Phylum NematodaThe Roundworms

Phylum Nematoda(Greek - Nema = Thread and Eidos = form )

• The roundworms• Widespread – aquatic, marine, soil, plant parasites, animal parasites• >25,000 spp.• Pseudocoelomate – muscle tissue only found along external body

wall; not surrounding digestive tract• Bilateral symmetry• Complete digestive system• Cuticle – external covering, shed periodically for protection• Cylindrical and tapered on both ends• Dioecious (most species)• No circulatory system; transport through fluid in pseudocoelom

• Many nematodes are important members of the soil community - decomposers

• Many are important parasites– Plant parasites– Animal parasites (including – Humans!)

• Following images taken from: – http://www.biosci.ohio-state.edu/~parasite/home.html

Ascarislumbricoides

• Human Intestinal Roundworm

Necatoramericanus

• American Hookworm• Common in So. USA• Wear shoes!!!!

Wucheriabancrofti

• Elephantiasis• Life cycle may be

completed in host• Transmission of

disease by vector – mosquito

• Adults live in Lymph nodes and can prevent flow of lymph; blockage and edema

• Global distribution, except Europe

• Only common in Tropics• >1,000,000 humans affected

Dracunculusmedinensis

• “The fiery serpent”or Guinea Worm

• Int. Host– Aquatic copepod

Loa loa• African eyeworm• Int. host – deer fly

Trichinellaspiralis

• Trichina worm• Trichinosis• Very common in

swine

Enterobiusvermicularis

• Human pinworm• Direct life cycle• Most common human

parasite

Dirofillaria immitis

• Canine heartworm

• Very common• Vector-

mosquito

The Coelomate Protostomes

Remember:• Coelomate- body

cavity completely lined with mesoderm tissue

• Protostome – first opening (blastophore) becomes the mouth

• Spiral cleavage• Schizocoelous –

coelom forms from splits in the mesoderm tissue

Three major Phyla of Coelomate Protostomes

• Phylum Mollusca• Phylum Annelida• Phylum Arthropoda

Phylum MolluscaLatin molluscus = soft

• Approx. 93,000 extant spp.• Most are marine, but also some aquatic

and terrestrial forms as well• Major characteristics:

– Soft body protected by dorsal shell (in most) of calcium carbonate

– Most are dioecious

(major characteristics cont.)– Three main body parts:

• Ventral, muscular foot – locomotion• Visceral mass – contains most internal organs• Mantle – fold of tissue that drapes over visceral mass and secretes

shell (if present)– Radula present in many for feeding– All but one group have an open circulatory system

The Chitons

• Marine• Dorsal shell with 8 plates• Ventral foot used for locomotion and to create suction• Reduced cephalization

Gastropods – snails, slugs and nudibranchs

• Marine, aquatic and terrestrial• Body asymmetric (due to torsion during embryonic development to

create a better center of gravity while carrying the heavy shell)• Ventral foot used for locomotion• Shell, if present, coiled or flat (torsion – rotation of visceral mass)

The Bivalves - clams, oysters, mussels and scallops

• Marine and aquatic• Flat shell, opens ventrally; hinged dorsally• Mantle forms incurrent and excurrent siphons (two valves)• Reduced cephalization• Foot for locomotion by digging• Powerful adductor muscles for shell closing

The cephalopods –squid, octopus, chambered nautilus (with external shell)

• Marine • Foot divided into tentacles with suction cups• Active predators; using a modified siphon to provide jet propulsion• Only mollusk with a closed circulatory system (higher metabolic

rates)• ADVANCED NERVOUS SYSTEM – capable of learning and more

complex behaviors (I.e. communication), very well developed sense organs

• Giant squids are the world’s largest invertebrate (>15m in length)

Phylum Annelida(little rings; annulus=ring)

• Evolutionary landmark – metamerism = repetition of body segments

• Metamerism provides the evolutionary opportunity to specialize body segments

• Coelomate protstomes• Bilateral symmetry• Metanephridia for excretion of metabolic wastes and

osmoregulation• Approx 16,500 spp.• Found in all habitats on earth – marine, aquatic,

terrestrial• In general, most annelids are cylindrical “worm-shaped”,

segmented animals

Earthworm

• Lumbricus terrestris• Important ecologically in

soil community• Anatomy of earthworm

– Monoecious • Reproductive segments

–clitellum

Anatomy of earthworm continued

• Setae• Digestive

system– Mouth– Anus– Pharynx– Esophagus– Crop– Gizzard– Intestine

Polychaete worms

• well developed head; many seta present on parapodia; • Nereis – polychaete worm or sandworm and Christmas tree worms

LeechesAnterior and posterior suckersEctoparasitesHirudin - anticoagulant

Phylum Arthropoda(arthros=joint + pod=foot)

• Main characteristics of phylum arthropoda– Coelomate protostomes– Bilateral symmetry– Jointed appendages (legs, antennae, reproductive

appendages, mouth or feeding appendages)– Ectoskeleton (exoskeleton) from ectoderm; must be shed

periodically (molt = ecdysis); made of chitin– Segmented body divided into three regions (tagma = body

division)• Head• Thorax• Abdomen

Phylum Arthropoda(arthros=joint + pod=foot)

• Main characteristics of phylum arthropoda– Open circulatory system– Respiratory organs

• Tracheal tubes – opening called spiracles• Gills• Book lungs

– Very diverse group - > 1,000,000 spp. (mostly insects)

– Most successful animal phyla – colonize all habitats– 2 out of 3 living things on earth is an arthropod

• The earliest arthropods are thought to have been trilobites (extinct)– Pronounced segmentation but little

differentiation between body segments

Chelicerates

• Arachnids– Spiders, scorpions, mites

• Merostomes -horseshoe crabs• Body divided into two or three tagma• Six pair of appendages

– Chelicerae– Pedipalps– 4 pair of walking legs

• The horseshoe crab (Limulus)

• Crustaceans – Shrimp, crabs, crayfish, lobsters and barnacles– Cheilpeds (pinchers)– Biramous appendages– Carapace covers cephalothorax– Swimming appendages – uropod, swimmerets

– Barnacles

• Myriapods• millipedes and centipedes

– Two pair of walking legs per segment– Uniramous appendages– terrestrial

centipedes – one pair of walking legs per segment– Uniramous appendages– terrestrial

Hexapods – Insects• Most diverse class of animals• three pair of walking legs• Two pair (usually) of wings !!!!• Metamorphic life cycle

– Incomplete metamorphosis– Complete metamorphosis