Biology 625
Fall semester lecture note outline

Updated: 24 September 1999

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 #11: Introduction to the Class: Cestoda

  1. Most are parasites of vertebrates (only a couple of genera parasitic in invertebrates)
  2. General morphologic structures
    1. linear series of reproductive structures of both sexes (in most species)
    2. composed of a scolex (head), neck (germinal region), and body (termed a strobila)
    3. most species with (untrue) segments, termed proglottids
      1. craspedote (one proglottid overlaps another)
      2. acraspedote (proglottids do not overlap)
    4. new proglottids added at neck; termed strobilation
    5. as new proglottids form, they move back and gradually mature; copulate with other proglottids (or those of other worms); eggs develop; become gravid and rupture/break off (apolysis)
    6. most monecious
    7. scolex (head)
      1. at anterior end
      2. holdfast organs
        1. suckers
        2. hooks
        3. spines
        4. glands
        5. grooves
      3. sucker-like structures
        1. acetabulum
          1. cup-shaped, muscular
          2. usually 4; sometimes 1 or 2
        2. bothridia
          1. muscular, highly mobile leaf-like structures
          2. usually 4; project from scolex
        3. bothria
          1. shallow pits or grooves
          2. usually 2; up to 6
      4. hooks
        1. keratinized
        2. often in a circle (1-more circles)
        3. often on (often) protrusible, dome-shaped area on scolex termed a rostellum
      5. glands
        1. modified tegumental cells
        2. produce adhesive material
        3. sometimes form discrete apical organ
    8. tegument
      1. absorbs all nutrients since cestodes have no gut
      2. covered by tiny projections to increase surface area (microtriches)
      3. covered by glycocalyx (carbohydrate containing molecules)
        1. enhances host amylase activity
        2. decreases proteolytic activity of host gut proteases
        3. absorbs bile salts, cations
        4. inhibits pancreatic lipase
        5. Overlying syncytium with underlying cytons
      4. both longitudinal and circular muscles; scolex highly muscularized
      5. nerves
        1. unmyelinated
        2. acetylcholinesterase a main neurotransmitter; some 20 different types of neuropeptides also noted
        3. sensory nerves throughout body
        4. ganglia in scolex; highly innervated
        5. longitudinal nerves proceed posteriorly
      6. excretion and osmoregulation
        1. most have 2 pair osmoregulatory canals running posteriorly
        2. dorsal and ventral pairs, unite in scolex
        3. protonephridia embedded throughout each proglottid
      7. basic metabolism
        1. mainly anaerobic
        2. absorbed across tegument
        3. glucose (also galactose) most important; overally, many other not metabolized
        4. amino acids actively transported inside
        5. purines and pyrimidines facilitated diffusion
        6. fatty acids, monoglycerides, and sterols absorbed
      8. Reproductive structures
        1. most monecious with 1 set of male and 1 set of female reproductive structures; few dioecious
        2. few with 1 set of male and 2 sets of female reproductive structures
        3. proglottids gradually mature as the move back
        4. usually male reproductive organs mature first and sperm stored (i.e. after insemination) until ovary matures (protandry or androgyny)
        5. in some, female organs mature first (protogyny or gyandry)
        6. male reproductive structures (testes - vas efferens - vas deferens - internal seminal vesicle - cirrus and cirrus pouch)
        7. female reproductive structures
          1. vitelline follicles with duct (egg shell)
          2. ovary; often a seminal receptacle; uterus
          3. vagina
          4. Mehlis gland and ootype
        8. sperm transfer usually from cirrus to vagina of some segment, or between adjacent strobila. If no vagina, then hypodermic impregnation.

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