crustaceans + mollusks

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phylum of mollusks

MOLLUSCA

classes of mollusks

class bivalvia, class gastropoda, class cephalopoda

characteristics of all mollusks

• soft bodies with an internal or external shell (calcium carbonate)

  • mantle: fleshy material that secretes the shell of the organism

• well defined nervous system + primitive brain

• circulatory system + chambered heart

• digestive system

bivalves traits

• 2 half shells

• large mantle cavity

• large gills — respiration + food

• burrowers

• inhabit mud, silt, sandy bottoms

examples of bivalves

clams, mussels, oysters, scallops

pearl formation in bivalves

• sand or parasite enter the body

• nacre is secreted in layers around the sand/parasite in defense

  • nacre: mother of pearl, what pearls are made of

cephalopod characteristics

• tentacles and arms

• ink sac filled with melanin (defense)

• can use jet propulsion

• large brain w/ developed senses

• sharp beak

• chromatophores (camouflage)

• semi-internal fertilization

cephalopod examples

squid, cuttlefish, octopus, nautilus

what are chromatophores

saccules of pigment surrounded by muscle that contract in order to show as much or as little pigment through the skin as needed

difference between arms and tentacles

arms are short with suckers all throughout, while tentacles are longer with suckers located towards the bottom of the arm

gastropod characteristics

• some have a single shell, some have no shell

• radula (“chainsaw tongue”)

gastropod examples

snails, limpets, slugs, nudibrachs

radula

• tongue-like structure with many tiny teeth

• used to scape algae off rocks and to drill into other shells

gastropod feeding habits

• most are herbivores

• some are predators (oyster drills, whelks)

  • cone snails use a harpoon w/ poison

marine arthropod subphylum

crustaceans

crustacean examples

crab, shrimp, lobsters, crayfish, barnacles

crustacean characteristics

• jointed appendages

• segmented body

• exoskeleton

• open circulatory system

molting

• exoskeletons are hard and stunt growth

• crabs need to shed their exoskeleton when their bodies are too large

• a new skeleton hardens around them over days

• have a 30% increase in body size