• Makes up 3/4’s of all animal species
  • Includes insects, spiders, scorpions, millipedes, centipedes, crabs, lobsters, & crayfish
  • Arthropod means “jointed foot”
  • Jointed appendages (legs, antenna, mouthparts)
  • Segmented body with paired appendages on each segment)
  • External exoskeleton made of chitin (carbohydrate) & protein for protection & support
  • Exoskeleton has 3 layers — outer waxy layer repels water, middle layer has calcium for extra strength, & inner layer has flexible joints for movement
  • Protostomes (blastopore develops into mouth)
  • Coelomate (mesoderm-lined body cavity)
  • Ventral nervous system
  • Open circulatory system
  • Specialized sensory receptors & high degree of cephalization
  • Have simple or compound eyes & segmented antenna

Movement & Growth

  • Muscles occur in bundles & are attached to inside of exoskeleton on each side of joints
  • Exoskeleton must be periodically molted (shed) for organism to grow
  • Molting called ecdysis
  • Molting hormone released & causes epidermal cells to secrete enzymes that digest & loosen inner exoskeleton
  • New exoskeleton secreted by epidermal cells flexible at first & must harden so arthropod not vulnerable to predators so often stay in hiding after molting
  • Arthropods go through numerous molts

Butterfly Molting Pupal Case

Evolution & Taxonomy

  • Evolved from ancestral arthropod with many body segments each with appendages
  • Modern arthropod segments fused into larger, specialized structures called tagmata
  • Four subphyla
    * Trilobita – extinct trilobites
    * Crustacea – shrimps, lobsters, crayfish, & barnacles
    * Chelicerata – spiders, scorpions, & ticks
    * Uniramia -centipedes, millipedes, & insects

Subphylum Trilobita

  • Includes extinct trilobite
  • Marine
  • Have a head & segmented trunk with one pair of legs on each segment
  • Breathe through gills
  • Single pair of antenna


Subphylum Chelicerata

  • Includes 2 classes — Xiphosura (horseshoe crab) and Arachnida (spiders, ticks, scorpions, & mites)
  • Have a cephalothorax (fused head& thorax) and abdomen
  • No antenna
  • Simple eyes or ocelli
  • Have 6 pairs of jointed appendages:
    * Chelicerae – claws or fangs (1 pair)
    * Pedipalps – used for feeding, walking, sensing, transferring sperm (1 pair)
    * Walking legs – movement (4 pairs)
  • Horseshoe crab
    * Marine
    * Not true crabs
    * Fanglike pincers or chelicerae
    * Use book gills to breathe


  • Arachnids
    * Terrestrial
    * Eight legs
    * Chelicerae or fangs with venom
    * Ocelli
    * No antenna
    * Breathe by book lungs &/or tracheal tubes
  • Spiders
    * Arachnid that feeds on insects (carnivores)
    *  Have oval shaped, unsegmented abdomen
    * Cephalothorax connected by narrow waist to abdomen
    * Have 8 simple eyes or ocelli
    * Fangs pierce prey, inject poison, & suck out body fluids
    * Pedipalps on head help sense prey & move it to the mouth
    * Open circulatory system
    * Ostia are openings in heart where blood reenters
    * Body cavity called hemocoel
    * Hemocycanin is oxygen-carrying pigment in blood
    * Have silk glands to make silk & spinnerets to release silk for webs
    * Breathe by book lungs & tracheal tubes
    * Malpighian tubules filter wastes & reabsorb water


  • Ticks & Mites
    * Parasitic arachnid
    * Fused cephalothorax & abdomen
    * Most abundant arachnid
    * Need blood meal to molt
    * Mites can damage fruit & feed on dead skin at base of hair follicle
    * Ticks carry Lyme disease & Rocky Mountain Spotted Fever





  • Scorpions
    * Have a cephalothorax & long segmented abdomen curled over body
    * Prefer dry regions
    * Poisonous stinger on end of abdomen
    * Breathe through book lungs
    * Pedipalps modified into claws
    * Nocturnal predators


Subphylum Crustacea

  • Marine members include shrimp, lobster, copepods, barnacles, & crabs




  • Terrestrial crustaceans called isopods include pillbugs & sowbugs


  • Freshwater members include crayfish & Daphnia (water fleas)


  • All have jaws are mandibles for chewing or tearing
  • Known as mandibulates
  • Have cephalothorax & abdomen
  • Have 10 pairs of jointed appendages
  • Breathe through gills
  • Barnacles
    * Marine
    * Sessile crustaceans that live in limestone case
    * Filter plankton with 12 appendages called cirri


  • Isopods (pillbugs & sowbugs)
    * Live on land in dark places
    * Have 7 pairs of legs on a segmented body
    * Can roll into a ball for protection
  • Crayfish
    * Cephalothorax made of 13 fused segments & covered by protective carapace
    * Antennules located on head help in balance, touch, & taste
    * Statocysts – balancing organs at the base of antennules
    * Antenna on head used for touch & taste
    * Maxillae – paired mouthparts that move side to side to tear food
    * Maxillipeds – help hold food
    * Chelipeds – claws used to capture food & for protection
    * Mandibles – jaws that move up & down to crush  food
    * Walking legs – 8 pairs used for movement
    * Swimmerets – under abdomen to swim, gas exchange, & protect eggs/young
    * Abdomen ends in flat segment called telson with flat uropods on each side


               * Compound eyes on stalks
* Chitinous teeth in stomach grind food
* Wastes leave through anus
*  Green glands filter wastes from blood & help with salt balance
*  Open circulatory system with heart to pump blood to gills & body cells
* Ostia – one way valves allowing blood from dorsal sinus to reenter heart
* Gills attached to walking legs
* Separate sexes that mate in fall & sperm stored in seminal receptacle
*  Eggs attach to swimmerets of female & hatch in several weeks

  • Copepods
    * Largest group of crustaceans
    *  Make up most of the marine plankton
    *  Serve as food for many marine animals
    *  Found in freshwater, marine, & moist terrestrial environments


Subphylum Uniramia

  • All have antenna, mandibles (jaws), & unbranched appendages
  • Includes 3 classes — Chilopoda (centipedes), Diplopoda (millipedes), & Insecta
  • Known as myriapods
  • Most are terrestrial
  • Exoskeleton prevents desiccation (water loss)

Class Chilopoda

  • Terrestrial centipedes
  • Flattened body with longer legs for fast movement
  • Have 1 pair of legs per body segment
  • Predators
  • Mandibles & maxilla for chewing prey (insects & earthworms)
  • Claw-like appendages or pincers on 1st body segment that can inject venom
  • Can coil up for defense


Class Diplopoda

  • Terrestrial millipedes
  • Have 2 pairs of legs per body segment
  • Rounded body
  • Scavengers on decaying vegetation as they burrow through soil
  • Roll into ball when threatened & spray noxious chemical containing cyanide



Segmented Worms
All Materials © Cmassengale

Phylum Annelida

  • Includes duster worms, earthworms, & leeches
  • Abundant in all habitats
  • Have a true coelom fully lined with mesoderm
  • Body divided into external segments called metameres (metamerism)

  • Metameres correspond to internal segments
  • Have a one-way digestive system with a mouth & anus
  • Well developed brain & sensory organs
  • Fluid-filled coelom provides hydrostatic skeleton
  • Most have external bristles or setae that aid movement
  • Setae may be modified into flashy appendages called parapodia


  • Includes 3 classes based on number of setae & presence or absence of parapodia
  • Classes of segmented worms — Oligochaeta, Polychaeta, & Hirudenia

Class Oligochaeta

  • Have no parapodia & few setae
  • Includes earthworms


  •  Bodies may have over 100 metameres
  • Internal partitions called septa
  • Distinct anterior & posterior ends
  • Cephalization (head with sense organs) shows specialization for burrowing
  • Have both circular & longitudinal muscles for movement
  • Have external, saddle-shaped structure called clitellum that forms a cocoon containing eggs & sperm
  • Prostomium or lip digs through soil as earthworm feeds on organic matter
  • Pharynx is a muscular organ behind the mouth to help suck in food
  • Food temporarily stored in crop, ground in gizzard, and digested & absorbed in intestine
  • Wastes called castings pass out through anus
  • Closed circulatory system with 5 pairs of aortic arches or hearts
  • Dorsal blood vessel carries blood posteriorly to cells & ventral blood vessel returns blood anteriorly

  • Secrete mucus to keep skin moist so oxygen will dissolve & diffuse into body
  • Long tubules called nephridia filter wastes from blood & excrete it through pores
  • Simple brain, no eyes, & dorsal and ventral nerve cords
  • Sensitive to light, touch, moisture, chemicals, temperature, & vibrations
  • Hermaphrodites exchange sperm & cross-fertilize
  • Sperm sacs store the worm’s own sperm & seminal receptacles store exchanged sperm

Class Hirudenia

  • No setae or parapodia
  • Includes leeches
  • Have anterior & posterior suckers for attachment


  • Some suck blood from hosts, while others are scavengers or predators
  • Mouth’s of blood-sucking leeches with chitinous teeth & secrete anticoagulant
  • Found in freshwater
  • Flattened dorso-ventrally
  • Hermaphrodites that cross-fertilize

Class Polychaeta

  • Marine
  • Includes sandworms & clamworms
  • Have paddle-like parapodia to move
  • Take in oxygen through parapodia
  • Some are free-swimming predators with strong jaws to feed on small animals
  • Many live commensally with sponges, mollusks, & echinoderms
  • Well-developed head with antenna & specialized mouthparts


Sponge Coloring Diagram and Questions

Found at the Biology Corner                Name __________________ Period ______

SciSponge.bmp (79782 bytes)Sponges – A Coloring Worksheet

Since sponges look like plants, it is understandable why early biologists thought they were plants. Today, we know that sponges are simple, multicellular animals in the Kingdom Animalia, Phylum Porifera. This phylum is thought to represent the transition from unicellular animals to multicellular animals. Most (but not all) sponges are asymmetrical and have no definite shape. Sponges, like all animals, are eukaryotic – meaning their cells have a nucleus. Porifera in Latin means “pore-bearer” and refers to the many pores or openings in these animals. Because of these pores, a sponge can soak up and release water. At one time, real sponges were used for cleaning and bathing. Today, most are artificially made.

All adult sponges are sessile, meaning they are attached to some surface. Since they cannot move, sponges cannot pursue their food. Instead, they are filter feeders, meaning they obtain their food by straining the water for small bits of food like bacteria, algae or protozoans.

Sponges exhibit less specialization (adaptation of a cell for a particular function) of cells than most invertebrates. The primitive structure of a sponge consists of only two layers of cells separated by a non-living jelly like substance. The outer layer of the sponge is the epidermis which is made of flat cells called epithelial cells. Color all the epithelial cells (B) of the epidermis peach or pink.

The inner layer consists of collar cells (A) whose function is to circulate water through the sponge. They do this by swishing their flagella which pulls water through the incurrent pore – water then travels out the osculum at the top of the sponge. As water passes through the sponge in this way, cells absorb food and oxygen and waste is excreted. Color the osculum (D) dark blue, the incurrent pores (C) light blue. Color the inside of the sponge where water circulates the same light blue as you colored the incurrent pores. Color all the collar cells (A) red.

In the jelly-like substance between the epidermis and the collar cells are cells called amebocytes – because they look like amebas. The job of the amebocytes is to travel around distributing food and oxygen to the cells of the epidermis. Because of the amebocytes, scientists believe that sponges evolved from protists. Color all of the amebocytes (E) green – look for them carefully.

The body of the sponge would collapse if it did not have some type of supporting structure. Some sponges have a soft network of protein fibers called spongin. Others have tiny, hard particles called spicules. Many of these spicules also stick out of the epidermis and provide the sponge with protection. Most sponges have a combination of spicules and spongin, the ratio often determines how soft or hard the sponge is. Search for and color all the pointy spicules (F) brown.


Reproduction for sponges can be accomplished both sexually and asexually. There are three ways for a sponge to reproduce asexually: budding, gemmules, and regeneration. Sponges can simply reproduce by budding, where a new sponge grows from older ones and eventually break off. Color the adult sponge (J) pink and all the buds (G) you can find red. Sponges can also reproduce by regeneration, where missing body parts are regrown. People who harvest sponges often take advantage of this by breaking off pieces of their catch and throwing them back in the water, to be harvested later. Finally, sponges can reproduce by creating gemmules – which is a group of amebocytes covered by a hard outer covering. Color the gemmule (H) yellow.

Sexual reproduction occurs when one sponge releases sperm into the water. This sperm travels to another sponge and fertilizes its eggs. The larva form will then swim to another location using its flagella where it will grow into an adult sponge. Most sponge species are hermaphrodites, they can produce both eggs and sperm.


1. What did early biologists think sponges were? ______________________

2. Sponges belong to the Kingdom _________________ and the Phylum _______________

3. Sponges are [ unicellular or multicelluar ] and [ prokaryotic or eukaryotic ]

4. What type of symmetry do sponges have? ___________________________________

5. What does it mean to be sessile? ____________________________________

6. How do sponges get their food? ___________________________________

7. Water enters the sponge through the _____________________ and leaves through the

8. What is the job of the amebocyte? ________________________________________

9. What two substances give the sponge support? _________________________________

10. Tiny sponges growing from the main body of the sponge are called _________________

11. What is a gemmule? ___________________________________________________

12. What is a hermaphrodite? ______________________________________________



Label the letters on the diagrams

SciSpongesColoringWSP3.bmp (1403574 bytes)



Label the letters on the diagrams
SciSpongesColoringWSP4.bmp (2585142 bytes)

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