Bodies divided into three segments: Head, thorax, abdomen
One pair of sensory antenna
Movement
Three pairs of jointed legs along the thorax.
Used for movement, but types vary depending on what they are needed for:
Flies have tiny claws and sticky pads (they can climb on smooth surfaces)
Bees have fuzzy legs (used for collecting pollen)
Most have 2 pairs of chitinous wings (although some have 1 pair and a few wingless species exist)
Only invertebrates that can fly
Flying styles and speeds vary
Butterfly flaps wings 5-6 times per second
Bees flaps wings up to 200 times per second
Flies fly about 8km/h and dragonflies 40 km/h
There are four different types of wings that vary based on need and use
Membranous wings: thin, transparent, and crisscrossed with supporting veins. Most have this type
Membranous Wings
Scale-covered wings: the flight wings of butterflies and moths are covered with delicate, beautifully colored scales that rub off easily
Scale-covered wings
Leatherlike wings: grasshopper’s membranous wings covered by a pair of leather like wings
Leather-like wings
Horny wings: the front wings of beetles are thick shields that cover most of the dorsal surface of the insect
Horny wings
Nutrition
Ingestion:
Variety of different types of mouthparts called mandibles
chewing
sponging
siphoning
piercing
Three main parts of digestive system:
Foregut: food enters through the mouth, it is moistened with secretions from the salivary glands, passes through to the gizzard where it is thoroughly ground
Midgut: gizzard opens into the stomach. Digestive juices digest the food.
Major site of digestion and absorption.
Hindgut: solid residue left in the midgut after digestion passes through the hind gut, or intestine, and out through the rectum and anus
Respiration, circulation, and excretion
Respiratory system of insects is an elaborate system of tubules called tracheae that branch throughout the animal.
This system is so complete that oxygen is transported throughout the animal without using the circulatory system.
These tubules open to the outside through a sereis of spiracles, small pores that run along each side of the animal.
The insect “breathes” as abdominal contractions pump air in and out of the tracheae.
The open circulatory system is only involved in the transport of nourishment and collection of waste. No gas exchange.
Cellular waste is extracted by Malpighian tubes and excreted into the intestine for elimination.
Irritability
Anterior “brain” connected to an anterior ganglion and ventral nerve cord.
Receives information from a variety of sources:
Smell from antennae.
Many insects produce chemicals called pheromones to find a mate.
Antennae can sense humidity and flight speed.
Taste receptors on the mouth parts.
Tactile hairs on the antennae, limbs and body
Compound eyes or several simple eyes
Some have organs to hear
Reprodution
Sexes are separate.
Females store sperm in seminal receptacle
As she lays her eggs they are fertilized
Eggs are protected either by where they are laid (deep in tree bark for example) or with protective coverings.
Metamorphosis
Developmental changes in insects is called metamorphosis.
This permits various stages to perform different functions.
Ex. some insects eat only during their immature forms and become adults only to reproduce.
Only a few species of insects do not exhibit metamorphosis.
Incomplete metamorphosis (grasshoppers)
The nymph that hatches looks like a miniature, oddly proportioned adult.
As it grows and molts it becomes more like the adult.
Same diet and habitat for the nymph and adult.
Complete metamorphosis (90% of all insects)
Involves 4 stages: egg, larva, pupa, and adult
Egg hatches into larva (a segmented wormlike stage)
Some common names: maggots, grubs, caterpillars
After period of eating and molting, the larva enters the pupal stage.
The pupa makes a cocoon around itself (woven silk case).
Though it is quiet on the outside, it is a period of significant activity and grown.
During pupal stage, the organs are dismantled and completely reshaped.
Eventually the cocoon opens revealing a fully developed insect.
All have mouthparts called chelicerae (appear as claws or fangs)
Most are completely harmless (some have painful stings, transmit diseases, or can kill you)
Like insects they have small, compact bodies and long, delicate limbs, but they are not insects.
Here are the characteristics that separate them:
4 pairs of walking legs
Bodies divided into two major segments (cephalothorax and abdomen)
No antennae or mandibles
Respiration by book lungs
Usually 4 pairs of simple eyes
Class Arachnida
Characteristics
6 pairs of appendages:
one pair of chelicerae (with poisonous fangs used to paralyze prey)
one pair of pedipalps used for sensory reception and in males to transfer sperm
4 pairs of walking legs
Nutrition:
All spiders spin silk used for containing eggs, restraining prey, or building a web.
Originates as a liquid protein and is released through organs called spinnerets.
Not all spiders catch prey in their webs. Some prowl on the group and ambush their prey.
Once a spider has they prey, they immobilize them with a bite from the chelicerae and inject digestive juices into the victim.
The spider then sucks up the partially digested tissues using its stomach and pharynx.
Respiration:
Only arachnids have and use book lungs for respiration.
Air enters the spider through a slit in the abdomen and flows between folds of the book lungs where gas is exchanged.
Reproduction:
The sexes are separate. Females are often larger.
Male places his sperm in a tiny web sac and stores it in special cavities of his pedipalps. He then transfers it to the female after a courtship offering of food.
In some species, the female will eat the male after mating.
As she lays her eggs, they are fertilized by the stored sperm.
Most crustaceans are free-living and aquatic (although there are some parasites and terrestrial species).
We are going to look at the crayfish as our example of a crustacean.
The Crayfish
Crayfish
Covered with a tough exoskeleton
Divided into three segments: cephalothorax and the abdomen (composed of 6 different segments)
Beneath the abdomen are a number of paired, small, flipper like appendages called swimmerets (used for swimming and reproduction).
There are four pairs of walking legs and a pair of prominent chelipeds (or pinchers) attached to the cephalothorax.
Life Processes
Movement:
Muscles
Legs
Swimmerets and walking legs
Nutrition:
Scavengers: eating virtually any edible material.
The mouthparts of the crayfish reduce the food to swallowable size.
Then moves to esophagus then to the anterior part of the stomach where it is ground to fine particles by muscular action and chitinous teeth of the gastric mill.
The food is sorted in the posterior part of the stomach.
Food is then moved to the intestines. Undigested food moves through the anus.
Respiration:
The crayfish as two sets of feathery gills found in the two lateral gill chambers along the thorax.
Appendage movement and feathery mouthparts help to keep oxygenated water flowing through the gills.
Blood traveling through the thin-walled gills releases carbon dioxide and absorbs oxygen.
Many can store water in their gill chambers in order to walk on land. The “hold their water” like people “hold their breath.”
Circulation:
Open circulatory system.
Blood collects in the a cavity surrounding the heart.
Blood enters the dorsal heart through tiny openings.
As the heart contracts, valves close to keep the blood from flowing back into the sinus.
The blood then leaves the heart, bathing the organs with oxygenated blood, to then be collected in the sternal sinus.
The blood passes again through the gills and the process starts again.
Excretion:
Excretion is performed by green glands, which are located near the base of the antennas.
The green glands filter out waste.
Fluid wastes are excrete through a pore anterior to the mouth.
Wastes from the intestines are eliminated through the anus.
Response:
Ventral nervous system receives information about the environment from a number of sensory sources.
Compound eyes
Antennae
Antennules, shorter sensory appendages
Tiny bristles for touch on several appendages
Statocyst: the organ of balance found at the base of each anteannule
Reproduction/Regeneration:
Arthropods cannot reproduce asexually, but as a mode of defense, they can loose an appendage and it will grow back.
Crayfish mate in the fall.
The male transfers its sperm to a receptacle in the body of the female using reproductive swimmerets.
The female stores the sperm until she lays her eggs in the spring.
The fertilized eggs are then attached to swimmerets for development. They hatch within 5-6 weeks.
During the first year, crayfish molt seven times. After that, twice a year for 3-8 years until they die.
Phylum Arthropoda includes lobsters, spiders, scorpions, millipedes, and insects. It contains over 1,000,000 species, which is a lot, but scientists believe that only 1/10th of the species have been discovered. It is the most abundant of all the animals.
Why should we study this phylum? They live virtually everywhere and their influence upon man and the environment cannot be ignored. They can destroy crops; produce things like wax, drugs, and silk; help maintain cross fertilization; transmit deadly diseases; and some, like spiders, eat mosquitoes!
Characteristics of phylum arthropoda:
They have an exoskeleton.
Scorpion's Exoskeleton
These are made primarily by chitin, a polysaccharide with strong hydrogen bonds.
Because the exoskeleton is non-living and cannot grow, once the arthropod outgrows their home, they must molt, or shed its covering.
Enzymes are produced to eat away at the inside of the old exoskeleton while a new exoskeleton is produced underneath the old one.
A scorpion molting
They have jointed appendages.
Arthropoda means “joint-footed”
The muscles of the arthropod move the limbs from within its exoskeleton.
Variety or forms and functions:
spider/grasshopper: jumping and locomotion
crabs and lobsters: defense
sensory reception, chewing food, sexual reproduction, etc.
Body segmentation.
Arthropods have three body segments:
Head and thorax (cephalothorax)
Abdomen
Open circulatory system
Dorsal heart
Ventral nervous system
Two ganglia joined into a ventral nerve cord. Protected by not only the exoskeleton, but also the bulk of the animal’s body.
Near the appendages for command and coordination.
Antennae: appendages in the head region that provide taste, smell, and touch.
Sensory bristles
Eyes: compound (thousands of individual lenses) or simple (one lens)
