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 40. Crustacea

  1. about 30,000 named species, all appear to have been derived from a common ancestor
  2. most aquatic, and development through a naplius larva
  3. 2 pairs of antennae, unlike other arthropods
  4. 1 pair mandibles
  5. 2 pair maxillae
  6. most species with gills
  7. head often indistinct and not separated well from rest of body
  8. all appendages, except sometimes for first set of antennae (antennules) biramous (split into 2 parts)
  9. 2 classes (or superclasses)
    1. Malacostraca (you will not be tested over this taxon)
      1. very few parasitic; most free-living
      2. segmentation distinct
      3. anntenules of some species biramous
      4. 8 somites in thorax
      5. 6 or 7 somites and a telson in abdomin
      6. the first 1-3 thoracic appendages modified into maxillipeds
    2. Maxillopoda
      1. 5 cephalic, 6 thoracic, and 4 abdominal somites plus telson in primitive condition; sometimes segmentation lost secondarily
      2. no appendages normally on abdomin
      3. 5 subclasses and numerous orders
  10. many different taxa that contain parasitic members. However, only a few common representatives will be discussed below

Lernaea cyprinacea (family: Lernaeidae; order: Cyclopoida; subclass: Copepoda)

  1. small family, infecting freshwater fish
  2. many species large
  3. antennae uniramous
  4. mandibles and maxillules biramous
  5. mandibles gnathostomous (short, broad, toothed, and with an open buccal cavity)
  6. life-cycle
    1. males fertilize females
    2. females embed beneath a scale near fin or in mouth. About 1.5 mm long
    3. adults with anterior holdfast organelle comprised of horns derived from cephalothorax/thorax area. These are embedded in dermis of dish (common name = anchor worm)
    4. females gradually grow over 1-2 weeks and can get over 1.5 cm in length. Anchors grow quite large, but legs and mouthparts do not and become dwarfed in size by the growing female; body segmentation becomes indistinct
    5. egg sacs develop at posterior end
    6. nauplii larvae hatch; live off yolk material in their bodies through 3 molts and do not feed
    7. the last nauplii molt results in a copepodid (subadult, similar to adults prior to enlargement); these now seek out a fish, embed, and undergo a series of instars and molts before becoming sexually mature
  7. pathology includes inflammation, ulceration, and sometimes secondary bacterial infections in the skin and underlying muscles; serious threat in fish hatcheries

Ergasilus spp. (family: Ergasilidae; order: Poecilostomatoida; subclass: Copepoda)

  1. ergasilids very common, nearly all parasitic
  2. most common on freshwater fish, although somes species in marine (especially brackish water) fish
  3. antennae of females modified into large, sharp, claw-like structures
  4. females frequently found attached to gills of fish
  5. first pair of legs modified to possess blade-like spines used for rasping off epithelial cells and mucus for consumption
  6. 3 naupliar (free-living) and 5 copepodid (free-living) stages
  7. adult males free-living; female fertilized prior to attaching to fish
  8. may cause severe damage to gill epithelium, loss of respiratory function, and secondary bacterial infections may ensue

Argulus spp. (family: Argulidae; order: Argulidea; subclass: Branchiura)

  1. dorso-ventrally flattened
  2. some over 1 cm in size
  3. many non-host specific
  4. large, prominent sucking discs (2) derived from each of the maxillules
  5. posterior to maxillules are large maxillae apparently used to aid in attachment
  6. piercing stylet, midventral, just posterior to the antennae
  7. females lay eggs on substrate (detach from host to lay eggs)
  8. larvae hatch, first larval stage a juvenile (not nauplius; has been dropped from development)
  9. a morphologically similar taxon (family: Caligidae; order: Siphonostomatoida; subclass: Copepoda) occurs in marine fish. It, too, is dorso-ventrally flattened and can be confused with Argulus spp. However, among other features, sucking discs are absent.

Sacculina spp. (order: Kentrogonida)

  1. parasites of decapods
  2. nauplii larvae are free-living, without a gut, and undergo four molts. Female larval stage then attaches to carapace of decapod, and sheds legs
  3. remaining mass within shell now termed a "kentrogon"
  4. kentrogon internal cell mass then injected into crab hemocoel
  5. cell mass migrates to area dorsal to ventral nerve cord and grows
  6. as it grows it weakens the cuticle, and a gonadal mass of cells protrude through ventral portion of carapace and become external
  7. males attracted and mate with female mass
  8. parasite causes castration and feminization of crab (both male and female crabs affected), and mimics egg mass normally carried ventrally by female crab. Crabs nurture parasite mass as if it were a decapod egg mass. Crab even performs spawning behavior when the time comes for the barnacle larvae to be released

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