Acanthocephalans and Nematomorphids

Question 1

outline the defining features of acanthocephala parasites

Answer 1

thorny headed worms
they posses a retractable proboscis at the anterior end with rows of spines for attaching to the intestinal wall of hosts due to the high turn over of cells and peristalsis movements

= the hook bands and lines can be used to identify the species of acanthocephala

Question 2

outline some characteristics of acanthocephalian parasites

Answer 2

hooks covering the probosic which damage the intestinal lining and cause pathology to host

1100 species described
obligate intestinal parasite of verterbrates (fresh water teleost fish)

intermediate host = arthropods
definitive host= vertebrates

Question 3

why is the distribution of acanthocephala unusual

Answer 3

few individuals will be infected within an area however the individuals which are infected have very large abundances of the parasites within them
= not evenly distributed

Question 4

what is a paratenic host

Answer 4

a host organism which harbours the parasite without allowing it to develop further= used as a transport for the parasite with the hope that it furthers the Lifecyle through trophic relationships ect

Question 5

what species of acanthocephala is most common

Answer 5

Bolbosoma balaenae
krill = intermediate host
definitive host = baleen whale

Question 6

what are the four classes that acanthocephala are divided into

Answer 6

1) ARCHIacanthocephala
2)EOacanthocephala
3) PAELOacanthocephala
4)POLYacanthocephala

= Usually based on taxonomy and morphology of the hook

Question 7

outline the morphology of acanthocephala parasites

Answer 7

= pseudocoelomate animals

= high reproductive capacity (10,000,000 eggs per female)

= size varies from 0.992mm up to 93cm

= dioecious with females being larger than males usually (more room for eggs)

= facultative anaerobes

Question 8

although acanthocephala are closely related to the phyla rotifer why are they different

Answer 8

rotifer are a complex phyla with complex organs and systems

acanthocephalan have shown an evolutionary regression with the digestive tract no longer existing and a reduction in muscular, nervous and circulatory systems
This is because the adults have no use for the complexity= only need to reproduce

Question 9

outline the morphology of the acanthocephala proboscis

Answer 9

everted and inverted which can retract into a sac
= the attachment organ, also used for locomotion
= alternating longitudinal rows of hooks and spines in a specific pattern
= cerebral ganglion in receptacles which control the contraction and retraction of proboscis
= uterine bell which brings eggs into uterus for selective fertilisation

Question 9

outline the characteristics of the species corynosoma cetaceum from the phyla acanthocephala

Answer 9

Definitive host - cetaceans
unlike other species the whole body is covered in spikes/hooks

females are smaller but spikier than males allowing them to be at less risk of being dislodged

indirect data suggests females live longer than the males with sex ratios skewed towards females

Question 9

why are Corynosoma cetaceum
evolved to have their whole body covered in spikes

Answer 9

definitive hosts include dolphins and cetaceans which eat lots of fish at once, this adaptation avoids it from being dislodged in the gut

Question 10

outline the Lifecyle of an acanthocephalan parasite

Answer 10

1) eggs are ingested by the intermediate host (white grubs)

2)the defintive host becomes infected by the ingestion of infected intermediate host, this can also infect humans (usually ones with chaotic lifestyles such as children or mental disorders who eat raw insects)

3) eggs hatch producing larvae and develop into adults which produce eggs shed into the faeces

Question 11

what is an acanthor

Answer 11

contained within the eggs and is a spiny shaped embryo with hooks inside which burrows into the body cavity of the intermediate host

Question 12

how can adult acanthocephala cause trauma to the intestinal mucosa

Answer 12

the proboscis penetrates the intestinal lining with hooks and tends to release and reattach
= complete perforation of the gut can occur which is fatal to mammals
= very painful

can sometimes result in secondary bacterial infections causing haemorrhage or ulcers

Question 13

why are anthelminthics less effective on acanthocephala compared to Platyhelminthes and nematodes

Answer 13

works by paralysing the parasite so it is passed out by natural peristaltic movements
the hooks and spikes allow acanthocephala to remain attached more effectively so less effective

= better to control exposure to definitive host than treat already infected individuals e.g. bio/chemical control to kill of grubs (intermediate host)

Question 14

outline the Lifecyle of the class eoacathnocephala

Answer 14

e.g.Neoechinorhynchus saginatus

• eggs eaten by ostracod crustacean which is the intermediate host
  = eggs hatch within 1 hr and penetrate the gut within 36hrs
• by 16 days the canthella have developed into infective cystacanth
  = these mature in creek chub fish when they ingest crustaceans (definitive host)

Question 15

outline the lifecule of palaeacanthocephala

Answer 15

e.g.Leptorhynchoides thecatus
- eggs are coated in fibres making them sticky becoming entangled in algae
- amphipods ingest eggs with algae where they hatch in the intestine
- amphipods ingested by either definitive or paratenic host where adults attach to gastric cecum

Question 16

outline the Lifecyle of Archiacanthocephala

Answer 16

• eggs eaten by white grubs which are the intermediate host
• hacth in midgut in an hour
• 5-20 days acanthcella is either firee in haemocoel or attached to intestinal lining
• 60-90 days infective cystacanth develop
• pigs (final host) eat grubs r adult metamorphized beetles

Question 17

outline how some acanthocephala can change their host behaviour to increase infection rates

Answer 17

e.g. host amphipods
showed that phototaxic behaviour in amphipods was altered by cystacanths of acanthocephalans polymorphus paradoxus

uninfected= photophobic and moved towards gravity

infected= photoactic and moved away from gravity which increases risk of predation by definitive host

e.g. woodlice
infected= attracted to low relative humidity and open areas with no shelter, spent more time in light

Question 18

why are parasitic infections in humans by acanthocephalans rare

Answer 18

few people eat raw beetles or cockroaches
only 7 species infect humans
= usually associated with times of famine where people eat raw insects

Question 19

outline some characteristics of the phyla nematomorpha

Answer 19

• superficially similar to the morphology of nematodes
  = two orders
  1) nectonematoidea = pelagic in costal marine habitats
  2) gordioidea = freshwater and semiterrestrial
  • 1-3mm in diameter and around 30cm in length
• non-functional digestive tract and appear to lack excretory mechanism= evolutionary regression
• adults are free living
• larvae known to alter host behaviour causing them to jump into water allowing adult to esacpe and reproduce

Question 20

outline the morphology of nectonematoideas

Answer 20

• double row of natatory setae on each side
• dorsal and ventral longitudinal epidermal cords
• fluid filled pseudocoelom
• larvae parasitic to decapod crustaceans

Question 21

what is the sexual dimorphism between male and female nematomorphids

Answer 21

both have a cloacal pore
females have caudal lobes depending on the species

Question 22

outline reproductive methods in nematomorphids

Answer 22

Females remain inactive, males highly motile during breeding period

Male wraps his body around female, deposits a drop of sperm
near the cloacal pore.

Sperm can be stored by the female while the eggs mature, then the
eggs are fertilised internally.

Eggs laid in gelatinous strings

Larvae develop inside the eggs; emerges and actively seeks an
arthropod host

*probably* arthropod attempts to eat the larvae

Some cases of active penetration of host cuticle