Arthropods Part 3

Subphylum Myriapoda Class 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

Subphylum Myriapoda Class Diplopoda: Millipedes “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

Millipede

Millipede

Millipede

Giant African Millipede

Subphylum Myriapoda Class 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

Subphylum Myriapoda Class Insecta: Insects 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

Subphylum Myriapoda Class Insecta: Insects 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

Subphylum Myriapoda Class Insecta: Insects 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

Subphylum Myriapoda Class Insecta: Insects 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)

Subphylum Myriapoda Class Insecta: Insects 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

Subphylum Myriapoda Class Insecta: Insects 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

Subphylum Myriapoda Class Insecta: Insects 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

Subphylum Myriapoda Class Insecta: Insects 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

Subphylum Myriapoda Class Insecta: Insects 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