Arthropods & Echinoderms

• Characteristics of Arthropods: all share 4 characteristics

(1) A segmented body with specialized parts

-segments include specialized parts, such as wings, antennae, gills, pincers, and claws

-3 main body parts: head, thorax, and abdomen

(2) Jointed Limbs

-gives arthropods their name: “arthro” for

joint, and “pod” for foot

-jointed limbs makes it easier to move

(3) External Skeleton

-made of protein and chitin

-supports body, allows movement

-acts like a suit of armor to protect organs

-also keeps water inside animals’ body so

it can live on land without drying out

(4) Well Developed Nervous System

-receives information from sense organs, including eyes and bristles

-most arthropods have compound eyes, which is made of many identical, light-sensitive units

• Arthropods are classified by the kinds of body parts that they have

• You can tell differences between them by the number of legs, eyes, and antennae that they have

(1) Centipedes and Millipedes

• One pair of antennae, a hard head, and one pair of mandibles (mouthparts that can pierce and chew food)

• Count the number of legs to tell the difference between them!

centipede millipede

(2) Crustaceans– Shrimps, barnacles,

crabs, and lobsters– Live in water– Have gills for

breathing, mandibles for eating, and two compound eyes on the ends of eyestalks

– Unlike all other arthropods, crustaceans have two pairs of antennae

(3) Arachnids– Spiders, scorpions,

mites, and ticks– Two main body parts:

cephalothorax and abdomen

– Most have four pairs of legs and have no antennae

– Instead of mandibles, they have pair of clawlike mouthparts called chelicerae

– Simple eyes

– Few spider bites need medical treatment, but chelicerae of many spiders cannot even pierce human skin

– Spiders kill more insect pests than any other animal

– Ticks are parasites that live off of hosts’ blood

(4) Insects– Make up the

largest group of arthropods

– All have three main body parts, six legs, and two antennae

– Also have two compound eyes and mandibles

– Metamorphosis: a phase in the life cycle of many animals during which a rapid change from the immature form of an organism to the adult form takes place• Complete: four stages (egg, larva, pupa,

and adult), such as a butterfly• Incomplete: three main stages (egg,

nymph, and adult), such as grasshoppers and cockroaches

–Nymph may shed exoskeleton several times (called molting)

Echinoderms• Echinoderms: spiny

invertebrates, such as starfish, sea urchins, and sand dollars

• Endoskeleton: an echinoderm’s internal skeleton, which covers the animal’s skin

• Adult echinoderms have radial symmetry, but they develop from larvae that have bilateral symmetry

**Nervous SystemNervous System– Simple nervous system similar to that of a jellyfish

– Around the mouth, they have a circle of ring fibers called “the nerve ring”

– In sea stars, radial nerve runs from nerve ring to tip of each arm and controls movement

*Water Vascular SystemWater Vascular System– System of canals filled with fluid– Uses water pumps to help animal move, eat,

breathe, and sense its environment

Kinds of Echinoderms

• (1) Brittle Stars and Basket Stars– Long, slim arms and often smaller than sea

stars– Don’t have suckers on tube feet

• (2) Sea Urchins and Sand Dollars– Round and

endoskeleton forms a solid, shell-like structure

– No arms; use tube feet for movement

– Sea urchins feed on algae and sand dollars just bury in sand and eat tiny particles of food

• (3) Sea Lilies and Feather Stars– May have 5 to 200

feathery arms– Arms stretch away

from body and trap small pieces of food

– Sea lilies sit on top of a stalk; feather stars do not have a stalk

• (4) Sea Cucumbers

– Has a soft, leathery body and no arms

– Unlike other echinoderms, sea cucumbers are long and have a wormlike shape

– Move using tube feet

Is that a Fact?!?!?!

• They have the peculiar adaptation of expelling first sticky threads, perhaps to incapacitate predators, and then their internal organs when startled by a potential predator. These organs can then be regrown.

• (5) Sea Stars (starfish)

– Most familiar echinoderm