Download CHAPTER 28 Phylum Arthropoda includes insects, crabs

CHAPTER 28
Phylum Arthropoda includes insects, crabs, centipedes, and spiders. Arthropods have a segmented body, a tough exoskeleton made of
chitin, and jointed appendages, such as legs and antenna. Arthro= jointed pod= foot
Primitive arthropods, like trilobites, had many identical segments, each with a pair of appendages. Evolution favored fewer body
segments and highly specialized appendages for feeding, movement, and other functions.
Feeding: Herbivores, carnivores, omnivores, and parasites.
Circulation: Open circulatory system with well developed heart.
Excretion: Terrestrial (land) arthropods have saclike organs called Malpighian tubules that extract waste from blood, add them to feces
that pass the gut. Aquatic ones just diffuse out of the body.
Respiration: Most terrestrials breathe through branching tracheal tubes that extend through the body. Air enters and leaves the tubes
through small opening along the body called spiracles. Some terrestrials, like spiders, use book lungs- organs that have layers of
stacked respiratory tissue. Aquatics have gills.
Response: All have a brain, most have well developed nervous systems. Many have a compound eye with more than 2000 separate
lenses that detect color and motion very well.
Movement: Well developed muscles at each joint to flex (bend) or extend (straighten) the joint.
Reproduction: Terrestrial have internal fertilization, aquatic have internal or external.
The exoskeleton does not grow with the arthropod. As the arthropod grows, the exoskeleton is molted (shed), and a new, larger one
grows in its place. Skin glands digest the inner part, other glands secrete the new exoskeleton. When the new one is ready, the animal
pulls itself out of the old one. This takes several hours. While the new exoskeleton is still soft, the animal fills with air or fluids to
allow growth before the next molting.
Groups of Arthropods
-Subphylum Crustacea: Crustaceans- crabs, shrimps, lobsters, crayfish, barnacles. Typically have 2 pairs of antennae, two or three
body sections, and chewing mouthparts called mandibles.
Body plan: Two segments- Anterior cephalothorax is a fusion of the head and thorax, which is just behind the head and contains most
internal organs and is covered by the carapace. Posterior segment is the abdomen.
Appendages on cephalothorax: First 2 pair are the antennae. 3rd pair are the mandibles (mouthparts). Crayfish, crabs, and lobsters are
decapods- they have 5 pairs of legs. First pair are the chelipeds, with large claw. Last 4 pair are walking legs.
Appendages on abdomen: Swimmerets used for swimming and fused segments that form paddlelike tail.
-Subphylum Chelicerata:
Class Merostomata: Horseshoe Crabs
Class Arachnida: Spiders, ticks, scorpions Have mouthparts called chelicerae and 2 body sections. Most have 4 pairs of walking legs.
Chelicerates have two pair of mouthpart appendages: Chelicerae- Contain fangs to stab and paralyze prey. Pedipalps- Longer
appendages to grab prey. Respire using book gills (horseshoe crabs) or book lungs (terrestrials).
Horseshoe Crabs: Among oldest living arthropods. Have changed little in 500 million years (called "living fossils"). Look like crabs,
but have all of the appendages of Chelicerates.
Spiders: Largest group of arachnids. No jaws- inject prey with venom from chelicerae to paralyze it, then inject it with digestive
enzymes to break it down. It then "sucks" the tissues out of the prey. All spiders produce silk- uses include webs, cocoons for eggs,
and wrappings for prey. It is stronger than steel!
Mites & Ticks: Parasitic on plants or animals.
Scorpions: Pedipalps are enlarged into claws. Abdomen has a stinger. Can chew their prey with chelicerae.
Subphylum Uniramia: Centipedes, millipedes, and insects. Have jaws, one pair of antennae, and unbranched appendages.
-Class Chilopoda: Centipedes- Many segments, each with one pair of legs.
-Class Diplopoda: Millipedes- Many segments, each with two pairs of legs.
-Class Insecta: Largest number of living species on planet earth!
Insect bodies are divided into 3 segments- head, thorax, and abdomen. Three pair of legs are attached to the thorax. Responses to
stimuli: Insects have many sense organs. Compound eyes detect color and movement extremely well (that's why it's so hard to swat a
fly). They have chemical receptors for smell and taste on their mouthparts, antennae, and legs. They also have ears.
Movement and Flight: The 3 pairs of legs can be adapted for walking, jumping, or capturing and holding prey. Many can fly, usually
with 2 pairs of wings made of chitin.
Metamorphosis: The process of changing shape and form during the growth and development of insects. Two types:
1. Incomplete metamorphosis- Immature form, called nymphs, look much like the adult, but with no sex organs or wings.
2. Complete metamorphosis- Eggs hatch into larvae which look completely different from the adult. Larvae develop into a pupa,
which then develops into an adult.
Insect Communication: Insects use sound, visual, chemical and other signals, primarily to find a mate. Fireflies have a light producing
organ in their abdomen. Crickets chirp by buzzing their wings together. Some insects use chemicals called pheromones to signal
alarms to alert other insects of danger, or to communicate during mating.
Insect Societies: Ants, bees, and termites form complex associations called societies- a group of animals of the same species that work
together for the benefit of the whole group. Each society has a caste system- groups of individuals that are specialized to perform
particular tasks. The basic castes are reproductive females (queen bees that lay all of the eggs), reproductive males (that breed with the
queen), and workers (typically females that do not reproduce).
Communication is important in societies. Social insects use visual, touch, sound, and chemical signals to convey
information. For example, when a worker bee finds a food source, she comes back to the nest, leaving a trail of
pheromones that the rest of the workers can then follow back to the food source. Bees have a "waggle dance", where
they wiggle their abdomen in a particular way to indicate to the other workers the type, quality, direction and distance of a
food source!
Phylum Echinodermata: Sea stars, sea urchins, sand dollars, sea cucumbers. All live in the ocean. Have a spiny skin, internal
skeleton, water vascular system, and tube feet. Radial symmetry as adults, larvae have bilateral symmetry. Movement, respiration, and
circulation are done through the water vascular system. Water enters through the madreporite on the aboral (top) side. Then it moves
into the ring canal, down the radial canal in each arm, into the hundreds of tube feet.
Feeding: Sea stars eat clams and mussels. They use their strong tube feet to pull open the shell. Once open, the star pushes its stomach
out of its mouth and using digestive enzymes digests the mollusk in its shell. It then pulls its stomach back in.
Excretion: Digestive wastes released as feces thru the anus. Nitrogenous waste (urine-like) diffuses through the tube feet and skin
gills.
Response: Do NOT have a highly developed nervous system. Nerve ring surrounds the mouth, with radial nerves down arms. Detect
light, gravity, and chemicals released by prey.
Reproduction: External fertilization.
Groups of Echinoderms:
-Sea Urchins and Sand Dollars- Have large solid plates that surround body. Defense via burrowing ($) or spines (urchin). Grazing
algae eaters.
-Brittle Stars- Filter feeders and detritivores (eating plant/animal decaying remains). Fast moving, can release an arm to distract
predators. Can regenerate limbs.
-Sea Cucumbers: Detritivores and filter feeders. Look like warty, moving pickles!
-Sea Stars: Most are carnivorous. Can regenerate limbs as long as a portion of the central disk remains.
-Sea Lilies & Feather Stars- Filter feeders. Oldest class of echinoderms.