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

• 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 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

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• 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• 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

• 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

• 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

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

• 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

• 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• 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)