Transcript Soft-bodied animals that usually have in internal or external shell

Invertebrates
Lesson 9.6
flatworms
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Soft, flattened body, simplest animal to have bilateral symmetry (left and
right sides
Cephalization: most have a head
Materials can diffuse (pass) easily in and out of body
Free-living can be carnivores or scavengers
Parasitic: feed on blood and body fluids or parts of cells in host body.
Free-living worms have eyespots: a group of cells that can detect
differences in light (not a true eye)
Movement: by cilia and muscle cells
Reproduction: most free-living worms are hermaphrodites which have
both male and female reproductive organs
Mollusks
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Soft-bodied animals that usually have in internal or external shell.
Include snails, slugs, clams, squid and octopi
All have a free-swimming larval phase called a trochophore
Common ancestor of mollusks lived more than 550 million years
ago.
• Mollusks have a foot for crawling, burrowing, modified as tentacles
for capturing prey.
• Mantle: thin layer of tissue that covers most of the body.
• Shell: made by glands that secrete calcium carbonate
snail radula
clam siphons
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Radula, a flexible tongue-shaped structure with hundreds of tiny teeth,
used to scrape algae off rocks, drill through shells of other animals, or to
eat prey (squid, octopi)
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Siphon: a tubelike structure through which water enters and leaves the
body to deliver food and for jet propulsion in the squid
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Gills for respiration
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Many mollusks are filter feeders-- can help improve water quality by eating
algae and detritus.
Bivalves
• Two-shelled animals that
include clams, oysters,
mussels and scallops.
• Their shells are held
together by 2 powerful
muscles, the adductor and
abductor.
• Most do not move far;
many burrow into sand and
mud for protection.
• Mussels use byssal
threads to attach to rocks
• SF Bay Area has been
invaded by the zebra
mussel. It can clog water
and sewage pipes.
Gastropods (“gastro” =
stomach)
• Shell-less (nudibranchs)
or single-shelled (snails)
mollusks that move by
using a muscular foot.
• Sea hares protect
themselves by squirting
ink into the water.
• Nudibranchs have
poisons in their skin that
taste bad or make the
predator sick—bright
colors are warnings not to
eat!
Cephalopods:
(“head-foot”)
• The most active mollusks,
including octopi and squid.
• Soft-bodied, with head
attached to a single foot.
This may be separated into
tentacles or arms.
• Most are predators.
• Tentacles have sucking
disks that grab and hold
prey.
• They use fins and siphons
to move swiftly through the
water.
• “Shell” is reduced and
internal
Arthropods
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Most marine arthropods are crustaceans.
These include crabs, shrimp, lobsters, crayfish and barnacles.
Most have 2 pairs of antennae, 2 or 3 body parts and chewing mouthparts
called mandibles
Cephalothorax: head and thorax fused, contains most of internal organs
Abdomen is the posterior (back) part of the body
Mandible: a mouthpart adapted for biting and grinding food
Pincers: large claws modified to catch and cut up food
Swimmerets: appendages used for swimming.
Echinoderms: (clockwise) sea stars, brittle stars, sand
dollars, sea urchins, and sea cucumber (middle)
tube feet
star eating a mussel
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Spiny skin, water vascular system, tube feet, 5-part radial symmetry
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Water vascular system carries out respiration, circulation and movement.
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Madreporite (“mother pore”) is the opening to the outside
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Tube feet act like suction cups to walk and pull open shells of prey
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Sea stars eat by pushing their stomachs out through their mouths,
pouring out digestive enzymes, then digesting the prey in its own shell.
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External fertilization of eggs by sperm in the water
Cnidarians
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The jelly’s larval form is a “polyp,” usually “sessile” (stationary), with its
mouth on top
Adult jelly is a free-swimming bell-shaped “medusa,” with mouth and
tentacles on the bottom.
Sea anemones remain sessile, attached to rocks or sea bottom
All have a primitive nerve net, a gastrovascular cavity for digestion and
stinging cells for catching prey.
Extra slides
Tapeworms
CA DFG
• Long, flat parasitic worms adapted to life in the intestines of the
host. They are surrounded by digested food, so have no digestive
tract, but absorb food directly from the host’s body.
• Body = scolex, a grasping head, and proglottids, or segments.
Tapeworm eggs are released when these segments break off and
burst open.
• Can infest fishes like bass, sharks, rockfish, rays, even whales.
• Tapeworm eggs can be eaten by small crustaceans which are eaten
by fish, and they become infected.
• May become very long: one species in sperm whales can be 50 ft.
long!
Zebra mussel: nationwide infestation
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Small bivalve (0.25-1.5 in) native to Russia– introduced by shipping
Now found across the U.S. in fresh water lakes, streams, reservoirs
Filter out nutrients so native zooplankton and fishes starve
Wastes make water acidic and decrease oxygen– has poisoned
some water birds