Arthropods Part 3

ARTHROPODS PART 3

Subphylum MyriapodaClass Chilopoda: Centipedes

Active predators Feed mostly on earthworms & insects

Prefer moist places Bodies somewhat flattened

dorsoventrally Contain from a few to 177 segments Each segment bears one pair of

appendages 1st appendages modified to form venom claws

Sexes are separate All are oviparous

Producing eggs that hatch outside the body

“double-footed” Cylindrical bodes contain 25-100

segment Four thoracic segments bear one pair of

legs each Abdominal segments each have two

pairs Herbivores

Decayed plant & animal matter Prefer dark moist places

Subphylum MyriapodaClass Diplopoda: Millipedes

Millipede

Millipede

Millipede

Giant African Millipede

Subphylum MyriapodaClass Insecta: Insects

Most numerous & diverse of all arthropods ~1 million species named

Entomology Study of insects

Differ from other arthropods by: containing 3 pairs of legs 2 pairs of wings

Range from less than 1 mm to 20 cm in length Majority are less than 2.5 cm long

Distribution & Adaptability Live in all habitats that can support life

Only a few are marine Small size & well-protected eggs allow

them to travel great distances by wind, water, & other animals

Cuticular exoskeleton Gives insects much success


External Features Tagmata are head, thorax & abdomen Cuticle composed of 4 plates (sclerites)

Tergum – dorsal notum Ventral sternum Pair of lateral pleura

Legs are often modified for special purposes Terrestrial forms walking legs with terminal pads and

claws as in beetles Can be sticky for walking upside down (house fly) Hind legs adapted for jumping (grasshopper and crickets) First pair of legs modified for burrowing (mole cricket) Paddle-shaped for swimming (water bugs, many beetles) Forelegs modified for grasping pray (praying mantis)


House Fly

Grasshopper

Mole Cricket

Mole Cricket

Praying Mantis eating Grasshopper

Wings & the Flight Mechanism Wings may be:

Thin and membranous (flies) Thick and stiff (beetles) Parchment-like (grasshoppers) Covered with scales (butterflies, moths) With hairs (caddisflies)

Wing movement controlled by thoracic muscles Direct flight muscles

Attached to a part of the wing itself Indirect flight muscles

Not attached tot the wing Cause wing movement by altering the shape of the thorax


Direct Flight Muscles

Indirect Flight Muscles

Wings and Flight Mechanism Flight speeds vary

Fastest flyers usually have narrow, fast-moving wings with a strong tilt

Sphinx moths and horse flies are said to achieve about 48 km/hr (30 miles/hr)

Dragonflies 40 km/hr (25 miles/hr)


Reproduction – Sexes are separate Fertilization is internal They have various means of attracting mates:

Emit a chemical (pheromone) that can be detected for a great distance (moths)

Flashes of lights (fireflies) Sounds and color signals, etc

Sperm are stored in the seminal receptacle of a female numbers sufficient to fertilize more than one batch of

eggs Many insects mate only once during their lifetime


Behavior & Communication Responsive to stimuli are both internal

(physiological) or external (environmental) Much of the behavior is “innate”

entire sequences of actions apparently have been programmed

Insects communicate with other members of their species by chemical, visual, auditory, and tactile signals Chemical signals take the form of “pheromones” Sound production and reception is not present in all

insects Tactile communication includes tapping, stroking,

grasping, and antennae touching


Social Behavior Rank high in the animal kingdom in

the organization of social groups Some groups are temporary and

uncoordinated feeding gatherings of aphids

Some are coordinated for only a brief time

tent caterpillars that join in building a home web and a feeding net

Some have a complex social life honeybees, ants, and termites


Honeybees have one of the most complex social organizations in the insect world Organization continues for a more or less

indefinite period As many as 60,000 to 70,000 may live in a

single hive There are three casts

Queen – a single sexually mature female Drones – a few hundred sexually active males Workers – thousands of sexually inactive

genetic females Take care of young, secrete wax to build the six-sided

cells on the honeycomb, gather nectar from flowers, manufacture honey, collect pollen, and ventilate and guard the hive


Honeybees – Casts are determined partly by fertilization

and partly by what is fed to the larvae Drones develop parthenogenetically from

unfertilized eggs Queens and workers develop from fertilized

eggs “Royal jelly” is fed to larvae that will become queens “Worker jelly” is fed to ordinary larvae

Pheromones from the queen prevent female workers from maturing sexually


Beehive

Queen Bee

Drone Bee

Worker Bee

Worker bee with pollen

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Arthropods Part 3