1. Introduction to Veterinary Helminthology, Platyhelminths, Monogeneans and Trematodes

Platyhelminthes

Nematoda

Acanthocephala

traditional groupings (Phyla) are based on superficial similarities

Phylum Annelida

strictly not regarded as helminths

flatworms

common name of Platyhelminthes

roundworms

common name of Nematoda

thorny-headed worms

common name of Acanthocephala

Class Monogenea

Class Trematoda

Class Cestoda

important groups in Platyhelminthes (3 classes)

Order Ascaridida

Order Oxyurida

Order Rhabditida

Order Enoplida

Order Spirurida

Order Strongylida

important groups in Nematoda (6 orders)

Class Archiacanthocephala

Class Palaeacanthocephala

Class Eoacanthocephala

important groups in Acanthocephala (3 classes)

Subclass Hirudinea

important group in Annelida (1 subclass)

direct and indirect

life cycles of Platyhelminthes and Nematoda

indirect

life cycle of Acanthocephala

direct

life cycle of Annelida

hermaphrodites/monoecious with few exceptions

sexes of Platyhelminthes

separate/dioecious, unisexual

sexes of Nematoda and Acanthocephala

monoecious

sexes of Annelida

dorsoventrally flattened

leaf- or ribbon-like

general body appearance of Platyhelminthes (2)

cylindrical

usually tapering at both ends

general body appearance of Nematoda (2)

cylindrical or flattened

divided into an anterior praesoma and posterior metasome

general body appearance of Acanthocephala (2)

metamerically segmented

dorsoventrally flattened

general body appearance of Annelida

tripoblastic

3 fundamental cell layers (body wall of Platyhelminthes)

tegument

outer layer called a _____ (body wall of Platyhelminthes)

tegument with spines

outer layer in Trematoda (body wall of Platyhelminthes)

tegument with microtriches

outer layer in Cestoda (body wall of Platyhelminthes)

cuticle

hypodermis/epidermis

muscle layer

body wall of Nematoda consists of the: (3)

thick often folded with tegument

body wall of Acanthocephala

cuticle with annulations

body wall of Annelida

present but no posterior opening

digestive tract of trematodes (Platyhelminthes)

absent

digestive tract of cestodes (Platyhelminthes) and Acanthocephala

present

digestive tract of Nematoda and Annelida

Phylum Platyhelminthes

no body cavity

no respiratory and blood-vascular systems

parenchyma

flame cells/solenocytes

not metamerically segmented

Phylum Platyhelminthes

• organs are embedded in a specialized connective tissue known as the _____

• excretory organs - _____

• if segmented → _____

monogeneans/monogenes

Class Monogenea

trematodes/flukes

Class Trematoda

pseudotapeworms

true tapeworms

Class Cestoda (2)

Class Monogenea

mainly occur as ectoparasites of cold-blooded aquatic or amphibious vertebrates and occasionally aquatic invertebrates

direct life cycle

life cycle of Class Monogenea

haptor/opisthaptor

hamuli

uncinuli

morphology

2 cm

Class Monogenea

• adhesive organ - _____

• may bear suckers, anchors (_____), clamps, or hooks/hooklets (_____)

• its _____ is the main basis for identification of monogeneans (monogenes)

• small, rarely longer than _____ long

Polyopisthocotylean monogeneans

Omanicotyle heterospina recovered from the gills of Argyrops spinifer

Family Gyrodactylidae

viviparous monogenean

oviparous

all other monogeneans

serial polyembryony

Russian nesting dolls

larva in uterus of adult may also contain a larva, which in all up to four generations (_____) → _____

operculate

Class Monogenea

• eggs - usually _____, with prolongations or filaments at one or both ends

oncomiridium/onchomiracidium

Class Monogenea

• larva - infective stage

• has cilia and one or more pairs of eyespots

Gyrodactylus

Dactylogyrus

Cichlidogyrus

Diplozoon

Neobenedenia

Benedenia

examples of monogeneans (6)

freshwater

well-developed

pair

16

skin

fin

Gyrodactylus

• in _____ and some marine fish

• haptor - _____; with a _____ of anchors and _____ marginal hooklets

• no eyes

• primarily on _____ and _____

1 pair

14

4

gills

freshwater

Dactylogyrus

• haptor - has _____ of anchors and _____ marginal hooklets

• with _____ eyespots

• mainly in _____ of _____ fishes

gill filaments

cichlids

2 pairs

14

4

posteriorly

Cichlidogyrus

• in _____ of freshwater fish, mainly _____

• _____ of anchors and _____ marginal hooklets

• with _____ eyespots

• ceca join _____

blooding-feeding

gills

cyprinids

adults

Diplozoon

• _____ monogeneans in the _____ of freshwater fish primarily _____

• _____ are permanently fused in pairs

skin

fin

gills

marine

teleosts

elasmobranchs

pair

Neobenedenia and Benedenia

• in _____, _____, and _____ of _____ fish (including _____ or bony fish and _____ or cartilaginous fish)

• with a _____ of anterior adhesive discs

convex

anterior adhesive discs in Neobenedenia

concave

anterior adhesives discs in Benedenia

unsegmented

leaf-like

2

oral sucker

ventral sucker/acetabulum

Class Trematoda

• body - _____ and _____

• organs of attachment - usually _____ suckers (_____ and _____)

mouth

muscular pharynx

2 intestinal ceca

Class Trematoda

• digestive system (3)

2 intestinal ceca

Class Trematoda

• which may or may not have branches

excretory bladder

posterior opening

hermaphrodites

Family Schistosomatidae

Class Trematoda

• flames cells (solenocytes) → _____, which usually have a _____

• _____, except those in the _____

Subclass Asphidogastrea

Subclass Digenea

Subclasses in Class Trematoda (2)

Subclass Asphidogastrea

• parasites of fishes, turtles, mollusks or crustaceans

• mostly direct life cycle

Subclass Digenea

• in terrestrial vertebrates

• indirect life cycle

1 mm

80

large ventral disc

suckerlets

microtubercles

Subclass Asphidogastrea

• _____ to several cm long

• small group with around _____ species

• have a _____ with a large number of small alveoli (_____) or a row of suckers and a tegument with short protrusions, so called _____

molluscs

freshwater bivalves or snails

produce eggs

anterior and posterior sucker

eggs containing larvae

hatched larvae

without

fish

life cycle of Aspidogaster conchicola

• only _____ (_____) are necessary for the completion of the life cycle

• adult worms _____ in which a non-ciliated larva with an _____ develops

• there are conflicting reports on how mollusks become infected: either by _____ or by _____

• the life cycle can be repeated _____ involvement of a vertebrate host, but if a _____ eats an infected molluscs, adults can produce eggs in it

Rugogaster hydrolagi

Subclass Asphidogastrea

• from the rectal glands of the elephant shark or ghost shark Hydrolagus in Tasmania, Australia

• row of transverse grooves (rugae)

Lobatostoma manteri

Subclass Asphidogastrea

• from the intestine of the teleost fish Trachinotus blochi

• anterior head

• adhesive disk consisting of 4 rows of alveoli

0.2 - 130 mm

2

smooth or spiny

metabolically

Subclass Digenea (digeneans/digenes)

• size - _____ long

• usually have _____ suckers (distome, amphistome, monostome)

• tegument - may be _____; _____ active

mouth

pharynx

esophagus

intestinal ceca

anus

Subclass Digenea

• digestive system (5)

few digeneans

have an anus

collecting organ

Subclass Digenea

• excretory system - flame cells; excretory bladder as the _____

circumesophageal ring of fibes

ganglia

forward

backwards

absent

eyespots

tactile function

Subclass Digenea

• nervous system - composed of a _____ and paired _____

• from here, 3 pairs of nerves run _____ and 3 pairs run _____

• sense organs are _____ in the adult

• some larval forms may have _____

• papillae found on the adult tegument may have _____

cirrus

cirrus pouch

prostate glands

seminal vesicle

vas deferens

testes

Subclass Digenea

• male reproductive organs (6)

ovary

receptaculum seminis

Mehlis’ gland

uterus

vitelline glands (vitellaria)

Laure’s canal

ootype

Subclass Digenea

• female reproductive organs (7)

cross-fertilization

self-fertilization

Subclass Digenea

• reproduction - _____ is preferred than _____ when several adult individuals are close together

1 or more

invertebrates

snail

miracidium

sporocyst

redia

cercaria

metacercaria

Subclass Digenea

• life cycle - may have _____ intermediate hosts, usually _____

• the first IH is always a _____

• stages - egg, 1st larva (_____), 2nd larva (_____), 3rd larva (_____), 4th larva (_____), 5th larva (_____), adult

• polyembryony, paedogenesis, parthenogony/parthenogenesis