Phylum Arthropoda

• “arthro” = jointed “pod” = foot, appendage• largest phylum of animals on Earth; 3 of 4 animals are

some kind of arthropod• chitinous exoskelton• grow by molting exoskelton• Most are small because shell limits size• Somites fused or combined into functional groups or

tagmata• Most common arthropods are insects (on land) and

crustaceans (in the ocean)

Why have arthropods achieved such great diversity and abundance?

• Versatile exoskeleton• Segmentation and efficient locomotory

appendages• Efficient tracheal respiratory system• Highly developed sensory organs• Complex behavior patterns• Reduced competition through

metamorphosis

Figure 13_02

Ecdysis – process of an arthropod shedding its exoskeleton for reasons of growth and repair of injuries

“soft-shelled crab”

Figure 13_03

Figure 13_04

Subphylum Crustacea

• Great variety of forms; most familiar are shrimp, crabs, lobster

• 2 pair of antennae, calcified exoskeleton, gills

• Some freshwater, but most are marine

                                                         

Less familiar groups of crustaceans

• Copepods – abundant as zooplankton; use enlarged antennae for limited movement

Figure 7.28

Less familiar groups of crustaceans

• Barnacles – sessile filter feeders

• attach to any number of hard surfaces

• filter using feathery cirri• Surrounded by plates

forming a shell

Figure 7.29a

Less familiar groups of crustaceans

• Amphipods – laterally compressed body

• Small; slightly larger than rice grain

• Many found on beaches in seaweed

Figure 7.30

Less familiar groups of crustaceans

• Isopods – dorsoventrally flattened

• Variable in size from rice to shoebox

• One kind eats wood (gribble), another is parasitic (fish lice)

Figure 7.31

                                                                  

Deep sea isopod – “big”

http://photos1.blogger.com/img/265/947/1024/tongue_biter03.jpg

Less familiar groups of crustaceans

• Krill – planktonic and shrimp-like

• up to about 2 inches long• primarily in polar waters• important food source for

many whales, penguins, and fish

Decapods – “10 legs”

• shrimps, lobsters, crabs; largest group of crustaceans in numbers and physical size

• first pairs of legs usually claws• shrimps typically scavengers; many are symbionts as

cleaners with fish and anemones• lobsters are mainly nocturnal and are either

scavengers or predators of molluscs• hermit crabs use snail shells to protect soft abdomen• True crabs with abdomen tucked under shell;

scavengers or predators; swimming crabs vs. walking crabs

Figure 7.32

Red-banded coral shrimp

Penaeid shrimp – “eatin’ shrimp”

Figure 7.36

female

male

Giant hermit crab

Figure 7.37 top

Figure 7.37 bottom

Subphylum Trilobita

• Extinct for about 200 million years• Larval horseshoe crabs closely

resemble trilobites

Subphylum Chelicerata

• Ancient group; horseshoe crabs, sea spiders, spiders, ticks, scorpions

• Two tagmata (carapace and abdomen)• Six pairs of appendages; 1 pair chelicerae,

1 pair pedipalps, 4 pairs of walking legs• No mandibles or antennae• Most suck liquified contents of prey

Class Merostomata

• horseshoe crabs only extant members of this group

• widespread; mainly found in shallow waters with soft bottoms

• forage in mud for worms or scavenge

• Possess a protective carapace and long spinelike telson

• Abdomen possesses layered book gills

Class Arachnida

• Possess six pairs of appendages, the most anterior of which are the chelicerae (fangs in spiders)

• Spiders with cephalothorax and abdomen unsegmented and connected by slender pedicel; possess poison and spin silk; have book lungs

• Scorpions with short cephalothorax that bears the appendages and a segmented abdomen ending in a stinging apparatus

• Ticks and mites with fused cephalothorax and abdomen; most abundant arachnids; many are disease vectors and plant pests

Fig. 33-31

Scorpion

Dust mite

Web-building spider

50 µm

Fig. 33-32

Intestine

HeartDigestivegland

Ovary

Anus

Spinnerets

Silk gland

Gonopore(exit for eggs) Sperm

receptacle

Book lung

Chelicera Pedipalp

Poisongland

Eyes

Brain

Stomach

Subphyla Myriapoda and Hexapoda (formerly Uniramia)

• The myriapods include centipedes and millipedes

• The hexapods include the insects

Subphylum Myriapoda

• The myriapods pods consist of a head and an elongated, segmented trunk

• Possess many uniramous appendages

• Single pair of antennae, mandibles, and one or two pair of maxillae

• Consists of the Classes Chilopoda (centipedes) and Diplopoda (millipedes)

Class Chilopoda - Centipedes

• Centipedes are active predators with fangs that inject venom

• Possess one pair of appendages per segment• Prefer hiding under logs or rocks in moist

environments

Class Diplopoda - millipedes

• Harmless and herbivorous or detritivorous, prefer same environments as centipedes

• Possess two pair of legs per trunk segment

• For defense may release toxic fumes or taste bad

Insects

• Subphylum Hexapoda, insects and relatives, has more species than all other forms of life combined

• They live in almost every terrestrial habitat and in fresh water

• The internal anatomy of an insect includes several complex organ systems

Fig. 33-35

Abdomen Thorax Head

Compound eye

Antennae

Heart

Dorsalartery Crop

Cerebral ganglion

Mouthparts

Nerve cords

Tracheal tubesOvary

Malpighiantubules

Vagina

Anus

• Insects diversified several times following the evolution of flight, adaptation to feeding on gymnosperms, and the expansion of angiosperms

• Insect and plant diversity declined during the Cretaceous extinction, but have been increasing in the 65 million years since

• Flight is one key to the great success of insects• An animal that can fly can escape predators,

find food, and disperse to new habitats much faster than organisms that can only crawl

• Many insects undergo metamorphosis during their development

• In hemimetabolous (incomplete) metamorphosis, the young, called nymphs, resemble adults but are smaller and go through a series of molts until they reach full size

• Insects with holometabolous (complete) metamorphosis have larval stages known by such names as maggot, grub, or caterpillar

• The larval stage looks entirely different from the adult stage

Fig. 33-36

(a) Larva (caterpillar)(b) Pupa

(c) Later-stage pupa (d) Emerging

adult

(e) Adult

• Most insects have separate males and females and reproduce sexually

• Individuals find and recognize members of their own species by bright colors, sound, or odors

• Some insects are beneficial as pollinators, while others are harmful as carriers of diseases, or pests of crops

• Insects are classified into more than 30 orders

Fig. 33-37a

Fig. 33-37b

Fig. 33-37c

Fig. 33-37d

Fig. 33-37e