Chapter 31 Phylum Acanthocephala

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Chapter 31 Phylum Acanthocephala
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• Form and Function
• Throughout their evolution there has been a
  reduction in muscular, nervous, circulatory and
  excretory systems a complete loss of a digestive
  system
• They are pseudocoelomates pseudocoelom is
  essentially filled with reproductive organs

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• General Morphology
• The body consists of an anterior proboscis, a
  neck, and a trunk
• The proboscis is highly variable in shape and is
  covered by numerous sclerotized hooks
• The proboscis is hollow and fluid filled it can
  be everted (extended) or retracted into a
  proboscis receptacle

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• General Morphology cont.
• Lemnisci are paired organs that extend into the
  body cavity from the neck region central canal
  of each lemniscus is continuous with the lacunar
  system
• The lemniscus serves as a fluid reservoir when
  the proboscis is invaginated may also have a
  function in fat metabolism

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• General Morphology cont.
• Located within the receptacle is a nerve
  ganglion that comprises the cerebral ganglion
  (brain)
• The rest of the body, posterior to the neck is
  called the trunk
• Many species have spines embedded in the trunk
  to aid in the attachment to the hosts mucosa of
  the intestine
• The trunk houses the reproductive structures
  also functions in absorbing and distributing
  nutrients

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• Tegument
• The tegument is a syncytium with many functions,
  including protection, inactivation of the hosts
  digestive enzymes by charge effects,
  osmoregulation, concentration of nutrients, ion
  transport, etc
• The outer surface coat is a carbohydrate rich
  glycocalyx
• Closely packed pores at the tegument surface
  lead to pore canals that branch and anastomose

• This fluid filled system of channels is called
  the lacunar system
• Its function is obscure it may be important to
  the body wall musculature or serve as some kind
  of circulatory system

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• Reproductive System
• Male System
• 2 testes, each with vas efferens leading to a
  common vas deferens and/or a small penis
• Males typically have cement glands secrete a
  copulatory cement, allowing the vagina to be
  plugged following sperm transfer
• Males also have a copulatory bursa, a bell
  shaped structure that is typically invaginated
  into the posterior end of the body cavity
• A muscular sac is attached to the bursa and when
  it contracts fluid is forced from the lacuna
  system of the bursa causing it to evert

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• Reproductive System cont.
• Female System
• Ovary is actually fragments of ovarian balls,
  that lie in the ligament sac or pseudocoel
• Posterior end of the ligament sac is attached to
  a muscular uterine bell allows mature eggs to
  pass through into the uterus, vagina, and out the
  genital pore into the feces immature eggs are
  returned to the ligament sac

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• Excretory System
• Protonephidria serve as excretory organs
• Nervous System
• Consists mainly of a ganglion in the proboscis
  sheath and of nerves that connect the ganglion to
  other organs and tissues
• A pair of genital ganglia, with nerves is
  present in the male
• Sense organs are found in the proboscis and in
  the penis and male bursa

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• Early Development
• Fertilized eggs go through early embryological
  development in the ligament sac or pseudocoel
• When eggs emerge from the gonopore they contain
  hooked larvae called the acanthor
• A host must eat the eggs before the embryos can
  hatch
• There is typically one intermediate host no
  free-living stages occur

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• Generalized Life Cycle
• An egg eaten by an arthropod hatches into an
  acanthor, develops into an acathella, becomes a
  juvenile (which may progress to a cystacanth),
  and is eaten by the final, vertebrate host, in
  which it becomes an adult

• Within the invertebrate host, the acanthor is
  liberated from the egg, bores through the gut
  wall, and develops into an acanthella
• The acanthella then becomes a juvenile
• The vertebrate host becomes infected by eating
  the arthropod intermediate host

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• Life Cycle of Moniliformes moniliformes/dubius
• Lives in the small intestine of rats, mice,
  dogs, and cats
• Eggs are eaten by beetles (flour beetles) or
  cockroaches
• Acanthors are deposited in the gut and leave
  with the feces

• If acanthors are ingested by a cockroach, they
  hatche from the shell and penetrate the wall of
  the digestive tract

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• Life Cycle of M. moniliformes/dubius cont.
• They pass through the gut wall, enter the
  homocoel and undergo growth and differentiation
  into an acanthellae
• The acanthellae develop into the infective stage
  - cystacanth

• If a cockroach is eaten by a rodent, it everts
  its proboscis and embeds in the small intestine
• Male and females grow to maturity and copulate
  shelled acanthors then develop in the pseudocoel
  of the female

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• Development in the Cockroach
• The shelled acanthor is stimulated by pH and
  carbon dioxoxide tonicity of the external medium
  to secrete a chitinase which acts upon the chiton
  layer of the shell
• Acanthor then penetrates the gut and goes to the
  hemocoel
• Development in the Rat
• Dormant cystacanth in the cockroach are eaten by
  the rat
• It is then activated by bile salts and
  bicarbonate of the small intestine
• Results in the eversion of the proboscis and its
  attachment to the host mucosa

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• Effects on Behavior
• Cockroaches infected with Moniliformes
  moniliformes move more slowly, travel less and
  spend more time on exposed surfaces
• These behavioral changes apparently increase the
  probability of transmission