Arthropods and Echinoderms

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Arthropods and Echinoderms

• Biology I Chapter 28

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ARTHROPODS
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Arthropods

• Phylum Arthropoda
• Insects, crabs, centipedes, spiders
• Segmented body
• Tough exoskeleton made of chitin
• Jointed appendages

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Evolution of Arthropods

• Fewer body segments
• Highly specialized appendages for feeding,
  movement and other functions

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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

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Feeding

• Herbivores, carnivores, omnivores, bloodsuckers,
  filter feeders, detritivores, and parasites
• Mouthparts have evolved to allow them to eat
  anything imaginable
• Pincers or fangs to sickle-shaped jaws that can
  cut through the tissues of captured prey

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Respiration Terrestrial Arthropods

• Tracheal tube one of many branching, air-filled
  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

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Respiration Aquatic Arthropods

• Respire through feather-like gills (i.e. lobster
  and crabs)
• The horseshoe crab respires through organs book
  gills

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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

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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
  arthropods body into the surrounding water

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Response

• Well-developed nervous system
• Brain
• Sophisticated sense organs, (i.e. eyes and taste
  receptors)

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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

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Reproduction

• Terrestrial Arthropods
• Internal fertilization
• Sperm or sperm packet
• Aquatic Arthropods
• Internal or external fertilization

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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 skeletonthis can take several hours
• The new exoskeleton is soft and the animal is
  vulnerable to predators

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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

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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

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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 arthropods body

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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

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Spiders and Their Relatives

• Chelicerates
• Mouthparts chelicerae
• 2 body sections
• 4 pairs of walking legs
• Horseshoe crabs, spiders, ticks, and scorpions

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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
  spike-like tail used for movement

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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

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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

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Arachnids Mites and Ticks

• Small arachnids that are usually parasitic
• Chelicerae and pedipalps are
  specialized for digging into a
  hosts 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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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ECHINODERMS
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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

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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

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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

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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

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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

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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

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Movement

• Most move by tube feet and thin layers of muscle
  fibers attached to their endoskeleton
• Mobility is determined by the kind of endoskeleton

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Reproduction

• Reproduce by external fertilization
• The sexes are separate in most sea star species

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Groups of Echinoderms

• 7000 species
• Sea urchins and sand dollars
• Brittle stars
• Sea cucumbers
• Sea stars
• Sea lilies and feather stars

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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