Download Phylum Nematoda The Roundworms

Phylum Nematoda
The Roundworms
Phylum Nematoda
(Greek - Nema = Thread and Eidos = form )
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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
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• 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
Ascaris
lumbricoides
• Human Intestinal
Roundworm
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Necator
americanus
• American Hookworm
• Common in So. USA
• Wear shoes!!!!
Wucheria
bancrofti
• 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
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• Global distribution, except
Europe
• Only common in Tropics
• >1,000,000 humans affected
Dracunculus
medinensis
• “The fiery serpent”
or Guinea Worm
• Int. Host
– Aquatic copepod
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Loa loa
• African eyeworm
• Int. host – deer fly
Trichinella
spiralis
• Trichina worm
• Trichinosis
• Very common in
swine
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Enterobius
vermicularis
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Human pinworm
Direct life cycle
Most common human
parasite
Dirofillaria immitis
• Canine
heartworm
• Very common
• Vectormosquito
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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
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Three major Phyla of
Coelomate Protostomes
• Phylum Mollusca
• Phylum Annelida
• Phylum Arthropoda
Phylum Mollusca
Latin 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
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(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
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Marine
Dorsal shell with 8 plates
Ventral foot used for locomotion and to create suction
Reduced cephalization
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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)
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The Bivalves •
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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
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The cephalopods –
squid, octopus, chambered nautilus (with external shell)
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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)
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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
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Earthworm
• Lumbricus terrestris
• Important ecologically in
soil community
• Anatomy of earthworm
– Monoecious
• Reproductive segments
–clitellum
Anatomy of
earthworm
continued
• Setae
• Digestive
system
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Mouth
Anus
Pharynx
Esophagus
Crop
Gizzard
Intestine
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Polychaete worms
• well developed head; many seta
present on parapodia;
• Nereis – polychaete worm or
sandworm and Christmas tree
worms
Leeches
Anterior and posterior
suckers
Ectoparasites
Hirudin - anticoagulant
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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
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• The earliest arthropods are thought to
have been trilobites (extinct)
– Pronounced segmentation but little
differentiation between body segments
Arachnids
• Spiders, scorpions, mites and horseshoe
crabs
• Body divided into two or three tagma
• Six pair of appendages
– Chelicerae
– Pedipalps
– 4 pair of walking legs
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• The horseshoe crab (Limulus)
• Crustaceans
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Shrimp, crabs, crayfish, lobsters and barnacles
Cheilpeds (pinchers)
Biramous appendages
Carapace covers cephalothorax
Swimming appendages – uropod, swimmerets
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– Barnacles
• Myriapods
• millipedes and centipedes
– Two pair of walking legs per segment
– Uniramous appendages
– terrestrial
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centipedes
– one pair of walking legs per segment
– Uniramous appendages
– terrestrial
Hexapods – Insects
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Most diverse class of animals
Six pair of walking legs
Two pair (usually) of wings !!!!
Metamorphic life cycle
– Incomplete metamorphosis
– Complete metamorphosis
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