Transcript Arthropods and Echinoderms

Arthropods and Echinoderms
Biology I: Chapter 28
ARTHROPODS
Arthropods
• Phylum Arthropoda
• Insects, crabs,
centipedes, spiders
• Segmented body
• Tough exoskeleton
made of chitin
• Jointed appendages
Evolution of Arthropods
• Fewer body
segments
• Highly specialized
appendages for
feeding, movement
and other functions
Form and Function in Arthropods
• Complex organ systems; some only found only
in this phylum
• Tracheal tubes (respiration)
• Open circulatory system
• Excrete wastes through saclike tubules
Feeding
• Herbivores, carnivores,
omnivores, bloodsuckers, filter
feeders, detritivores, and
parasites
• Mouthparts have evolved to
allow them to eat anything
imaginable
• Pincers or fangs to sickleshaped jaws that can cut
through the tissues of captured
prey
Respiration: Terrestrial Arthropods
• Tracheal tube: one of many branching, airfilled tubes that extend throughout the body
• Spiracle: small opening located along the
side of the body through which air enters
and leaves the body
• Book lung: organ that has layers of
respiratory tissue stacked like the pages of a
book: used to exchange gases
Respiration: Aquatic Arthropods
• Respire through
feather-like gills
(i.e. lobster and
crabs)
• The horseshoe crab
respires through
organs: book gills
Circulation
• Open circulatory system
• Well-developed heart pumps blood through arteries that branch
and enter the tissues
• Blood leaves the blood vessels and moves through sinuses, or
cavities
• The blood recollects in a large sinus surrounding the heart
• It reenters the heart and is again pumped throughout the body
Excretion
Terrestrial Arthropods
• Malpighian tubules: sac-like organ that
extracts wastes from the blood and adds them
to feces that move through the gut
Aquatic Arthropods
• Diffusion moves cellular wastes from the
arthropod’s body into the surrounding water
Response
• Well-developed
nervous system
• Brain
• Sophisticated sense
organs, (i.e. eyes and
taste receptors)
Movement
• Well-developed groups of muscles
that are coordinated and controlled
by the nervous system
• Allows arthropods to beat their
wings against the air to fly, push
their legs against the ground to
walk, or beat their flippers against
the water to swim
Reproduction
Terrestrial Arthropods
• Internal fertilization
• Sperm or sperm packet
Aquatic Arthropods
• Internal or external fertilization
Growth and Development in Arthropods
Molting
• As the time for molting approaches, skin glands
digest the inner part of the exoskeleton and other
glands secrete a new skeleton
• The animal pulls itself out of the remains of the
original skeleton…this can take several hours
• The new exoskeleton is soft and the animal is
vulnerable to predators
Groups of Arthropods
• Classified based on the number and structure of their
body segments and appendages-particularly their
mouthparts
• Crustaceans
• Spiders and their relatives
• Insects and their relatives
Crustaceans
• 2 pairs of branched antennae
• 2-3 body sections
• Mandibles: chewing mouthparts
• Primarily aquatic
• Examples: Crabs, shrimps, lobsters, crayfishes, and barnacles
• Range in size from small terrestrial pill bugs to spider crabs that
have masses around 20 kg
Crustaceans
• Cephalothorax: region of a
crustacean formed by the
fusion of the head with the
thorax
• Thorax: body part of
crustacean that lies just
behind the head and houses
most of the internal organs
• Abdomen: posterior part of
an arthropod’s body
Crustaceans
• Carapace: the part of the
exoskeleton that covers the
cephalothorax
• Mandible: mouthpart adapted for
biting and grinding food
• Cheliped: one of the first pair of
legs of decapods (five pairs of
legs: crayfishes, lobsters and
crabs)
• Swimmerets: flipper-like
appendages used by decapods for
swimming
Spiders and Their Relatives
• Chelicerates
• Mouthparts: chelicerae
• 2 body sections
• 4 pairs of walking legs
• Horseshoe crabs, spiders, ticks,
and scorpions
Horseshoe Crabs
• The oldest living arthropods
• First appeared more than
500 mya and have changed
little since that time
• Not true crabs at all! Anatomy
is closer to that of spiders
• Chelicerae, five pairs of walking legs, a long spikelike tail used for movement
Arachnids: Spiders
• The largest group
of arachnids
• Spin webs of a
strong, flexible
protein called silk
• Do not have jaws
for chewing: must
liquefy food to
swallow it
Arachnids: Spiders
• Chelicerae: pair of mouthparts
in chelicerates that contain
fangs and are used to stab and
paralyze prey
• Pedipalps: pair of mouthparts
in chelicerates that are usually
modified to grab prey
• Spinneret: organ in spiders
that contains silk glands
Arachnids: Mites and Ticks
• Small arachnids that are usually parasitic
• Chelicerae and pedipalps are
specialized for digging into a
host’s tissues and sucking out
blood or plant fluids
• Mouthparts are so strong that if you try to pull off a
tick the cephalothorax may separate from the
abdomen and remain in your skin
Arachnids: Scorpions
• Widespread in warm areas around the world
• Have pedipalps that are
enlarged into claws
• The long, segmented
abdomen of a scorpion
carries a venomous stinger
that can kill or paralyze prey
• Chew their prey using their chelicerae
Insects and Their Relatives
• Uniramians have jaws, one pair of antennae, and
unbranched appendages
• A group that contains more species than any other
group of animals living today
• Wide variety of
forms and lifestyles
– Centipedes
– Millipedes
Insects
• Have a body divided into
three parts:
– Head
– Thorax
– Abdomen
• Three pairs of legs are
attached to the thorax
• Like all arthropods,
insects have a segmented
body, exoskeleton, and
jointed appendages
Responses to Stimuli
• Multiple of sense organs are used to respond to
stimuli
• Compound eyes
• Chemical receptors for
taste and smell on their
mouthparts
• Well-developed ears that hear sounds far above the
human range
Adaptations for Feeding
• Three pairs of appendages that are used as mouthparts,
including a pair of mandibles
• Adaptations for
feeding are not
restricted to their
mouthparts
• Many produce saliva containing digestive enzymes
that help break down food
Movement and Flight
• 3 pairs of legs
• Used for walking, jumping, flying, capturing
and holding prey, etc.
• The evolution of flight has allowed insects to
disperse long distances and to colonize a wide
variety of habitats
Metamorphosis
• Incomplete metamorphosis:
type of insect development
characterized by a similar
appearance throughout all
stages of the life cycle
• Nymph: immature form that
lacks functional sex organs
and other adult structures
Metamorphosis
• Complete metamorphosis: type of insect development
in which the larvae look and act nothing like their
parents and also feed in completely different ways
• Pupa: stage of
metamorphosis in
which an insect
changes from a
larva into an adult
Insects and Humans
• Many insects are known for their negative effects
• Termites destroy wood structures, moths eat their way
through wool clothing, etc.
• Despite their association with destruction and disease,
insects contribute to agriculture by pollinating 1/3 of
the food that you eat
• Produce commercially valuable silk, wax and honey
Insect Communication
• Communicate using sound, visual,
chemical, and other types of
signals
• Much of the communication
involves finding a mate
• Pheromones: specific chemical
messengers that affect the
behavior of development of other
individuals of the same species
Insect Societies
• Ants, bees, termites, and some of their relatives form
complex associations called societies
• Society: a group of closely related animals of the
same species that work together for the benefit of the
whole group
• Caste: group of individual insects specialized to
perform particular tasks, or roles
ECHINODERMS
Echinoderms
• Phylum Echinodermata
• Live only in the sea
• Spiny skin
• Water vascular system
• Tube feet: suction-cuplike
structures
• Endoskeleton: internal
skeleton; hardened plates of
calcium carbonate
• Five-part radial symmetry
Form and Function in Echinoderms
• The water vascular system, which is filled with fluid,
carries out many essential body functions in
echinoderms including respiration, circulation, and
movement
• Madreporite: sieve-like structure
through which the water vascular
system of an echinoderm opens to
the outside
Feeding
• Several methods of feeding
• Sea urchins use five-part
jaw-like structures to scrape
algae from rocks
• Sea lilies use tube feet to
capture floating plankton
• Sea stars feed on mollusks by pushing the stomach
out through the mouth
Respiration and Circulation
• Other than the water vascular system,
echinoderms have few adaptations to carry out
respiration or circulation
• In most species, the
thin-walled tissue of
the tube feet provides
the main surface for
respiration
Excretion
• Solid wastes are released as feces through the
anus
• Nitrogen-containing cellular wastes are
excreted primarily in the form of ammonia
• It is passed through the tube feet and skin gills
Response
• Do not have a highly developed nervous system
• Most have a nerve ring that surrounds the mouth and
radial nerves that connect the ring with the body
sections
• Most have scattered sensory cells that detect light,
gravity, and chemicals released by potential prey
Movement
• Most move by tube
feet and thin layers
of muscle fibers
attached to their
endoskeleton
• Mobility is
determined by the
kind of endoskeleton
Reproduction
• Reproduce by external fertilization
• The sexes are separate in most sea star species
Groups of Echinoderms
• 7000 species
– Sea urchins and sand dollars
– Brittle stars
– Sea cucumbers
– Sea stars
– Sea lilies and feather stars
Ecology of Echinoderms
• Common in a variety of marine habitats
• A rise or fall of echinoderms can cause major changes
to populations of other marine organisms
• Sea urchins control the distribution of algae and other
forms of marine life
• Sea stars are important carnivores that control the
numbers of other organisms such as clams and corals