Phylum ArthropodaPhylum Arthropoda“jointed foot” “jointed foot”

“jointed appendages”“jointed appendages”the arthropodsthe arthropods

Things that creep around on the Things that creep around on the ocean bottom (some don’t really ocean bottom (some don’t really

creep!); also crustaceans creep!); also crustaceans and other stuffand other stuff

General CharacteristicsGeneral Characteristics

– The largest phylum of animals on earth – three out of The largest phylum of animals on earth – three out of four animals on earth are arthropodsfour animals on earth are arthropods

– Include marine barnacles, shrimp and lobsters as well as Include marine barnacles, shrimp and lobsters as well as all insectsall insects

– Have a segmented bodyHave a segmented body– Bilateral symmetryBilateral symmetry– Jointed appendagesJointed appendages– Hard exoskeleton made of chitinHard exoskeleton made of chitin

• Tough and non-livingTough and non-living• Covers all parts of the animalCovers all parts of the animal• Shed when the animal grows – “molting”Shed when the animal grows – “molting”• Limits size of the animal because it becomes too heavy in Limits size of the animal because it becomes too heavy in

larger animals to allow movementlarger animals to allow movement

Feeding and DigestionFeeding and Digestion

• Because of the mandibles and specialized legs, arthropods Because of the mandibles and specialized legs, arthropods have the ability to eat almost anythinghave the ability to eat almost anything

• Fill all niches of ecology – carnivores, filter feeders, Fill all niches of ecology – carnivores, filter feeders, herbivores and parasitesherbivores and parasites

• Many marine species use their mouthparts or legs to filter Many marine species use their mouthparts or legs to filter the waterthe water

• Parasitic crustaceans have their appendages specialized Parasitic crustaceans have their appendages specialized for sticking onto another organismfor sticking onto another organism

• The mouth of these organism have the first real teeth like The mouth of these organism have the first real teeth like structures made of chitinstructures made of chitin

• They have a two chambered stomach connected to They have a two chambered stomach connected to digestive glands which release enzymes to aide in digestive glands which release enzymes to aide in digestiondigestion

• Digestion is extracellular and waste is sent out through Digestion is extracellular and waste is sent out through the anusthe anus

RespirationRespiration

•Arthropods use gills that resemble feathers Arthropods use gills that resemble feathers located just under their exoskeletonlocated just under their exoskeleton

•Movement of the mouthparts keeps water Movement of the mouthparts keeps water moving in a steady stream over the gills moving in a steady stream over the gills

•Land crabs also have gills for respiration – Land crabs also have gills for respiration – the gills are kept wet with body fluids and the gills are kept wet with body fluids and air is passed over the moistened gills for air is passed over the moistened gills for oxygen absorptionoxygen absorption

Behavior and ResponseBehavior and Response

•Crustaceans have a small and simple brainCrustaceans have a small and simple brain

•Most members of this phylum have well Most members of this phylum have well defined sense organsdefined sense organs

– Compound eyes – a bundle of light sensitive units Compound eyes – a bundle of light sensitive units grouped together at the end of a stalk like grouped together at the end of a stalk like antennaeantennae

– Sense of smell – very sensitive to chemicals in Sense of smell – very sensitive to chemicals in waterwater

•Very complex communication is possible Very complex communication is possible between members through movementbetween members through movement

– Used for courtship and territory protectionUsed for courtship and territory protection

ReproductionReproduction

•Separate male and female individualsSeparate male and female individuals

• Internal fertilization occursInternal fertilization occurs

•Females can store sperm for long periods of Females can store sperm for long periods of time before they use it to fertilize their eggstime before they use it to fertilize their eggs

•Females tend to carry the eggs until they Females tend to carry the eggs until they hatchhatch

•The young are larvae that are plankton-like The young are larvae that are plankton-like and very rarely resemble the adults and very rarely resemble the adults

Class TrilobitesClass Trilobites

• Oldest class from Oldest class from which the rest of the which the rest of the phylum evolvedphylum evolved

• Lived in all the Lived in all the ancient seas. Is now ancient seas. Is now the most common the most common fossil. Distinguishes fossil. Distinguishes the areas that were the areas that were occupied by the occupied by the organism organism

• All members of this All members of this class are now extinctclass are now extinct

Class CrustaceansClass Crustaceans

• Specialized for life in the ocean – all members have gills Specialized for life in the ocean – all members have gills for respiration and appendages specialized for swimmingfor respiration and appendages specialized for swimming

• Over 35,000 species existOver 35,000 species exist

• Generally characterized by a hard exoskeleton, two pairs Generally characterized by a hard exoskeleton, two pairs of antennae and mouth parts called mandiblesof antennae and mouth parts called mandibles

• Have two pair of antennae that are specialize for sensing Have two pair of antennae that are specialize for sensing the environmentthe environment

• The mandibles are generally short, heavy and specialized The mandibles are generally short, heavy and specialized for feedingfor feeding

• Vary in size between microscopic plankton to large Vary in size between microscopic plankton to large lobsterslobsters

• Main body plan is a head, thorax (area behind the head) Main body plan is a head, thorax (area behind the head) and abdomen (the tail end of the animal)and abdomen (the tail end of the animal)

Class CrustaceansClass Crustaceans

•Barnacles are part of this class even though Barnacles are part of this class even though they look like mollusksthey look like mollusks

– The legs that stick out of the volcano shaped The legs that stick out of the volcano shaped exoskeleton capture plankton to eatexoskeleton capture plankton to eat

•Shrimp, lobsters and crabs belong to a Shrimp, lobsters and crabs belong to a group called decapods have 10 legsgroup called decapods have 10 legs

– Prized for foodPrized for food– Two pairs of the legs are often specialized into Two pairs of the legs are often specialized into

claws for feeding purposesclaws for feeding purposes– Tend to be scavengersTend to be scavengers

Other ArthropodsOther Arthropods

– Horseshoe crabs – still the same after Horseshoe crabs – still the same after thousands of years, are called living thousands of years, are called living fossilsfossils

– Sea Spiders – resemble land spiders, most Sea Spiders – resemble land spiders, most common in cold waters and large common in cold waters and large

– Insects – have only three pairs of legs as Insects – have only three pairs of legs as adults, not aquatic but worth mentioningadults, not aquatic but worth mentioning•Largest and most diverse group on earth; may Largest and most diverse group on earth; may

be as many as 1-3 million speciesbe as many as 1-3 million species•Can live at the sea’s edge scavenging on Can live at the sea’s edge scavenging on

seaweed and barnaclesseaweed and barnacles