MOLLUSCA

1
MOLLUSCA

• Phylum Mollusca (mollusks)
• clam, snail, octopus, squid

2
MOLLUSCA

• marine, freshwater, terrestrial
• protostome developmental characters
• classification conflict Protostomia vs.
  Lophotrochozoa
• body plan foot, visceral mass, mantle
• Fig. 33.15

3
MOLLUSCA

• foot muscular, for movement
• visceral mass most of internal organs
• mantle tissue covering visceral mass, secretes a
  shell (calcium carbonate)
• life in a shell
• extension often forms mantle cavity
• mantle cavity gills, anus, excretory pore
• shell for protection minimal muscle attachment
  which limits mobility

4
MOLLUSCA

• radula rasping tongue for scraping
• teeth of chitin point backward on a supporting
  belt
• circulatory system open
• heart directs blood from the gills
• blood sinuses (sinus a hollow) areas where
  blood bathes tissues
• coelom reduced not need hydrostatic skeleton

5
MOLLUSCA

• no segmentation
• dioecious or hermaphroditic
• anterior nerve ring with ganglia (brain) ventral
  paired nerve cords (Fig. 49.2)
• 8 Classes we will examine 3 in lecture

6
GASTROPODA

• Class Gastropoda (snails, slugs)
• most speciose many habitats
• dioecious aquatically
• hermaphroditic terrestrially
• torsion (twist) asymmetrical embryonic
  development
• one side of visceral mass grows faster than
  other Fig. 33.18

7
GASTROPODA

• places visceral mass/shell more centrally over
  body
• two hypotheses regarding selective advantage
• 1) get better head retraction
• 2) get better water flow
• head with eyes at end of tentacles
• terrestrial snails have mantle in mantle cavity
  modified into a lung

8
GASTROPODA

• land slugs reduced or no shell Fig. S7-5
• selection pressures always involve trade-offs
• adaptive structures energetically "expensive" to
  maintain
• why birds on islands become flightless
• why parasites reduce most organ systems

9
GASTROPODA

• change in type of pressure or in trade-offs
  causes shifts in directionality of selection
• selection advantage for shells
• protection against predators
• prevents dessication
• cost consume calcium, secrete CaCO3
• energetic (physiological) demands

10
GASTROPODA

• if moist enviro, dessication pressure reduced
• if low calcium in soil, pressure to conserve for
  other needs
• what about predation pressure which pushes other
  direction?
• shift defense
• already use slime in locomotion, traction
• modified into being distasteful, secrete rapidly,
  when disturbed

11
BIVALVIA

• Class Bivalvia
• clams, mussels, oysters
• marine, freshwater
• flattened two-part shell
• Fig. 33.20

12
BIVALVIA

• 2 valves incurrent, excurrent siphon derived
  from mantle
• powerful adductor muscles
• no distinct head no radula
• adapted for burrowing, filter feeding
• shape of shell, narrow foot allow penetration of
  substrate

13
BIVALVIA

• incurrent siphon brings in water, fine food
  particles
• mucus coating gills traps particles
• cilia transport particles to mouth
• sedimentation (soil erosion) serious threat,
  especially in Illinois
• freshwater mussels
• www.museum.state.il.us/ismdepts/zoology/mussels

14
CEPHALOPODA

• Class Cephalopoda
• squid, octopus marine
• most derived mollusc active carnivores
• only invert. ecological equivalent of fish
• adaptations for greater mobility, hunting prey
• closed circulatory system
• complex nervous system
• largest invert giant squid 40-50 feet long
• homoplasy in eye with vertebratres
• compare Fig. 50.18 with S7-9

15
ARTHROPODA

• Phylum Arthropoda
• crustaceans, spiders, insects
• marine, freshwater, terrestrial, aerial
• protostome developmental characters
• classification conflict Protostomia vs.
  Ecdysozoa
• segmentation
• Fig. 33.29

16
ARTHROPODA

• segments with jointed appendages jointed feet
• segments/appendages show 2 trends
• 1) reduction in number
• 2) increase in specialization (descent with
  modification)
• cuticle exoskeleton of chitin (carbohydrate) and
  protein

17
ARTHROPODA

• segmentation/exoskeleton/specialized jointed
  appendages
• allows rapid, precise movement
• exoskeleton muscle attachment protection from
  predation avoid dessication
• ecdysis shed exoskeleton as grows
• nervous system cephalization
• sense organs
• vision (eyes)
• touch/smell (antennae)

18
ARTHROPODA

• open circ. system heart blood sinuses
  (hemocoel)
• hemolymph bloodlike fluid
• respiratory system gills (aquatic) terrestrial
  book lungs (Fig. 33.32), tracheal system (Fig.
  33.35)
• only dioecious
• most successful metazoan body plan
• based on habitats, species, individuals

19
ARTHROPODA

• critical component of all ecosystem food webs
  pollinators (insects)
• look at some major groups
• Subphylum Chelicerata (chelicerates)
• horseshoe crab, spiders, scorpions, ticks, mites

20
CHELICERATA

• mostly terrestrial few aquatic
• 2 basic body parts cephalothorax (no separate
  head), abdomen
• no appendages on first segment
• 6 pairs of appendages on cephalothorax

21
CHELICERATA

• 1st pair are chelicerae
• chelicerae claw-like appendages near mouth
• functions vary feeding, grasping, fangs, pincers
  
• 2nd pair are pedipalps
• functions vary sensory, feeding, reproduction
• no antennae only simple eyes

22
CRUSTACEA

• Subphylum Crustacea (crustaceans)
• crayfish, true crabs, lobsters, shrimp
• marine, freshwater few terrestrial

23
CRUSTACEA

• cephalothorax, abdomen Fig. 33.29
• 2 pairs of antennae
• several pairs of mouthparts
• many biramous appendages on cephalothorax and
  abdomen two-branched at the distal portion

24
CRUSTACEA

• specialization locomotion, feeding, respiration
  (gills)
• larval stages diverse
• copepods zooplankton (small animals)
• feed on diatoms, dinoflagellates
• key link in marine food webs

25
UNIRAMIA

• Subphylum Uniramia (uniramians)
• centipedes, millipedes, insects
• terrestrial

26
UNIRAMIA

• uniramous appendages 1 unbranched unit not
  branched at distal portion Fig. 33.35
• 1 pair of antennae
• respiratory system tracheal system

27
INSECTA

• Class Insecta insects
• most speciose of all known life probably of all
  life

28
INSECTA

• everywhere except oceans
• coevolution with angiosperms
• head, thorax, abdomen
• 1 pair antennae 3 pairs of legs most with 2
  pairs wings
• Fig. 33.35

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INSECTA

• digestive system specialized parts
• respiratory system tracheal system
• excretory system Malpighian tubules
• Fig. 44.13

30
INSECTA

• outfoldings of digestive system
• take wastes from hemolymph and empty into midgut
• rectum reabsorbs water, nutrients
• dry waste exits anus (conserves water)

31
INSECTA

• nervous system cephalization brain pair of
  ventral nerve cords ganglia
• wings not true appendages extensions of cuticle
• keeps legs free
• many advantages of flight
• dispersal (movement) to new areas
• escape from predators

32
INSECTA

• metamorphosis larval, pupal, adult stages
• Fig. 33.36

33
BOTFLY

• human botfly (Dermatobia hominis)
• female botfly captures female mosquito
• glues eggs onto mosquitos body
• when mosquito begins blood meal, body heat
  triggers hatching of botfly egg
• botfly larva drops onto skin, burrows in
• hooks hold larva in place antibiotic secretion
  prevents bacterial competition
• respiratory spiracle (snorkel)