Phylum Acanthocephala

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Phylum Acanthocephala
The Spine or Thorny-Headed worms
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Phylogeny
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Acanthocephala

• Characteristics of the Aschelminthes
• Two main groups Molting and non-molting.
• Acanthocephalans and Rotifers are non-molting.
• The molting aschelminthes are related to
  arthropods.
• Pseudocoel formation from persistent blastocoel.
• Does not form by schizocoely or enterocoely (i.e.
  not from true mesoderm).
• Eutely
• Cell division stops at the end of embryonic
  development.
• Growth by increased size, not increased cell
  number.
• Tissues and organs composed of a species
  specific, fixed number of cells.

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Characteristics specific to Acanthocephala

• Spiny or thorny-headed.
• Less than 1,200 species described.
• All are intestinal parasites of vertebrates.
• Common in various fishes (mostly freshwater),
  birds (chickens and turkeys are of economic
  importance), mammals, and a few reptiles and
  amphibians.
• Arthropods sometimes required as intermediate
  hosts.
• Typically cylindrical and small (just a few
  millimeteres up to a few centimeters).
• Constant number of cells, which is species
  specific.
• No specialized respiratory structure.
• Comparatively large pseudocoel.

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The Acanthocephalan Body

• Proboscis.
• Hollow and fluid filled.
• Numerous biochemically hardened hooks or spines.
• Important for species identification.
• Most species have receptacle for retraction.
• Separated from body by septum.
• Brain located at the base of the retractile
  sheath.
• Sensory organs are usually only of a tactile
  nature.
• Not much of a view.

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The Acanthocephalan Body
Close up of the proboscis
Youve got a problem if
How the proboscis attaches to the intestinal wall.
All images from http//www.biosci.ohio-state.edu/
parasite/acanthocephala.html
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The Rest of the Body

• Claim to fame The only protosomes with no
  mouth, anus or gut.
• Food is absorbed from the surrounding intestinal
  juices.
• No circulatory system.
• Excretion system.
• Protonephridia which empty into the bladder.
• Bladder empties into sperm duct in males and into
  the lower part of the uterus in females.
• Skin.
• Covered with muccopolysaccharides and a
  non-cellular cuticle.
• Epidermis has pores that lead to a network of
  channels distributing nutrition.
• Musculature
• Thin outer radial muscles.
• Thicker, inner longitudinal muscles.

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Male Reproductive System

• One ligament sac.
• Two testes located in ligament sac.
• Cement glands.
• Protein that hardens after sperm deposit.
• Penis projects into the bursa.
• Bursa is eversible to grab female.
• Two genital ganglia (nerves) connected by a nerve
  ring.

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Female Reproductive System

• Two ligament sacs, one dorsal and one ventral.
• No defined ovary.
• Fragments called ovarian balls float freely in
  ligament sacs.
• Only mature eggs are able to pass through the
  uterine bell, immature eggs are returned to the
  ligament sac.

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Reproduction The Logistics

• Internal Fertilization.
• The males bursa is wrapped around the females
  posterior end and sperm is deposited.
• Sperm migrates up the vagina to fertilize the
  eggs.
• Proteins from the cement glands harden in the
  vagina, preventing sperm escapees.
• Eggs develop into the acanthor stage, or the
  advanced and differentiated state.
• Ligament sac ruptures and larvae released into
  psuedocoel.
• Larvae passed out through uterine bell
  contractions into the surrounding fluid.
• The hardy larvae can remain viable for several
  months.
• Females can produce more than 1 million eggs in
  her lifetime.

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Development

• Lavae are expelled in the host feces in the
  acanthor stage.
• They have a hard protective shell which provides
  protection and desiccation prevention.
• Most species require development in an
  intermediate host.
• Usually insects for terrestrial life cycles.
• Crustaceans for aquatic.
• When ingested by intermediate, the acanthor
  usually hatches from shell and bores into
  hemocoel (the blood sinus or cavity) for
  development into the cystacanth.
• Adulthood is reached when the intermediate host
  is consumed by the correct vertebrate host thus
  transferring the cystacanth..
• Many species can tolerate ingestion by more than
  one intermediate host.

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Acanthocephalan Classes

• Class Archiacanthocephala.
• Only class with specialized excretory system.
• A cool species Macracanthorhynchus
  hirudinaceus.
• Females can reach up to 70 cm.
• Dont worry, they mainly parasitize swine with
  beetles as intermediate hosts.
• Class Eoacanthocephala
• Mostly parasitize fish with crustaceans as
  intermediates.
• Class Palaeacanthocephala.
• Most specious class.
• Parasitize all vertebrates.
• Alter host behavior???

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Altered Intermediate Host Behavior

• Research has been done on various arthropods
  infected with acanthocephalan parasites.
• Mostly involving cockroaches, crustaceans, fleas
  (amphipods), pillbugs (isopods), and ostracods.
• Behaviors that were significantly changed.
• Amount of activity
• Altered photic response.
• Amount of exposure.
• Substrate color choice.
• Consequences of those behaviors.
• Increased visibility as prey.
• Benefit to parasite.
• Infected arthropods may exhibit atypical
  behaviors in response to parasitic
  (acanthocephalan) infestations, which promote
  predation and the subsequent transfer of the
  parasite to the appropriate, definitive host.