1. Arthropod

2. Phylogeny of Arthropods
Arthropoda
Annelids
(worms)
Onychophorans
(worms w/legs)
Chelicerates
(spiders)
Crustaceans
(lobsters)
Insects
(butterflies)
Trilobites
(extinct)
Worm-like
Ancestor

3. General Characteristics metamerism (segmented body) jointed appendages
bilateral symmetry
secreted exoskeleton
ecdysis (molting)
open circulatory system
ventral nerve cord and brain
                                                         
                                                                                 

4. Subphylum Trilobita (extinct) Subphylum Chelicerata
DIVERSITY
Numbers
about 80% of all animals are arthropods
estimated to be over 30 million arthropods
far more of them than all other metazoan species combined
in virtually every conceivable environment:
marine, terrestrial, freshwater, and aerial habitats.
Phylum Arthropoda
Subphylum Trilobita (extinct)
Subphylum Chelicerata
Subphylum Crustacea
Subphylum Uniramia (insects)

5. Chelicerata
comprises the xiphosurans (horseshoe crabs), arachnids, sea spiders
mostly terrestrial
cephalothorax-abdomen
6 pairs cephalothoracic appendages
chelicerae, pedipalps, 4 pairs legs
no antennae

6. Subphylum Chelicerata
a. Xiphosura (horseshoe crab, Limulus polyphemus)
b. Arachnida
most chelicerates are arachnids
several taxa (orders), many are common and familiar
SCORPIONES (scorpions )
ARANAE (spiders )
OPILIONES (harvestmen, daddy longlegs )
PSEUDOSCORPIONES (pseudoscorpions)
ACARINI (mites and ticks )
c. Pycnogonida (the giant sea spider,
Colossendeis australis)
                                                                

7. Limulus is a benthic scavenger and predator.
Horseshoe Crab
Limulus polyphemus, Carcinoscorpius rotunda, and Tachypleus gigas.
Limulus is a benthic scavenger and predator.
Prey include clams and other invertebrates that it digs for in the sand.
The tail spine is used as a self-righting mechanism if the animal is overturned accidentally. Lives up to 19 years
Reaches sexual maturity at about 9 to 12 years old

8. Horseshoe Crab
Mates during spring and summer full and new moons, onto ocean beaches.
Females lay up to 30 thousand eggs, which males fertilize before burying them in the sand
These eggs provide a major food source for migrating birds along the Atlantic coast. Those that are not eaten hatch during the next high tide, and the tiny larvae are carried away to sea.

9. Subphylum Crustacea a heterogeneous taxon with many subtaxa
two pairs antennae
marine, freshwater, and terrestrial
Primarily aquatic
Free-floating larval stage
26,000+ known species

10. Subphylum Crustacea ANOSTRACA fairy shrimp and brine shrimp PHYLLOPODA
tadpole shrimps, ostracod, water fleas
MALACOSTRACA
the largest, most heterogeneous, and diverse crustacean taxon
shrimps, crabs, lobsters, mantis shrimps, pillbugs, crayfishes
COPEPODA
copepods
enormous ecological importance as planktonic herbivores
CIRRIPEDIA
barnacles

11. Respiration Gills a. General gills are evaginations
typical of aquatic animals
blood is oxygenated by gills
oxygen delivered to tissues by blood
b. Crustacean Gills
crustacean gills are usually associated with appendages
blood circulates through the gill and is oxygenated
c. Book Lungs
present in many arachnid orders
similar to book gills of horseshoe crabs
oxygen transport from the lungs to the tissues is by blood

12. Open Circulatory System
Closed Circulatory System

13. NERVOUS SYSTEM
1. General
nervous system is adapted for the needs of a segmented animal as is that of annelids
annelid and arthropod nervous systems are similar
the similarities may be convergent
2. Arthropod Ground Plan
ladder like nervous system
dorsal brain in the head
a pair of circumenteric connectives that encircle the gut
a paired, ventral, longitudinal nerve cord
paired segmental ganglia
transverse commissures between ganglia
longitudinal connectives
segmental sensory and motor nerves

14. NERVOUS SYSTEM
Side view of body showing relative position of circulatory (yellow), digestive (green), and nervous (blue) systems.

15. SENSE ORGANS
1. General
receptors for light, vibrations, chemicals, equilibrium, gravity
cuticle modified to form a vast array of receptors (sensilla)
2. Sensilla
specialized for various environmental events
consist of:
<>modified cuticle, usually a seta
<> a modified cilium
<> sensory neurons
<> support cells

16. SENSE ORGANS
3. Mechanoreceptors
a. Trichobothria
extremely sensitive mechanoreceptors detect weak, low velocity air currents
a long, slender, solid seta
especially common and important in arachnids
a blinded spider can capture flies using its trichobothria
4. Chemoreceptors
detect chemicals
modified hollow setae with substrate-specific chemosensory neurons
chemoreceptive sensilla resemble mechanoreceptive setae

17. SENSE ORGANS
5. Equilibrium and Gravity
a. Statocysts
several malacostracan crustaceans have statocysts
analogous to the vestibule of the vertebrate inner ear
detects gravitational field and acceleration
6. Tympanal Organs
some arthropods can hear, i.e. detect vibrations in air
tympanal organs are present in several insect groups
cicadas, crickets, grasshoppers, moths
a thin sheet of cuticle (eardrum) over an opening

18. SENSE ORGANS
7. Hygroreceptors
humidity receptors
very important to terrestrial arthropods
8. Photoreceptors
a. General
widespread, often well-developed and sophisticated
two types:
<>"median" pigment-cup ocelli
<>"lateral" compound eyes
<>both often present in the same individual

19. highly variable within the arthropods
SENSE ORGANS
2. Pigment-cup Ocelli
a. General
highly variable within the arthropods
all the receptor units (retina cells) share
a common lens
b. Structure
a cup-shaped layer of pigment-containing cells
encloses a cup-shaped layer of photoreceptor cells known as the retina
concavity of the cup is oriented toward the light source
pigment layer prevents the entry of light from any other direction
a cuticular lens (cornea) usually present

20. multiple light receiving units, known as ommatidia
SENSE ORGANS
3. Compound Eyes
General
multiple light receiving units, known as ommatidia
each ommatidium usually has its own lens (or cornea)
most have one pair
b. Ommatidia
ommatidium is the individual, self-contained, independent light-detecting unit
15-several thousand in a single compound eye
each includes
>focusing system (cuticular cornea and crystalline cone)
light-transmitting structure (cone stalk)
>light sensitive cells
>screening pigment to isolate (pigment cells)

21. Ommatidia Compound Eye Lens Crystalline cone Pigment cells Facet
Visual cells
Nerve fibers from visual cells
Optic nerve
Ommatidia

22. REPRODUCTION
1. General
most arthropods are gonochoric
fertilization may be external or internal in aquatic arthropods
always internal in terrestrial species
2. Sperm Transfer
sperm transfer usually by mating or copulation
females usually store the sperm in a seminal receptacle

23. 3. Spermatophores
a. General
many arthropods transfer sperm in packets
an adaptation for sperm transfer on land
male abandons spermatophore for female to find or may place it in the female gonopore
most insects use copulation
4. Copulation
present in many aquatic arthropods (crustaceans), also in derived terrestrial forms
often with courtship and behavior patterns
anatomical equipment for internal fertilization by copulation
male inserts an intromittent organ into the reproductive tract of the female
deposits sperm or spermatophores into her seminal receptacle

24. Arthropod Development
Zoea
Nauplius
Megalops

25. Symbiosis

26. Camouflage
Decorator Crab
Sponge crab

27. Camouflage: anemone crab

28. coral guard crabs and pocilloporid corals

29. gall crabs and pocilloporid corals

30. scarlet cleaner shrimp

31. sea cucumber crab and sea cucumbers

32. pompom crabs and sea anemones

33. crabs and sea anemones