Biology 625
Fall semester lecture note outline

Updated: 14 March 2005

The text below simply represents a crude lecture outline of one of the topics covered in class. It is not meant to substitute for attending lectures or ignoring the textbook. Additional material, including line drawings, kodachromes, and more extensive information on life-cycles and basic biology, will be supplied in the lectures.

TOPIC 48. Phylum: Acanthocephala (thorny-headed worms)

  1. superficially, similar to nematodes. They also have eutely (constant number of cells making up body).
  2. most closely related to the rotifers
  3. 2 portions
    1. proboscis, which possesses numerous hooks. Size, number, arrangement, and shape of these hooks is important taxonomically. Oncotaxy (study of hooks) is an important diagnostic/taxonomic tool in this phylum. Proboscis extruded and inserted into gut wall; when non-retracted, fits into receptacle. Controlled by retractor muscles and hydrostatic pressure
    2. metasoma (trunk or main body of worm)
  4. tegument (living external layer)
    1. external glycocalyx
    2. syncytial, but no cytons
    3. protects worm and also used to absorb nutrients
  5. 2 sac-like structures anteriorly, lemnisci, with ducts that run anteriorly toward proboscis sheath; unknown function but thought to aid in proboscis extrusion
  6. no digestive system
  7. male reproductive system
    1. 2 testes
    2. copulatory bursa , which is internal and funnel-shaped. It can be extruded hydrostatically and is used to clasp the female during copulation
    3. cement gland(s), which produce(s) a substance the plugs the female vagina following sperm transfer. A copulatory cap is produced which lasts about a week and effectively prevents other males from successfully copulating. Males may also cap the genital area of other males, which prevents them from copulating with females.
  8. female reproductive system
    1. floating ovaries (balls) within a ligament sac. Derived from a single ovary early in life
    2. uterine bell, sorts eggs that enter and only allows those that have matured into the correct size and shape to pass on through to the uterus
    3. sperm enters and migrate into ligament sac. Fertilization of oocytes within the sac
  9. typical life-cycle
    1. eggs pass out female and out of host with feces
    2. eggs either free in environment, or for some aquatic species become entangled via egg coat fibers to algae or other structures
    3. embryonation; larva termed an acanthor (6 or 8 hooks or spines)
    4. eaten by arthropod (i.e. crustacean, insect, etc.)
    5. hatches in intestine; penetrate gut
    6. begins to grow and is now termed an acanthella
    7. the acanthella eventually becomes dormant as a juvenile stage termed a cystacanth
    8. some species utilize paratenic hosts where cystacanth crosses gut and becomes dormant in viscera
    9. cystacanth ingested by definitive host
    10. attaches to gut mucosa; matures
    11. often, juveniles mature in an intestinal site different from that eventually colonized when they become adults
  10. multiple studies have shown that some larval acanthocephala may change the behavior of the intermediate host
    1. Plagiorhynchus cylindraceus causes pillbugs (and other isopods) to reside more commonly in exposed areas and become more susceptible to being eaten by starlings (1984, Sci Am 250(5): 108-115).
    2. Polymorphus paradoxus changes the behavior of the amphipod intermediate hosts which become positively phototaxic (rather than negative) so that they spend more time on the surface of the water and can be ingested more easily by ducks and muskrats
  11. the phylum is divided into 4 classes, the arrangement of which is supported both by genetic and morphologic studies
    1. Archiacanthocephala (most basal group of the phylum)
      1. proboscis retractable except in one order, with hooks on proboscis concentrically arranged
      2. proboscis receptacle single or double walled; brain near middle of proboscis
      3. hypodermal nuclei few in number
      4. male cememt glands separate, eight in number, and pyriform
      5. two persistent ligament sacs in females
      6. major longitudinal lacunar canals median, dorsal and ventral, or dorsal only
      7. eggs oval, usually thick shelled
      8. parasites of birds, mammals
      9. known intermediate hosts insects, myriapods
      10. i.e. Macracanthorhynchus hirudinaceus in swine/white scarabaeid grubs
      11. i.e. Moniliformis moniliformis in rats/cockroaches
      12. other: paratenic hosts common in this taxon
    2. Eoacanthocephala
      1. proboscis retractable, usually small, with few hooks that are radially arranged
      2. proboscis receptacle single walled, with brain near middle or anterior end
      3. hypodermal nuclei few in number, but giant and sometimes amoeboid
      4. male cement glands single and syncytial with several nuclei
      5. two persistent ligament sacs in females
      6. major longitudinal lacunar canals dorsal and ventral
      7. eggs have a variety of shapes
      8. parasites mainly of fish, sometimes amphibia, reptiles
      9. known intermediate hosts usually crustacea
      10. i.e. Neoechinorhynchus cylindratus in many fish including bass and eels/ostracods
      11. i.e. Neoechinorhynchus saginatus in suckers and other freshwater fish/ostracods
      12. other: two orders and four families in this class
    3. Polyacanthocephala
      1. proboscis retractable, long and cylindrical or slightly enlarged anteriorly; hooks many and in longitudinal rows
      2. proboscis receptacle single walled, with brain near middle
      3. hypodermal nuclei many and small
      4. male cement glands elongate pyriform to tubular with giant nuclei
      5. dorsal and ventral ligament sacs in female persistent
      6. major longitudinal lacunar canals dorsal and ventral
      7. eggs oval with numerous radial sculpturings
      8. parasites of South American caimans (3 species). Only cysticanths of the 4th species have been found, and they were found in the body cavity of freshwater fish in Kenya
      9. known intermediate hosts fish (known only for P. kenyensis)
      10. little is known about this class, which contains a single genus (Polyacanthocephala) and 4 species
      11. other: taxonomic reference: Amin, 1987, J. Parasitol. 73: 1216-1219.
    4. Palaeacathocephala
      1. proboscis retractable, with hooks on proboscis as alternating radial rows
      2. proboscis receptacle double walled, with brain near middle or posterior end
      3. hypodermal nuclei fragmented, numerous, and sometimes only found in the anterior one-half of the trunk
      4. male cement glands separate, tubular to spheroid, and usually numbering six
      5. single ligament sac in female ruptures (not persistent) upon sexual maturation
      6. major longitudinal lacunar canals lateral
      7. eggs oval to elongate, and some have a polar thickening of the second membrane
      8. parasites of fish, amphibia, reptiles, birds, mammals
      9. known intermediate hosts usually crustacea
      10. i.e. Plagiorhynchus cylindraceus in passeriform birds/isopods
      11. i.e. Polymorphus paradoxus in ducks and muskrats/amphipods
      12. other: very large and diverse group

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