Pseudocoelomates

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Pseudocoelomates
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Pseudocoelomates

• Group of phyla with pseudocoel
• false body cavity
• Blastocoel persists between body wall and gut
• becomes pseudocoel (or pseudocoelom)

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Pseudocoelomates

• Development of pseudocoelomate
• Blastula
• Gastrulation
• Mesoderm formation

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Pseudocoelomates

• Pseudocoelomate has muscle (mesoderm) as part of
  body wall
• No muscle (mesoderm) surrounding gut (endoderm).

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Pseudocoelomates

• Cuticle secreted by epidermis
• Chitin
• Molting for growth
• Some recent classifications place
  pseudocoelomates with arthropods

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Pseudocoelomates

• Primarily aquatic or marine, some terrestrial
• Many parasitic
• Mostly very small
• Meiofauna
• Live in spaces between grains of soil, sediments
• Respiratory circulatory systems usually absent
• Related to small size

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Pseudocoelomates

• Phylum Rotifera
• Phylum Nematoda

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Phylum Rotifera

• Usually cone or wine-glass shape
• Ring of cilia around mouth
• Early observers mistook for rotating wheel
• Mastax, jaws of a rotifer

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Phylum Rotifera

• Live in freshwaters, oceans
• Some live on mosses, lichens
• Can be dried and will revive when moistened
• 3-4 years common
• 50 years reported

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Phylum Rotifera

• Usually parthenogenic (exhibit parthenogenesis)
• Asexual reproduction
• Female lays asexual eggs, ? females, ? females,
  generation after generation.
• Copies successful genome exactly
• Favored in stable environment

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Phylum Rotifera

• Usually parthenogenic (exhibit parthenogenesis)
• Sexual alternative
• Females produce some males (when, how ?)
• Males inseminate females, which produce sexual
  eggs
• Offspring more variable
• Some variants survive better than others

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Phylum Nematoda

• Largest pseudocoelomate phylum
• estimated 20,000 species
• Worldwide in all imaginable habitats
• Deep sea to mountain tops
• Glaciers to hot springs
• Feed on all kinds of organic materials

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Phylum NematodaAbundance
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Phylum Nematoda

• Body form worm-like
• Slender, tapered at ends
• Mostly less than 2.5 mm long, 0.1 mm wide

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Phylum Nematoda

• Mouth with 6 (primitive) or 3 lip-lobes
• May have sensory bristles, teeth, etc.

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Phylum Nematoda

• Muscles longitudinal only
• Produces thrashing wiggle
• Normal locomotion through sediments, push against
  solid particles
• Muscle cell extensions to nerves
• No peripheral nerves!

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Phylum Nematoda

• Cell constancy
• Adults of a species have same number of cells
• and same number of cells in each organ
• Caenorhabditis elegans used in genetic,
  developmental biology research
• 959 somatic cells (gametes variable)
• 302 nerve cells
• Development of every adult cell can be traced to
  zygote fate of every embryonic cell can be
  predicted.

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Phylum Nematoda

• Most nematodes free-living in soils, sediments
• Important parts of those ecosystems
• Some agricultural pests
• Some parasites in domestic animals and humans
• 138 species use Homo sapiens as host

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Symbiosis
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Symbiosis

• Mutualism
• Lichen
• Fungus Alga
• Termite
• Insect ciliate protozoans

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Symbiosis

• Commensalism
• Epiphytic plants on tree branches
• Mosses
• Ferns
• Spanish moss other bromeliads
• Many orchids
• Ramora on shark

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Symbiosis

• Parasitism
• Roundworms, Ph. Nematoda
• Ascaris
• Trichinella
• Hookworm
• Canine heartworm, filarial worms
• Flatworms, Ph. Platyhelminthes
• Class Planarians not parasitic
• Class Flukes
• Liver fluke
• Schistosoma
• Class Tapeworms

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Modes of transmission

• Of parasitic nematodes, AND other parasites and
  pathogens
• Ingestion of food
• Ingestion of feces
• Entry through skin
• Transmission by vector

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Parasitic nematodes

• Ingestion of food
• Trichinella spiralis
• Larva encysts in muscles of host
• Passed when host dies, eaten by next host

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Parasitic nematodes

• Ingestion of feces
• Ascaris spp.
• infects 1.5 billion people
• 25 of world population
• Pinworm
• common in children in North America

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Parasitic nematodes

• Entry through skin
• Hookworms
• Human
• Canine

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Parasitic nematodes

• Transmission by vector
• Filarial worms
• Filariasis (Elephantiasis)
• Onchocerca
• river blindness
• Canine heartworm

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Parasitic nematodes

• Transmission by vector
• Filarial worms
• Canine heartworm
• life cycle
• Adult in dog heart,
• Larvae in blood ingested by mosquito,
• Residence in mosquito,
• Bite transfers infective larvae to new canine
  host.

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Herbivorous Plant parasite nematodes

• Most nematodes are free-living.
• Herbivores plant parasites damage crop plants.