mollusks section 29.1. soft-bodied animals snails, slugs, oysters, clams, scallops, octopuses, squid...
TRANSCRIPT
Soft-bodied Animals
Snails, slugs, oysters, clams, scallops, octopuses, squid
A larval stage called a trochophore Second largest phylum of animals Found in almost all marine, freshwater
and land ecosystems Three major classes: 1. Gastropods2. Bivalves3. Cephalopods
Key Characteristics
1. Body cavity – a true coelom; in most species it is a small area around the heart
2. Symmetry – bilateral3. Three-part body plan – a.) visceral mass: central
section with organs, b.) mantle: heavy outer layer of the body, c.) foot: muscular organ used for movement
4. Organ systems – excretion, circulation, respiration, digestion, reproduction
5. Shell – many have an exoskeleton of 1 or 2 shells made of protein and calcium carbonate
6. Radula – most have a tongue-like organ in the mouth with rows of pointed teeth to scrape food off rocks
Organ Systems
Excretion:
1. Body waste collects in the coelom
2. Cilia moves the fluid into nephridia
3. Fluid is filtered – useful molecules returned to body & fluid wastes leave
Organ Systems, continued…
Circulation: Most have a three-chambered heart
and an open circulatory system Octopuses and squid have a closed
circulatory system
Organ Systems, continued…
Respiration: Most have gills located in the mantle
cavity Land snails have no gills – but the
mantle cavity acts as a primitive lung
Organ Systems, continued…
Reproduction Most have males and females – some
snails and slugs are hermaphrodites Some species can change back and
forth between sexes
Gastropods
“Stomach-foot” Snails and slugs Mainly marine, some in freshwater or
on land Most are herbivores
Bivalves
“Two shells” Clams, oysters, mussels, scallops Two shells are connected to adductor
muscle which can close shell and may also help in swimming
Most are filter feeders which use tubes called siphons to remove food from water
Many of these are important food sources for people
Cephalopods
“Head-foot” Squids, octopuses, cuttlefish, nautiluses Large head attached to tentacles Tentacles have suction cups or hooks The most intelligent of all invertebrates Well-developed eyes similar to
vertebrates