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Phylum: ATHROPODA (Arthropods) - The largest phylum of animals with approximately 1,000,000
described species. The most successful phylum based on species diversity, distribution, and numbers of
individuals
Divided into four subphyla
1. Trilobites: now extinct
2. Chelicerates: horseshoe crabs, spiders, scorpions, ticks, mites
3. Crustaceans: copepods, crabs, lobsters, shrimps, barnacles
4. Uniramians: centipedes, millipods, insects
1. The Arthropod Exoskeleton ( the cuticle)
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A combination of protein and chitin.
 Thin and flexible in some locations (at joints) and thick and hard in others
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Provides protection and points of attachment for muscles that move the appendages.
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A barrier to water loss
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Supports a body deprived of water's buoyancy. ( allowed various groups to move onto land)
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Disadvantage: restricts growth ; must be shed periodically for growth (ecdysis = molting)
2. Specialization of Segments
 Body segments became more specialized, reduced in number, and grouped together.
 In some lineages this has resulted in a head, thorax, and abdomen regions.
3. Jointed Appendages
 Arthropod appendages are jointed.
 Became specialized for feeding, sensing, locomotion, sperm transfer, and spinning silk.
4. Respiratory Systems
 Tracheal System : Special tubes called tracheas supply oxygen directly to body tissues.
 Spiracles are openings into the tracheal tubes
 This allows high metabolic rates and sustained activity, as in flight.

feathery gills in aquatic species.
 book-lungs in other terrestrial forms (e.g. spiders).
5. Specialized Sensory Structures
 Extensive cephalization with many sensory structures clustered at the anterior end.
 Well developed sense organs: compound eyes, olfactory receptors (smell), and touch receptors
 Antennae -- receptors for smell & touch
 The compound eye -- wide angle of vision; Many individual units allow motion perception
6. Division of Labor in the Life Cycle

Larval stages – immature stages; concentrate on feeding and growth.
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Adults – mature; specialize in dispersal and reproduction.
 Metamorphosis – the process of change from larva to adult
7. Open Circulatory Systems
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Hemolymph leaves the heart through short arteries and passes into the sinuses (open
spaces) which surround the tissues and organs.
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The hemolymph reenters the heart through pores (Ostia) equipped with one-way valves.
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The blood sinuses comprise the hemocoel. Though the hemocoel is the largest body cavity, it
is not part of the coelom.
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The true coelom is reduced in adult arthropods.
The Four Subphyla
1. Trilobites
Early arthropods – were very numerous but became extinct approximately 250 million years ago.
 Had extensive segmentation, but little appendage specialization.
 As evolution continued, the segments tended to fuse and appendages became specialized for a
variety of functions.
2. Chelicerates [ horseshoe crabs, spiders, scorpions, ticks, mites]
 Body segments:an anterior cephalothorax and a posterior abdomen.
 Chelicerates are named for their feeding appendages, the chelicerae ( pincers or fangs)
 Only one marine chelicerate remains, the horse-shoe crab.
 Most modern chelicerates are found on land as members of the Class Arachnida :
spiders, scorpions, ticks and mites

Chelicerate body –
o cephalothorax with six pairs of appendages:
o 1 pair of chelicerae(pincers or fangs to pierce prey)
o 1 pair of pedipalps (used in sensing,feeding, sperm transfer)
o four pairs of walking legs.
Spiders,
 Fang-like chelicerae, with poison glands, are used to attack prey.
 Chelicerae and pedipalps chew the prey while digestive juices are added to the tissues.
(softens the food and the spider sucks up the liquid).
 Gas exchange is by book-lungs (stacked plates in an internal chamber).
~ The structure of the book-lung provides an extensive surface area for exchange.
Spiders weave silken webs to capture prey.
 silk protein is produced as a liquid by abdominal glands and spun into fibers by spinnerets. The
fibers harden on contact with air.
 Web production is an inherited complex behavior.
 Silk fibers are also used for escape, egg covers, and wrapped around food presented to
females during courtship. ( another complex behavior)
Mites
Some mites are free-living, others are serious pests of plants and animals; ticks are notorious bloodsuckers and disease carriers.
3. Uniramians – Centipedes, Millipedes and Insects
All possess one pair of antennae and unbranched (uniramous) appendages.
Probably evolved on land, ( from marine ancestors with exoskeletons)
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Saw-like mandibles instead of claw-like chelicerae.
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One pair of sensory antennae and a pair of compound eyes.
Moved onto land during the Devonian period.
 Able to move into terrestrial habitats partly due to the presence of the exoskeleton.
 In terrestrial habitats, the exoskeleton provided support and prevented desiccation.
 Fossilized burrows of millipede-like arthropods are the oldest ( about 450 million
years) evidence of terrestrial animals.
A. Millipedes.

Worm-like with a large number of walking legs (2 pair per segment).
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Eat decaying leaves and other plant matter.
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Probably among the earliest land animals.
B. Centipedes.
 Each trunk segment has one pair of walking legs.
 Carnivorous;  Poison claws on the most anterior trunk segment are used to paralyze prey
and for defense.
C. The Class Insecta
 has a greater species diversity than all other forms of life combined.
 There are about 26 orders of insects.
 They inhabit terrestrial and freshwater environments, but only a few marine forms exist.
Entomology = The study of insects.
Evolution of Insects
 The oldest insect fossils are from the Devonian period (about 400 million years ago)
 Insects increased in diversity due to the evolution of:
o Flight -- during the Carboniferous and Permian.
o Specialized mouth parts for feeding on new types of Carboniferous plants.
Evolution and Importance of Flight
 Flight is the key to the success of insects
 Enabled them to escape predators, find food and mates, and disperse more easily
 One or two pairs of wings emerge from the dorsal side of the thorax in most species.
 Wings are extensions of the cuticle and not modified appendages.
 May have first evolved to help absorb heat, then developed further for flight.
 May have initially served for gliding, as gills in aquatic forms, or as structures for swimming.
 Dragonflies were among the first to fly and have two coordinated pairs of wings.
Modifications are found in other groups which evolved later.
Insect Anatomy
1. There are three main body segments: head, thorax and abdomen.
2. The Head has: one pair of antennae, one pair of compound eyes, and several pairs of
appendages modified as feeding mouthparts (for chewing or lapping, piercing, sucking )
3. Thorax – has three pairs of walking legs and the wings.
4. Complete digestive system with specialized regions:
 foregut, midgut (digestion and absorption) and hindgut (water reabsorption).
5. Open circulatory system with hemolymph.
6. Excretory organs - Malpighian tubules which are outpocketings of the gut, process
metabolic waste and aid in water retention..
7. Gas exchange -- tracheal system which opens to the outside via spiracles that can open or
close to regulate air and limit water loss.
8. Nervous system  a pair of ventral nerve cords (with segmental ganglia)
 anterior ganglia are fused into a dorsal brain close to the sense organs.
 Show complex behavior which is inherited (e.g. social behavior of bees, ants).
Insect Development - Many insects undergo metamorphosis during their development.
1. Incomplete metamorphosis -- the young resemble adults but are smaller and have different
body proportions. (e.g., in grasshoppers )
2. Complete metamorphosis = Has larval stages (e.g. maggot, grub, caterpillar) which are very
different in appearance from adults.
 Larva eat and grow before becoming adults; Adults mate and reproduce
 Females lay eggs on the appropriate food source for the larval forms.
Reproduction – Separate sexes; usually reproduce sexually with internal fertilization.
 In most, sperm are deposited directly into the female vagina during copulation.
 Inside the female, sperm are stored.
 Most insects produce eggs although some flies are viviparous.
 Many mate only once in a lifetime;stored sperm can fertilize many batches of eggs.
Insects impact terrestrial organisms in a number of ways. They:
 Compete for food or serve as food.
 Serve as disease vectors.
 Pollinate many crops and orchards.
4. Subphylum: Crustaceans ( shrimps, crayfish, crabs, lobsters)
There are more than 40,000 species of crustaceans in marine and fresh waters.
A. Extensive specialization of their appendages.
 Two pairs of antennae
 Three or more pairs of mouthparts including mandibles
 Walking legs on the thorax ; Appendages are present on the abdomen. ( Unlike insects)
 Lost appendages can be regenerated.
B. Physiology
 Gas exchange - diffusion across thin areas of the cuticle (small forms) or by gills (large forms).
 Open circulatory system is present with hemolymph.
 Excretion - Nitrogenous wastes excreted by diffusion across thin areas of the cuticle.
 Salt balance - regulated by a pair of green glands -- on antenna or maxilla
C. Reproduction and Development
 Most have separate sexes; Some males (e.g. lobsters) have a specialized pair of appendages
to transfer sperm to the female's reproductive pore during copulation.
 Most aquatic crustaceans have at least one swimming larval stage.
D. Classes of Crustaceans
1. Decapods - relatively large crustaceans;
 exoskeleton (cuticle) hardened by calcium carbonate; carapace – the portion over the
cephalothorax which forms a shield for the body
 Freshwater crayfish, Marine lobsters, crabs and shrimp, Tropical land crabs.
2. Isopods - mostly small marine crustaceans but include terrestrial sow bugs and pill bugs.
Terrestrial forms live in moist soil and damp areas.
3. Copepods - numerous small marine and freshwater planktonic crustaceans.
4. Barnacles - sessile - parts of their cuticle are hardened into shells of calcium carbonate.
feed by directing suspended particles toward the mouth with specialized appendages.
Deuterostomes - The deuterostome lineage includes echinoderms and chordates
A very diverse group, but share characteristics which indicate their association:
1. radial cleavage
2. enterocoelous coelom formation
3. the blastopore forms the anus.
Phylum: Echinodermata ( Echinoderms: sea stars, sea urchins, sand dollars, etc)
Echinoderms = “spiny skinned” animals
1. Sessile or sedentary marine forms with radial symmetry as adults.
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Internal and external parts radiate from the center, often as five spokes.
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A thin skin covers a hard calcified endoskeleton.
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Most have bumps and spines which serve various functions.
2. The Water vascular system. - A unique feature of Echinoderms
A network of hydraulic canals which branch into extensions called tube feet that function for
locomotion, feeding and gas exchange.
3. Reproduction
Separate sexes (dioecious); sexual reproduction; external fertilization (sea water)

Bilaterally symmetrical larvae metamorphose into radial adults.

Early embryonic development exhibits the characteristics of deuterostomes.
4. About 7,000 species of echinoderms, ALL MARINE. Divided into 6 classes :
Class Asteroidea - Sea stars
 Bilateral as larva; radial symmetry as adults
 have five or more arms extending from a central disc.
 Nerve Cord – Circular ring – radial nerves
 Complete digestive System – Mouth, cardiac & pyloric stomachs; pyloric caecae
 Separate Sexes ; Gonads located in each arm
 Water Vascular System -- Madreporite  stone canal  ring canal  radial canal  ampulla
 tube feet
 Tubefeet on the undersurface of the arms are extended by fluid forced into them by contraction of
their ampulla.
 Suction cups at the end of each tube foot attach to the substratum and muscles in the tube foot
wall contract and shorten the foot.
 Coordinated action of the tube feet allows slow movement and attachment to prey.
 Tube feet on the arms attach to the shells of clams and oysters; wrap around prey and hold tightly
using the tube feet; The muscles of the mollusk fatigue and the shell is pulled open.
 The sea stars evert their stomachs between the shell halves and secrete digestive juices onto the
soft tissues of the mollusk.
 Sea stars have a strong ability to regenerate, although a single arm cannot regenerate an
entire body. Fishermen chopping up sea stars may actually increase their numbers.
Brittle Stars -- differ from sea stars in that they have:
 Smaller central discs than sea stars.
 Longer, more flexible arms than sea stars.
 No suckers on their tube feet.
 Locomotion is by serpentine lashing of flexible arms.
Sea urchins and Sand dollars.
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Sea urchins are spherical in shape while sand dollars are flattened
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Lack arms but have five rows of tube feet present that provide slow movement.
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Complex jaw-like structure around the mouth is used for feeding on seaweeds and other
food.
Sea lilies.
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
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Most sea lilies are sessile, attached to substratum by stalks.
Motile sea lilies use their arms for a crawling form of locomotion
Arms circle the mouth (which points upward) and are used in suspension feeding.
Have exhibited a very conservative evolution; Extant forms are very similar to fossilized
forms from Ordovician period (500 million years ago).
Sea cucumbers – bear little resemblance to other echinoderms.

They lack spines.

The hard endoskeleton is reduced.

The body is elongated in the oral-aboral axis.
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Some do possess five rows of tube feet, a part of the unique water vascular system.
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Some tube feet around the mouth have developed into feeding tentacles.
Sea daisies -- small (less than 1 cm), disc-shaped marine animals.
 Live in deep water.
 Do not possess arms.
 Tube feet are located around the disc margin.
 Water vascular system consists of two concentric ring canals.