Download MOLLUSCA

MOLLUSCA
• Phylum Mollusca (mollusks)
• clam, snail, octopus, squid
MOLLUSCA
• marine, freshwater, terrestrial
• protostome developmental characters
• classification conflict: Protostomia vs.
Lophotrochozoa
• body plan: foot, visceral mass, mantle
• Fig. 33.15
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
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
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
GASTROPODA
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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
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
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
GASTROPODA
• change in type of pressure or in tradeoffs causes shifts in directionality of
selection
• selection advantage for shells
– protection against predators
– prevents dessication
• cost: consume calcium, secrete CaCO3
• energetic (physiological) demands
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
BIVALVIA
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Class Bivalvia
clams, mussels, oysters
marine, freshwater
flattened two-part shell
Fig. 33.20
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
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
CEPHALOPODA
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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
ARTHROPODA
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Phylum Arthropoda
crustaceans, spiders, insects
marine, freshwater, terrestrial, aerial
protostome developmental characters
classification conflict: Protostomia vs.
Ecdysozoa
• segmentation
• Fig. 33.29
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
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)
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
ARTHROPODA
• critical component of all ecosystem food
webs; pollinators (insects)
• look at some major groups
• Subphylum Chelicerata (chelicerates)
• horseshoe “crab”, spiders, scorpions,
ticks, mites
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
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
CRUSTACEA
• Subphylum Crustacea (crustaceans)
• crayfish, true crabs, lobsters, shrimp
• marine, freshwater; few terrestrial
CRUSTACEA
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cephalothorax, abdomen; Fig. 33.29
2 pairs of antennae
several pairs of mouthparts
many biramous appendages on
cephalothorax and abdomen; twobranched at the distal portion
CRUSTACEA
• specialization: locomotion, feeding,
respiration (gills)
• larval stages diverse
• copepods: zooplankton (small animals)
• feed on diatoms, dinoflagellates
• key link in marine food webs
UNIRAMIA
• Subphylum Uniramia (uniramians)
• centipedes, millipedes, insects
• terrestrial
UNIRAMIA
• uniramous appendages: 1 unbranched
unit; not branched at distal portion; Fig.
33.35
• 1 pair of antennae
• respiratory system: tracheal system
INSECTA
• Class Insecta: insects
• most speciose of all known life;
probably of all life
INSECTA
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everywhere except oceans
coevolution with angiosperms
head, thorax, abdomen
1 pair antennae; 3 pairs of legs; most
with 2 pairs wings
• Fig. 33.35
INSECTA
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digestive system specialized parts
respiratory system: tracheal system
excretory system: Malpighian tubules
Fig. 44.13
INSECTA
• outfoldings of digestive system
• take wastes from hemolymph and
empty into midgut
• rectum reabsorbs water, nutrients
• dry waste exits anus (conserves water)
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
INSECTA
• metamorphosis; larval, pupal, adult
stages
• Fig. 33.36
BOTFLY
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human botfly (Dermatobia hominis)
female botfly captures female mosquito
glues eggs onto mosquito’s 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)