The Pseudocoelomate Body Plan Chapter 11
The Pseudocoelomate Body Plan
Chapter 11
Aschelminths– Any of the seven phyla
grouped together– Rotifera, Kinorhyncha,
Nematoda, Nematomorpha, Acanthocephala, Loricitera, and Priapulida
Aschelminths
Pseudocoelomate Body Plan
•Lack mesentary, organs lie free
•Often fluid-filled or contain a gelantinous substance
•Most have complete tubular digestive tract from mouth to anus which allows for mechanical breakdown of food, digestion, absorption and feces formation
Aschelminths
Most are microscopic (some grow to over a meter) Bilaterally symmetrical Unsegmented Triploblastic Cylindrical in cross section Most are dioecious (reproductive organs are in
separate animals)
Aschelminths Most are microscopic (some grow to over a meter) Most are free-living, some are parasitic Bilaterally symmetrical Unsegmented Triploblastic Cylindrical in cross section Most are dioecious (reproductive organs are in separate
animals) Cuticle present: may bear spines or scales and is useful
for protection and taxonomic identification Molting or ecdysis shed their cuticle
AschelminthsEutely – Same number of cells for each animal and for each given organ
• Ex. Caenorhabditis elegans (a type of nematode) has 959 cells
• Every worm has 80 cells in their pharnyx
Page 176
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Nematode Reproductive Systems
Dioecious
Phylum RotiferaCharacteristics Corona – ciliated organ around
the head used for locomotion and food gathering
0.1 to 3 mm in length Most are freshwater (less than
10% marine)
Phylum Rotifera
Characteristics Cont…•Usually solitary, free swimming animals although there are a few colonial members•Posterior end with toes and adhesive glands•Parthogenesis common, males reduced in this phylum
Phylum Rotifera
External features• Epidermally secreted
cuticle used for protection
– Lorica – thickened cuticle that makes an encasement used for protection and support
– Epidermis is synctial– Head has a mouth,
brain, sensory organs– Foot has 1-2 toes
» Foot has pedal glands
Phylum Rotifera
Body parts–Head (Anterior)
» Corona
» Mouth
» Buccal field
–Trunk» Middle
–Foot» Toes» Adhesive glands
Phylum Rotifera
Digestion• Mastax jaw that grinds
food
Other organsProtonephridia with flame cells
• Functions for osmoregulation
Phylum RotiferaReproduction
• Some perform sexual reproduction (several use parthogenesis)
• Class Seisonida– 2 Species– Marine– Haploid eggs that must be fertilized – Males & females develop equally
• Class Bdelloidea– All females are parthenogenic– Diploid eggs that produce females– No males present
• Class Monogononta– Amictic eggs – diploid eggs– Mictic eggs – haploid eggs, can
become amitic– Sporadic small sized males
Phylum KinorhynchaCharacteristics
• < 1mm in length• Marine environments-
burrow in mud & sand with snouts
• 150 species• Dioecious• Feed on diatom & algae
and organic matter
Phylum Kinorhyncha• Composed of 13 or 14
zonites– Definite units called zonites
– Zonite 1 can retract into zonite 2
– Spines line most zonites» Pair of lateral spines and
one dorsal spine
– Protonephridia in Zonite 11
– Brain and ventral nerve cord with a ganglion in each zonite
Loricifera
Discovered in 1974 Dioecious Have a large brain Little else is known
about them.
Priapulida
Only 9 species All marine worms Found in colder
water Predaceous Fossils date back
to Middle Cambrian.
Enterobius vermicularis
Pin worm 50% of children in US Spread
– Fecal oral route– Airborne
Spends its entire life in humans. Adult worms are in the large intestine in humans. The female migrates to the anus to deposit her eggs. This causes the itching that is the most common symptom. Eggs are then ingested by the host or another human (commonly transmitted in young children who are not very hygienic).
Sticky tape method
Phylum Acanthocephala
Spiny headed worm 2-host parasites
– Must have invertebrate host Spiny protruding proboscis Both circular and longitudinal
muscles
Nutrition Nutrition by
diffusion Proboscis
attaches to host intestine
Cause extensive damage to the intestinal walls
Some forms cause serious discomfort and ill-health to domestic livestock
Characteristics
• Spiny or thorny-headed• All are intestinal parasites of vertebrates
• Common in various fishes (mostly freshwater)• birds (chickens and turkeys) • mammals and a few reptiles and amphibians.
• Typically cylindrical and small (few mm - cm)
• Constant number of cells, which is species specific
The Acanthocephalan BodyClose up of the proboscisClose up of the proboscis
How the How the proboscis proboscis attaches to attaches to the intestinal the intestinal wall.wall.
All images from:All images from:http://www.biosci.ohio-http://www.biosci.ohio-state.edu/~parasite/state.edu/~parasite/acanthocephala.htmlacanthocephala.html
Phylum Nematomorpha
Commonly called horsehair worms or Gordian worms
Up to 1m long, but very slender animals (1-3mm)
Free-living as adults Often find adults in very clean
streams Juveniles are parasitic in
arthropods (beetles, cockroach)
Nematodes
Found everywhere– Soil– Oceans– Polar ice– Hot springs
Parasites of nearly all plant and animal species!
Phylum Nematode
Microscopic to several meters long Feed on organic matter
– Rotting substances to living tissues of other invertebrates, vertebrates and plant.
Phylum Nematode 12,000 species
– 500,000 possible Most abundant animal
(some 5 billion may be in an acre of fertile garden soil)
Cylindrical body Only longitudinal
muscles Noncellular cuticle with
several layers
Phylum Nematode• Some have lips, some have
spines or teeth on those lips
• Sensory organs– Amphids – chemoreceptors
along the cuticle– Phasmids - chemoreceptors
near the anus– Ocelli – eyespots found in
aquatic nematodes
Ascaris lumbricoides
Roundworm of man 1.2 billion people
– Many in southeast US
Females lay 200,000 eggs a day
Unsanitary habits contaminate ground
Moves by thrashing back and forth
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Source: Redrawn From Centers for Disease Control, Atlanta, GA.
Life Cycle of Ascaris Lumbricoides
Nematode-Caused Diseases Roundworms - more than ½ the world's humans Hookworms Trichinosis (Porkworm) Pinworm infestations - extremely common
parasite in the United States Filariasis (elephantiasis) Onchocerciasis (river blindness)
Ascarid Worms (common roundworm) - lives in intestine- eggs are passed out in the feces
Most roundworms infect dogs, but occasionally they find their way into human hosts
Enterobius vermicularis
Pinworms 50% of children in US Spread
– Fecal oral route– airborne
Enterobius vermicularisSpends its entire life in humans. Adult worms are in the large intestine in humans. The female migrates to the anus to deposit her eggs. This causes the itching that is the most common symptom. Eggs are then ingested by the host or another human
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Life Cycle of Enterobius Vermicularis
Source: Redrawn From Centers for Disease Control, Atlanta, GA.
Hookworms
Anterior end hooks Feed on blood Cause anemia Necator americanus Ancylostoma duodenale
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Life Cycle of Necator Americanus
Source: Redrawn From Centers for Disease Control, Atlanta, GA.
Ancylostoma caninum
www.animalplanet.com/s/3336/157?showName=Monsters%20InsideMe&videoEpisode=Worms%20Crawling%20Under%20My%20Skin
Cutaneous Larval Migrans
Hookworms from dogs and cats
Trichinella spiralis Trichina worm: causes
trichinosis cysts within the muscles are
consumed (undercooked food) worm grows in intestine
forms cysts in the muscles of the new host
symptom: terrible pain in muscles
Diagnosis is by muscle biopsy
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Source: (a) Redrawn From Centers for Disease Control, Atlanta, GA. (b) Photo © Steve Miller
Life Cycle of Trichinella Spiralis•Acquired by ingestion of contaminated pork containing the encysted larva.
•The larvae mature into adults in the human digestive tract.
•They sexually reproduce and give birth to live nematodes that migrate throughout the body and become encysted in muscles and other tissue.
•Infects pigs, bears, dogs, cats, rats & humans
Dirofilaria immitis
Dog heart worm
Wuchereria bancrofti Filarial worms- mostly in
tropical regions Infect the lymph vessels
which are responsible for returning fluid to the circulatory system
Obstruct lymph to cause swelling– Elephantiasis
-- usually transmitted by mosquitoes-- causes elephantiasis
Elephantiasis
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Source: Redrawn From Centers for Disease Control, Atlanta, GA.11-13
Life Cycle of Wucheria spp.
Loa loa
Eye worm Can cause
encephalitis
Dracunculus medinesis
Fiery serpent
Necator americanus – hookworm. Adults live in the small intestine and eggs are excreted with feces. They hatch in the soil and the larva can enter a new host by penetrating the skin. The go to the blood and the lungs where they are swallowed and get to the small intestine to mature into an adult. Diagnosis is by finding eggs in the feces. To prevent infection – wear shoes