Pseudocoelomates

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Pseudocoelomates

• Aschelminths

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Achelminth Phyla

• Gastrotricha
• Rotifera
• Kinorhyncha
• Nematoda
• Nematomorpha
• Acanthocephala
• Loricifera
• Priapulida
• Entoprocta

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Pseudocoelomates

• Define pseudocoelomate.
• formed directly from the cavity of the blastula
• The cavity is small
• Mostly filled with intestine and oviducts or
  testes.

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Gastrotricha

• Microscopic
• Marine and freshwater species
• Common in lakes, ponds and seashore sands

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Rotifera

• Ciliated crown or corona at the anterior end
• Carnivorous or parasitic
• Most common in freshwater environments
• Body structure
• Head has corona
• Trunk has ridged plates and spines
• Foot has toes for attachment.

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Rotifera
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Kinorhyncha

• About 150 species
• Lives in marine sediment
• Uses head as an anchor, pulls body after it.
• Sexes are separate
• Feed on algae and bacteria

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Nematodes

• bilaterally symmetrical
• worm-like
• surrounded by a cuticle secreted by epidermal
  cells
• longitudinal muscles only

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Nervous System - Nematodes

• Simple ring of nervous tissue around pharynx
• dorsal and ventral nerve cords running the length
  of the body

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Nematode Movement

• Contract longitudinal muscles
• High internal pressure causes the body to flex
• Moves by thrashing back and forth
• No cilia or flagella

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Excretory Systems

• Some have specialized cells that excrete
  nitrogenous wastes
• Others have canals
• Others have canals plus specialized cells
• Nematodes do not have flame cells

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Nematode Reproduction

• Most nematodes are dioecious
• Males use special copulatory spines
• The sperm move by pseudopodia, like amoebas

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Nematode Diversity

• Close to 500,000 species
• Some species are generalists
• Others are much more specialized -
• one species of nematode is known only from felt
  coasters placed under beer mugs in a few towns in
  Germany.

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Nematode Lifestyles

• Many free living
• Many also parasitic
• Play critical ecological roles as decomposers and
  predators on microorganisms

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Nematode-Caused Diseases

• Roundworms - more than ½ the world's humans
• Hookworms
• Trichinosis
• Pinworms infestations - extremely common parasite
  in the United States
• can be transmitted from human to human by eggs
  floating in household dust
• Filariasis (elephantiasis)
• Onchocerciasis (river blindness).

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Nematomorpha 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

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Juveniles are Arthropod Parasites
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Acanthocephala - spiny headed worms

• 2-host parasites
• Must have invertebrate host
• Spiny protrusible proboscis
• About 1150 species
• Dioecious
• Both circular and longitudinal muscles

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Acanthocephalans - Nutrition

• Nutrition by diffusion
• Proboscis attaches to host intestine
• Cause extensive damage to the intestinal walls
• Economic importance Some forms cause serious
  discomfort and ill-health to domestic livestock

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Excretion

• Protonephridia lined with flame cells

Reproduction

• Reproductive structures are contained in strange
  ligament sacs.
• In males two testes are contained within this
  sheath.

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Loricifera

• Discovered in 1974
• Dioecious
• Have a large brain
• Little else is known about them.

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Priapulida The Penis Worms

• Only 9 species
• All marine worms
• Found in colder water
• Predaceous
• Fossils date back to Middle Cambrian.

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Entoprocta (Bryozoa)

• Ciliary feeding device - LOPHOPHORE
• Were known as Bryozoa (moss animals)
• 4000 species
• Few gt 0.5 mm long
• All aquatic (marine and freshwater)

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Ectoproct Feeding
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Entoprocta

• Most are colonial
• Lives in secreted exoskeleton (zoecium) that may
  be
• Gelatinous
• Chitinous
• Stiffened with calcium
• Impregnated with sand.
• Some ectoprocts could be mistaken for hydroids
  but their tentacles are ciliated.

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Ectoproct Colony