Phylum Acanthocephala

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Phylum Acanthocephala

• The spiny headed worms
• All acanthocephalans are parasites
• Endoparasites
• Pseudocoelomates
• Do not have a digestive tract
• Anterior end formed into an invaginated proboscis
  armed with many hooks.

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Acanthocephala

• Notes adapted from Zoology on Line
  athttp//www.rtis.com/nat/user/elsberry/taxa/acant
  h.htm

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Acanthocephala

• Body is divided into two major regions
• Pre-soma is composed of the proboscis- a
  retractile organ armed with hooks and spines, and
  the neck- an unarmed region  posterior to the
  proboscis.
• Trunk is the major bulk of the animal, surface
  may be smooth, wrinkled, or irregularly ringed
  some genera arm the trunk with spines.

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• Proboscis serves as an organ of attachment within
  the hosts intestine or for locomotion.
• Contains alternating rows of hooks and spines in
  a definite pattern.
• Hooks are larger structures with roots sunken
  deep in proboscis walls spines are smaller
  structures lacking roots.
• Proboscis is invaginable and can be withdrawn
  into a muscular sac - the proboscis receptacle.

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Acanthocephala

• Proboscis musculature-
• retractors attach to base of proboscis sheath
  and run posteriorly dividing into ventral and
  dorsal retractors function to withdraw proboscis
  into receptacle.
• protractor originate in a circle at the base of
  neck and attach to posterior end of sheath
  function to extend proboscis out of receptacle.

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Acanthocephala

• Syncytial epidermis has relatively few nuclei
  and cells run together.
• Digestive system- mouth, anus, and digestive tube
  are completely lacking, nutrients taken in via
  pores and diffusion
• Circulatory system is absent
• Excretory system consists of a mass of flame bulb
  protonephridia

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Acanthocephala

• Reproductive system is unique in Acanthocephala
  because the organs are suspended within a
  ligament sac
• All are dioecious with females generally longer
  that males

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Acanthocephala

• Male system
• a. Two testes, two sperm ducts that unite in the
  genital sheath to form the vas deferens which
  ends in a muscular cup, the bursa.
• b. Penis projects into the bursa which is
  eversible to grasp female.
• c. Cement glands are present and-drain into the
  sperm duct.
• 4. Female system
• a. Fragmented ovaries are unattached in liagament
  sac forming free floating ovarian balls.
• b. Ligament sac ruptures when ova are ripe
  sending them into the pseudocoel.
• c. Uterine bell uses peristaltic contractions to
  collect developing eggs and pass them to the
  uterus.
• d. Vagina is also present.

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Acanthocephala

• Sexual Reproduction
• 1. Internal fertilization male bursa is wrapped
  around posterior of the females, cirrus is
  introduced into the gonopore, sperm migrate up
  the vagina, uterus, uterine tube. Male cement
  glands secrete a cement plug sealing up the
  gonopore preventing sperm escape.
• 2. Eggs develop in the pseudocoel until a larval
  stage provided with rostellum and hooks is
  reached hard shell forms.
• 3. Uterine bell contractions pass larvae to
  exterior.
• 4. Expelled eggs are highly resisitant and remain
  viable for months.

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Life Cycle

• A. Vertebrate host- eggs containing partially
  developed acanthors are passed out in feces and
  are ingested by intermediate host.
• B. Intermediate host- usually an arthropod
• 1. Acanthor ruptures from egg, penetrates gut
  wall and lodges in the hemocoel.
• 2. Acanthor develops proboscis and loses hooks,
  now called acanthella.
• 3. Once all the features of the adult are
  developed the animal is termed a cystacanth
  gonads are nonfunctional.
• C. Second vertebrate ingests the intermediate
  host, cystacanth develops to sexual maturity in
  the intestine.

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Ecology and Physiology

• Eggs can withstand temp. of -10 to 45 degrees C.
  and are viable up to three years.
• Number of worms per host is large 1000 in a duck
  intestine.
• Reproductive capacity is high, up to 10,000,000
  eggs per female.
• Very injurious to host as proboscis hooks cause
  damage to intestinal tissues.

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