Download notes

CARTER
Mollusks, Arthropods, and Echinoderms
MOLLUSKS (phylum Mollusca)”soft-bodied”
 Invertebrates with soft, unsegmented bodies, often protected by a hard
outer shell
 thin layer of tissue called a mantle that covers internal organs (mantle
produces shell)
 most move with a muscular structure called a foot (also used for digging or
catching prey); live nearly everywhere; most live in water
 Bilateral symmetry; internal organs; most water-dwelling have gills; many
have an organ call a radula, which is a flexible ribbon of tiny teeth (scientists
use the arrangement of teeth in the radula to help classify mollusks)
 Open circulatory system- blood not always inside vessels; heart pumps
blood into a short vessel that opens into the body spaces containing organs
 Reproduce sexually
 Three major groups: gastropods, bivalves, and cephalopods.
 Gastropods: “stomach foot”; have a single shell (snail) or no shell (slug);
found nearly everywhere; can be herbivores, carnivores, or scavengers
CARTER
 Bivalves: “two-shelled”; do not have radula; are filter feeders (strain their
food from water, like sponges); found in nearly all kinds of watery
environments; oysters, mussels, clams, scallops
CARTER
 Cephalopods: “head-footed”; feet are adapted to form tentacles around the
mouth to capture food; may have an external shell (nautilus), internal shell
(squid), or no shell (octopus); large eyes and excellent vision; most complex
nervous system of any invertebrate (highly intelligent); all live in the ocean
Understanding Check
What organ in a mollusk obtains oxygen from water?
How is the mollusk’s mantle related to its shell?
What are the three groups of mollusks?
CARTER
ARTHROPODS (phylum Arthropoda)-“jointed leg”
 Invertebrates that have an external skeleton (exoskeleton; made of chitin),
segmented bodies, and jointed attachments called appendages (wings,
mouthparts, legs); open circulatory system; most reproduce sexually (male
or female), have internal fertilization (inside the body); shed their
exoskeletons as they grow (molting)
 More species of arthropods than all other animals combined!
 Five classes of arthropods: crustaceans, arachnids, centipedes,
millipedes, and insects.
Crustaceans (Crustacea)
 Two or three body sections; usually has three pairs of appendages for
chewing (mandibles); five or more pairs of legs; two pairs of antennae
 most begin their lives as microscopic, swimming larvae; develop into adults
by metamorphosis ( process in which an animal’s body undergoes
dramatic changes in form during its life cycle)
 found in nearly every kind of watery environment, obtain oxygen through
gills
 many are scavengers, others are predators, some are herbivores
 crabs, barnacles, shrimp
CARTER
Arachnids (Arachnida)
 have two body sections, eight legs, no antennae, breathe with book lungs or
tiny tubes that lead to openings in the exoskeleton; found nearly
everywhere
 spiders, mites, ticks, scorpions
Centipedes (Chilopeda)
 highly segmented body; one pair of legs attached to each segment;
“hundred feet”; predators
CARTER
Millipedes (Diplopeda)
 Highly segmented body; two pairs of legs on each segment; “thousand
feet”; herbivores
------------------------------------------------------------------------------------------------------Understanding Check
Why must arthropods molt?
Insects (Insecta)
 Three body sections (head, thorax, abdomen), six legs, one pair of
antennae, and usually one or two pairs of wings
 Obtain oxygen through a system of tubes (spiracles)
 Begin life as tiny, hard-shelled fertilized eggs, undergo either complete
metamorphosis (four dramatically different stages) or gradual
metamorphosis (no distinctly different larval stage)
CARTER
 Scavengers, herbivores, or carnivores
 Many use camouflage as a defense; vast majority are harmless or beneficial
to humans
 Largest class of animals!
 Flies, ant, mosquito
 Insects serve as decomposers and food
 Insects serve to spread pollen to plants (pollinate); they also spread disease
 Insects can serve as biological controls, controlling pests without using
pesticides (ladybugs controlling aphids)
--------------------------------------------------------------------------------------------------------Understanding Check
What are the three sections of an insect’s body?
How are complete and gradual metamorphosis different?
------------------------------------------------------------------------------------------------------------------------
ECHINODERMS (phylum Echinodermata) “spiny skinned”
 Radial symmetry, parts usually in multiples of five; live on ocean floor
 Most have spiny internal skeleton called endoskeleton
CARTER
 Internal fluid system called a water vascular system; forces water into
structures called tube feet; allow suction cups on the animal to grip rocks
and other structures so that the animal can move
 Do not have a head, are either male or female, and fertilized eggs become
larva which go through metamorphosis
 Some can undergo regeneration of lost body parts
 Sea stars (starfish), sand dollars, sea urchins