Phylum Arthropoda

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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)

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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

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Figure 13_02
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Ecdysis process of an arthropod shedding its
exoskeleton for reasons of growth and repair of
injuries soft-shelled crab
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Figure 13_03
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Figure 13_04
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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

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Less familiar groups of crustaceans

• Copepods abundant as zooplankton use enlarged
  antennae for limited movement

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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

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Less familiar groups of crustaceans

• Amphipods laterally compressed body
• Small slightly larger than rice grain
• Many found on beaches in seaweed

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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)

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Deep sea isopod big
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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

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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

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Red-banded coral shrimp
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Penaeid shrimp eatin shrimp
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male
female
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Giant hermit crab
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Subphylum Trilobita

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

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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

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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

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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

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Fig. 33-31
50 µm
Scorpion
Dust mite
Web-building spider
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Fig. 33-32
Stomach
Intestine
Brain
Heart
Digestive gland
Eyes
Ovary
Poison gland
Book lung
Anus
Gonopore (exit for eggs)
Pedipalp
Chelicera
Spinnerets
Sperm receptacle
Silk gland
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Subphyla Myriapoda and Hexapoda (formerly
Uniramia)

• The myriapods include centipedes and millipedes
• The hexapods include the insects

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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)

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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

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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

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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

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Fig. 33-35
Abdomen
Thorax
Head
Compound eye
Antennae
Heart
Cerebral ganglion
Dorsal artery
Crop
Anus
Vagina
Malpighian tubules
Ovary
Tracheal tubes
Mouthparts
Nerve cords
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• 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

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• 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

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• 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

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• 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

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Fig. 33-36
(a) Larva (caterpillar)
(b) Pupa
(c) Later-stage pupa
(d) Emerging adult
(e) Adult
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• 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

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Fig. 33-37a
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Fig. 33-37b
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Fig. 33-37c
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Fig. 33-37d
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Fig. 33-37e