Phylum Arthropoda:

Blueprint for SuccessChapter 14 and 15

Characteristics of Arthropods

Modified segmentation – body regions specialized for specific functions (tagmatization).

Chitinous exoskeleton used for support and protection

Paired, jointed appendages Growth accompanied by

molting (ecdysis)

Characteristics of Arthropods

Ventral nervous system Reduced coelom Open circulatory system

where blood is released into tissue spaces (hemocoel)

Complete digestive tract Metamorphosis often

present

Arthropods Successful in almost all habitats on the earth. Most abundant animals – Several million species

identifiedo 30 to 50 million species may yet be undescribed

Triploblastic, protostome development Exhibit bilateral symmetry Four aspects contribute to arthropod success.

o 1. Metamerismo 2. Exoskeletono 3. The Hemocoelo 4. Metamorphosis

Metamerism Segmentation, most evident

externally Each external segment bears a pair

of appendages Body cavity not divided internally Permits the specialization of regions

of the body for specific functions Regional specialization =

Tagmatizationo Body regions (tagmata) specialized for:

feeding, sensory perception, locomotion, visceral functions.

The Exoskeleton External, jointed skeleton which encloses

arthropods Provides support, protection, and prevents water

loss System of levers for muscle attachment and

movement Secreted by epidermal cells

o Epidermis covered by exoskeleton on outside Consists of two layers:

o 1. Epicuticle = outermost, waxy lipoprotein layero 2. Procuticle/Endocuticle = bulky inner layer made of

chitin

The Exoskeleton Hardening of the

procuticle provides armor-like protection

Modifications of the exoskeletono Formation of jointso Sensory receptors

(bristles, lenses, etc)o Gas exchange

Must be periodically shed for growth (ecdysis)

The Exoskeleton Epicuticle and Procuticle:

epicuticle

exocuticle

endocuticle

epidermis

procuticle

The Hemocoel Provides an

internal cavity for the open circulatory system of arthropods

Allows for the exchange of nutrients, wastes, and (sometimes) gases

Metamorphosis Indirect

development, a significant change in physiology as the immature form becomes an adult

Reduces competition between adults and immature stages

Metamorphosis Evolution of arthropods has resulted in an

increasing divergence of body forms, behaviors, and habitats between immature and adult stages.o Ex: Larval crabs feed on plankton, adult crabs prowl

sandy bottoms for live prey.o Ex: Caterpillar feeds on leafy vegetables, adult butterfly

feeds on nectar from flowers.

Subphylum Crustacea Examples:

o Crayfish, crabs, lobster, shrimp, barnacles and copepods.

Two unique characteristics:o 1. Two pairs of antennae o 2. Biramous appendages

Five classes of crustaceans and numerous orderso Class Malacostraca**o Class Maxillopoda**o Class Branchiopodao Class Remipediao Class Cephalocarida

Class Malacostraca “Soft Shell” Largest class of crustaceans:

o crabs, lobsters, crayfish, shrimp, krill, isopods Body divided into two regions

o 1. Cephalothorax (fusion of sensory/feeding and locomotion tagmata)

o 2. Abdomen (a muscular tail)

Class Malacostraca Paired, biramous appendages in both body

regions Appendages on Cephalothorax:

o Pairs 1 and 2 – Antennae (TWO pairs!)o Pairs 3 through 5 – Mouth appendages

• Mandible Pair (Chewing)• Maxillae (Food handling)

o Pairs 6 through 8 – Maxillipeds • Accessory sensory and food handling appendages

o Pairs 9 through 13 – Pereopods (Walking legs)• Cheliped (Pincher-like)

Appendages on Abdomeno Pleopods (Swimmerets)o Telson used

Class Malacostraca

Class Malacostraca

Reproduction All crustaceans are

dioecious Mating occurs after

molting of the female In females, developing

eggs attach to pleopods and are brooded until hatached

In males, pleopods are modified into claspers and used for sperm transfer

Crayfish have direct development

Class Malacostraca

Feeding Predators,

herbivores, scavengers

Foregut includes an enlarged stomach, specialized for grinding

Midgut = “intestine” Short hindgut ends in

anus and used for water and salt regulation

Class MalacostracaGas Exchange &

Circulation Gills in gill chamber

o Between the carapace and body wall

Muscular Heart Dorsal, anterior, and

posterior arteries empty into sinuses of hemocoel

Sensory & Regulation Ventral nervous

system Compound eyes Crayfish: Excretion

organs are called “green glands”

Other crustaceans: maxillary glands

Class Maxillopoda Includes Barnacles

and Copepods Copepods are most

abundant crustaceano Marine and

Freshwater Barnacles are

sessileo Marine onlyo Most monoeciouso Attach to various

substrateso Some are parasitic

Subphylum Hexapoda Most successful

land animals in terms of numbers of species and individuals

Bodies divided into three tagmata

Five pairs of head appendages

Three pairs of legs on thorax

Class Insecta 30 Orders within Class Insecta! Adult Generalized Insect Characterized by:

o Body divided into head, thorax, abdomeno Three pairs of legso Two pairs of wings

Class Insecta Body Plan

Heado Single pair of antennaeo Mouthpartso Compound eyeso 0 to 3 ocelli (simple eyes)

Thoraxo Three segments: prothorax, mesothorax, metathoraxo One pair of legs attaches to each thoracic segmento Pair of wings attach at margin between mesothorax and

metathorax Abdomen

o 10 to 11 abdominal segments

Insect Flight Insects utilize many forms of

locomotion: walk, run, jump, swim, but flight is perhaps the most important

Insects were the first animals to flyo Important from an evolutionary

perspective! Wings most likely evolved from

outgrowths of the thorax which protects the legs

Required thermoregulation Some insects use a synchronous

(direct) flight mechanism which others use an asynchronous (indirect) flight mechanism.

Insect Flight Synchronous (Direct) Flight

o Used by butterflies, dragonflies, and grasshoppers.

o Flight muscles act on wing baseso A single nerve impulse in flight muscles

results in a single wing cycle Asynchronous (Indirect) Flight:

o Used by flies and waspso Flight muscles act on body wallo Changes in shape of the thorax cause wing

movements.o A single nerve impulse results in many

cycles of the wings

Insect Feeding Variations in mouthparts include

specializations for sucking or siphoning plant or animal fluids

Mouthparts:o Labrum- upper liplike

structure, sensory and not derived from paired appendages

o Mandibles- chewing mouthparts

o Maxillae- have cutting surfaces and a sensory palp

o Labium- sensory lower lipo All aid in food handling

Insect Digestive System

Long and straight and consists of the foregut, midgut, and a hindgut.

Foreguto Behind pharynx is a crop that is used for storageo Proventriuculus or gizzard moves food to midgut helps

grind Midgut

o Aids in digestion and absorptiono Gastric cecae increase surface area

Hindguto Primarily involved with reabsorption of water

Insect Gas Exchange Gas exchange with air requires a large surface

area for the diffusion of gaseso Accomplished through highly branched systems of

chitin-lined tubes called tracheae Tracheae open to outside of body through

spiracleso Spiracles can close to prevent water loss

Most insects have ventilating mechanismso Moves air into and out of tracheal systemo Contracting flight muscleso Passive suction (vacuum) draws air ino Abdominal muscle contraction (pump)

Insect Circulation Open circulatory system similar to other

arthropods but blood vessels less well developed Blood carries nutrients, hormones, wastes Blood is not important in gas exchange Most insects are ectotherms, but some generate

heat using flight muscles

Insect Sensory Functions

Ganglion in head region Sense organs specialized for

functioning on land Insects are capable of some learning

have a memoryo Bees recognize flowerlike objectso When bees are rewarded with nectar,

they will choose flowers with that same odor in subsequent trials

Capable of detecting lighto Used in orientation, navigation, feeding,

etc Compound eyes are well developed

in adults