CHAPTER 34 SECOND PART Flashcards
Phylum Arthropoda
By far the most successful animals
Well over 1,000,000 species (2/3 of all named species)
Arthropods affect all aspects of human life
Divided into four extant classes
Chelicerates, crustaceans, hexapods, and myriapods
Arthropod Morphology
Part of arthropod success explained by Segmentation In some classes specialized into tagmata Head, thorax, abdomen Head and thorax may be fused into cephalothorax or prosoma Exoskeleton Made of chitin and protein Protects against water loss Must undergo ecdysis – molting
Jointed appendages
May be modified into antennae, mouthparts, or wings
Can be extended and retracted
Open circulatory system Nervous system Double chain of segmented ganglia Ventral ganglia control most activities Can eat, move, or copulate with brain removed
Compound eyes are found in many arthropods
Composed of independent visual units called ommatidia
Other arthropods have simple eyes, or ocelli
May be in addition to compound eyes
Have single lenses
Distinguish light from darkness
Respiratory system Many marine arthropods have gills Some tiny arthropods lack any structure for gas exchange Terrestrial arthropods use tracheae Branch into tracheoles in direct contact with cells Connected to the exterior by spiracles Valves control water loss Many spiders use book lungs Leaflike plates
Excretory system
In aquatic arthropods much of the waste diffuses out of gills
Terrestrial insects and some others use Malpighian tubules
Eliminates nitrogenous wastes as concentrated uric acid or guanine
Efficient conservation of water
HEY
Class Chelicerata
Spiders, ticks, mites, scorpions, daddy long-legs, horseshoe crabs, sea spiders
Most anterior appendages called chelicerae
May function as fangs or pincers
Body divided into 2 tagmata
Anterior prosoma bearing all appendages
Pedipalps and 4 pairs of walking legs
Posterior opisthosoma contains reproductive organs
Order Araneae (spiders)
About 35,000 species
Particularly important as predators
Many spiders catch their prey in silk webs
Silk protein forced out of spinnerets found on the posterior of the abdomen
Other spiders actively hunt their prey
All spiders have poison glands with channels through their chelicerae
Order Acari (mites and ticks)
Most diverse of the chelicerates Predators and parasites Most mites are small Cephalothorax and abdomen are fused into an unsegmented ovoid body Ticks are larger Blood-suckers Can carry many diseases Rocky Mountain spotted fever, Lyme disease
Class Crustacea
Largely marine, some freshwater
Crabs, shrimps, lobsters, barnacles, crayfish, copepods, pill bugs, sand fleas
Have three tagmata
Cephalon and thorax fused to form a cephalothorax
2 pairs of antennae, 3 pairs of appendages for chewing, and various pairs of legs
Most appendages are biramous
Gas exchange through gills or across cuticle
All crustaceans but barnacles are gonochoric
Many kinds of copulation
Nauplius stage
Several stages before maturity
Evidence of common ancestor for diverse group
Decapod crustaceans Shrimps, lobsters, crabs, and crayfish Have 10 feet – 5 pairs of thoracic appendages Exoskeleton usually enforced with CaCO3 Cephalothorax covered by carapace Lobsters and crayfish Swimmerets used in reproduction and swimming Uropods paddle on either side of telson Crab has small abdomen held under carapa
Order Cirripedia (Barnacles)
Sessile as adults
Captures food with feathery legs
Hermaphroditic
Longest penis in the animal kingdom relative to size
Class Hexapoda
Insects are by far the largest group of animals
Number of species and number of individuals
More than half of all named animal species
Approximately one billion billion (1018) insects are alive at any one time
External features
Three body regions
Head
Thorax has three segments, each with a pair of legs
May have one or two pairs of wings – outgrowths of body wall
Abdomen
Most insects have compound eyes
Insect mouthparts all have the same basic structure
Modifications reflect feeding habits
Internal organization
The digestive tract is a tube
Digestion takes place in stomach (midgut)
Excretion tales place through Malpighian tubules
Winged insects have dilated tracheae forming air sacs
Form bellows to force air deep into body
Some parasitic or aquatic forms have permanently closed spiracles – use diffusion
Sensory receptors Sensory setae are hairlike structures Detect chemical and mechanical signals Tympanum – a thin membrane associated with tracheal air sacs Detect sound May also use sensory hairs to detect sound Pheromones also used for communication Mating signals, trail markers
Insect life histories Many insects undergo metamorphosis Simple metamorphosis (grasshoppers) Immature stages similar to adults Complete metamorphosis (butterflies) Immature larva are wormlike A resting stage, pupa or chrysalis, precedes the final molt into adult form
JACK
