In Nippostrongylus brasiliensis digestive enzymes were
secreted by adult to act in conjunction with the abrading
action of the cuticle.

48.  The major nitrogenous waste product of nematodes is
ammonia
 E.g In normal saline, A. suum excretes 69% of the total
nitrogen excreted as ammonia and 7% as urea.
- Under conditions of osmotic stress, these proportions
can be changed to 27% ammonia and 52% urea.

49.  Amino acids, peptides, and amines may be excreted by
nematodes.
 Other excretory products include carbon dioxide and a
variety of fatty acids.
 The fatty acids are end products of energy metabolism