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Mollusca: Symmetry
Bilateral
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Mollusca: # Germ Layers
- 3 (ecto, meso, endoderm)
- protostome
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Mollusca: Metamerism
only in one group
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Mollusca: Coelom
- yes (protostome)
- well developed
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Mollusca: Skeletal System
- none
- hard exoskeleton ( none/reduced in cephalopods)
- CaCO3 shell in most except cephalopods
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Mollusca: Cephalization
- minimal in bivalves
- some in gastropods
- extensive in cephalopods
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Mollusca: Nervous System
- Various, highly developed cephalopods
- limited cephalization (except cephalopods -> highly developed w/ complex sensory system and image forming eyes)
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Mollusca: Digestive System
- complete: specialized for filtering small food particles out of water
- GI tract
- clam: filter-feed with ctenidia, stomach, intestine
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Mollusca: Circulatory System
- hemocyanin dissolved in plasma membrane
- open in bivalves and gastropods
- closes in cephalopods
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Mollusca: Respiratory System
- Ctenidia in most
- sinuses collect hemolymph and transport to ctenidia for gas exchange
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Mollusca: Respiratory Pigment
hemocyanin
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Mollusca: Excretory System
- Nephridia to kidney
- nephrostome (kidney like) -> metanephridia -> metanephridiopore
- nitrogenous wastes excreted into excurrent siphon by pair of kidneys
- some ammonia eliminated by ctendia
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Mollusca: Sexual Cycle
- most dioecious
- pair of gonads empties gametes into excurrent siphon
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Mollusca: Asexual Cycle
none
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Mollusca: Locomotion
- most slow movnig via foot
- Cephalopods fast swimming via jet propulsion
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Mollusca: Classes
- Gastropoda: snail, slug, nudibranch, abalone
- Bivalvia: clams, mussels, scallops
- Cephalopoda: octopi, squid, cuttlefish, nautillus
- Polyplacophora: chitons
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Mollusca: Notes
- heart is located dorsally and is orange
- 100,000 species (2nd largest phylum)
- 540mya
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Shell
- external skeleton
- protects softer parts of animal
- hardened by CaCO3
- internal in cephalopods
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Ctenidia
- lined with cilia
- draws in water into mantle
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Digestive pathway of Bivales
- Water w/ food -> Incurrent siphon -> Mantle cavity -> Ctenidia (lined w/ cilia that beat pulling water in) -> Anus -> excurrent siphon
- stomach , digestive glands, and intestine not visble w/o cutting visceral mass
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Mollusca: Derived features
- mantle
- foot
- radula
- ctenidium
- shell
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Mollusca: Ancestral Features
- protosome development
- bilateral symmetry
- coelomate
- segmentation (some)
- cephalization
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Mantle
- think skin-like structure
- excloses internal organs
- secretes external skeleton (the shell)
- most active secretion at mantle edge -> how shell "grows"
- can repair damaged shell by secreting CaCO3
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Foot
- muscle used for creeping, crawling, grabbing
- modified depending on use
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Radula
- ribbon-like string containing rows of "teeth"
- used for scrapping algae from rocks (limpets)
- tearing into smaller pieces (marine snails)
- harpooning prey (cone snails)
- boring through shells (to eat whats inside)
- new teeth constantly secreted
- Bivalves, some Cephalopods, and snails lack radula
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Ctenidia
- gas exchange and filter feeding (some)
- long feature-like shape with many blood vessels
- filaments extend from central axis to increase SA
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Labial Palps
sorts and transfers food particles into mouth
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