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Phylum

ArthropodaBiology 11

What are Arthropods?

� Segmented invertebrates

� Jointed appendages

� Exoskeleton

� Includes the most numerous and diverse animals on Earth

� They are found in virtually every habitat

General Characteristics

� Segmented (like annelids) but the segments are fused into larger body regions.

� Most arthropod segments have paired jointed appendages

� a body extension, such as an antenna or

leg

General Characteristics

� Exoskeleton is made up of protein bound to chitin

� Provides the arthropod with support and

protection.

� With the shell, their size is limited. To grow,

arthropods must shed their exoskeleton

and grow a new one, this is called

MOLTING.

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Exoskeleton

�Composed of chitin

� Helps prevent desiccation (drying out)

� Sometimes have a waxy layer (waterproof)

� Provides support and protection

�Attachment for muscles

� Limits growth (molting)

Evolution & ClassificationThe 3 living subphyla (class) of arthropods are:

� 1. Subphylum Crustacea:

� 2 pairs of antennae

� chewing mouthparts

� legs with claws

� Ex. lobster, crayfish, crab,

barnacles & shrimp

Evolution and Classification

� 2. Subphylum Uniramia:

� chewing mouthparts

� one pair of antennae

and

� no claws on their legs

� Ex. insects, millipedes,

and centipedes

Evolution and Classification

� 3. Subphylum Chelicerata:

� pincer-like

mouthparts

� no antennae

� Ex. spiders, mites,

and scorpions.

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Class Crustacea

Most crustaceans have two body regions:

� 1. Cephalothorax:

� fused head and chest region

� legs and other appendages are attached

� A hard shell called the carapace covers

this

� 2. Abdomen:

� long, narrow tail region

� divided into seven (7) segments.

� A : cephalothorax

� B : tail

� C : 2nd antennae

� D : eyes

� E : rostrum, a projection out over the eyes

� F: pinching claws (chelipeds)

� G: walking legs (peripods)

� H: carapace

� J: is the uropod, or center part of the tail

� K: marks the telsons, or lateral parts of the tail.

� Swimmerets, not shown, are on the underside of the tail

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External Anatomy

(Crustacean):� 1. Antennae:

� 2 pairs

� Used for balance, touch, taste, and other sensory functions

� 2. Mandibles:

� 1 Pair of jaw-like appendages that chew & crush food� Followed by two other pairs of mouthparts called

maxillas that hold food� The second maxilla has a “bailer” to drive a respiratory

current of water over the gills.

� 3. Jaw feet: � called maxillipeds

� these 3 pairs of jaw feet hold & taste food.

External Anatomy

(Crustacean):� 4. Pinching Claws:

� called chelipeds� Located after the jaw feet � pair of large claws used for catching food

and for defense� 5. Walking legs:

� 4 pairs on the last 4 segments of the cephalothorax

� The first two end in small pincers that aid in grasping food

� the last two end in bristles that are used for cleaning the abdomen

External Anatomy

(Crustacean):

� 6. Swimmerets:

� pairs of appendages occur on the first 5

segments of the abdomen

� used for locomotion

� The first pair are hard and trough-like, used

to transfer sperm in males and soft and

unspecialized in females.

� The last segment has the uropods, enlarged

swimmerets, and the telson.

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Respiration

� The gills are attached to the walking legs.

�As the crayfish walks, a current of water is sent over the gills.

� The feathery gills absorb oxygen from the water and give off carbon dioxide.

�When the crayfish isn’t moving, the gill bailersmove water across the gills so respiration can continue.

Digestion

�After the food has been crushed by the mandibles, it passes into the stomach.

� It is ground into small particles by chitonous teeth on the stomach wall.

� The food then moves to the digestive glandwhere nutrients are absorbed into the body.

� Undigested materials pass through the intestine and out the anus.

Excretion

� Solid feces are excreted through the anus.

�At the base of the antennae is the green gland (bladder) which regulates the amount of salt and liquid in the blood.

Reproduction� Most crayfish live short lives, usually less than two years. So, rapid, high-volume reproduction is

important for the continuation of the species.

� Fertilization occurs in spring, with the fertilized eggs being attached to the female swimmerets.

� The 10 to 800 eggs change from dark to

translucent as they develop.

� Eggs hatch in 2 to 20 weeks, depending on water temperature.

� Baby crawfish stay attached to the mother until

shortly after their second molt.

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Nervous system

� The general pattern of the nervous system is like that of annelids (brain, nerve cord).

� The newest sense organ is the compound eyes.

� These are composed of hundreds or

thousands of closely packed lenses.

� These eyes are well suited for detecting motion which is particularly important to an animal that hunts at night and in deep water with very little light.

INSECTSClass Uniramia

General Structure and

Function

�One pair of antennae

�One pair of compound eyes

� Three pairs of mouthparts

�Can have up to three simple eyes

� Three pairs of legs – one pair attached to each of the three segments of the thorax

Digestion

� Food is chewed by the three pairs of mouthparts

� Passes through the esophagus to the crop(moistened)

� Passes to the gizzard (chitonous teeth grind the food into smaller pieces)

� Food pieces move to the midgutwhere nutrients are absorbed

� Undigested waste enters the intestine and leaves through the anus

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Respiration

�Air enters through exterior holes in the exoskeleton called spicules

�Air travels through the trachea - a ladder-like system of air passages

�Air travels to smaller tubes called tracheoles, where the exchange of gases occurs

Malpighian Tubules in Insects

� The insect has an excretory organ, which it shares with arachnids, called the Malpighian Tubules.

� These tubules get rid of metabolic waste and they filter wastes from the body fluids.

� Their function is more similar to a kidney then any excretory organ so far.

� The waste, which is in the form of dry crystals, is then dumped into the intestine and released.

� Producing dry wastes helps the insects conserve water.

Nervous System

�Complex nervous system

� Brain and several ganglia that act as nerve control centers for body sections in which they are located

� Typanum – specialized for hearing

� Is a flat membrane that converts vibrations into sound and passes it on to the brain for a response