Pseudocoelomates

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Pseudocoelomates

• 2 groups of phyla
• Ecdysozoan
• Lophotrochozoan

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Ecdysozoan Phyla

• Nematoda
• Nematomorpha
• Kinorhyncha
• Loricifera
• Priapulida

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Lophotrochozoan Phyla

• Rotifera
• Acanthocephala
• Gastrotricha
• Entoprocta

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Phylum Nematoda

• Facts
• Pseudoceolom
• 25,000 species
• Parasites of nearly all animals and plants

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Facts, cont.

• Symmetry bilateral, unsegmented, triploblastic
• No circulatory or respiratory system

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Niches

• Free-living in all biomes
• Feed on bacteria, yeasts, fungi, algae
• Predatory nematodes
• Feed on rotifers, tardigrades, annelids, other
  nematodes
• Food source for mites, insects, larvae, fungi

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Characteristics

• Cylindrical shape
• Juveniles shed nonliving cuticle between each of
  4 stages
• Most without cilia or flagella
• Express eutely

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Digestion/Excretion

• Tube-within-a-tube digestive system
• Mouth, muscular pharynx, non-muscular intestine,
  rectum, anus
• Excretion via large gland, no protonephridia
• Lateral excretory canals

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Muscles

• Longitudinal muscles only, no circular
• 4 hypodermal cords
• Contractile and noncontractile portions
• Muscle arm extends to nerve

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Nervous System

• Ring of nerve tissue ganglia around pharynx
• lead to dorsal ventral nerve cords

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Sense Organs

• Sensory papillae
• At head tail
• Amphids on head
• free-living forms
• Phasmids near posterior
• Parasitic forms

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Reproduction/Regeneration

• Most dioecious
• Males smaller than females
• Internal fertilization
• Eggs stored in uterus until deposited

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2 Classes

• Class Secernentea (Phasmida)
• Amphids ventrally coiled or derivative
• 3 esophageal glands
• Some with plasmids
• Free-living or parasitic

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2 Classes, cont.

• Class Adenophorea (Aphasmida)
• Amphids well-developed, pocketlike
• 5 esophageal glands
• No phasmids
• Most free-living

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Importance

• Some pathogenic, most tropical
• Large roundworms
• Hookworms
• Trichina worms
• Pinworms
• Filarial worms

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Large Roundworms

• Ascaris lumbricoides
• In humans
• 64 of people in some areas of SE U.S.
• 1.2 billion people worldwide
• A. megalocephala (horses)
• A. suum (pigs)

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Ascaris

• 200,000 eggs/day in feces
• Eggsextended viability in soil
• Host swallows eggs
• Juveniles hatch
• Enter blood, to lungs
• Coughed up, swallowed
• Mature in intestine

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Hookworms

• Necator americanus
• Anterior end hooked
• Dioecious
• Intestinal blood-suckers
• Anemia

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Hooks Life Cycle

• Adult in intestine
• Eggs pass in feces
• Juveniles hatch in soil
• Live on bacteria
• Burrow through human skin
• Travel in blood to lungs
• Coughed up, swallowed

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Trichina Worm

• Trichinella spiralis
• Trichinosis
• Infect humans, hogs, rats, cats, dogs
• 2.4 U.S. infected
• Heavy infections cause death

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Trichina Life Cycle

• Adult in intestine
• Female produces juveniles
• Penetrate skeletal muscle, encyst
• Eat undercooked meat
• Mature in intestine

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Pinworms

• Most common helminthic parasite in U.S.
• Adults in large intestine and cecum
• Unfertilized eggs yield haploid males
• Fertilized eggs yield diploid females

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Pinworm Life Cycle

• Females migrate to anal region at night lay
  eggs, cause itching
• Scratching contaminates hands and bedclothes
• Eggs infective in 6 hours
• Swallowed, hatch, mature

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Filarial Worms

• 8 species in humans
• Wucheria bancrofti Brugia malayi
• Inflame and block lymphatic system
• Dirofilaria immitis
• Dog heartwormcarried by mosquitoes

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Human Filarial Worms

• Females release microfilariae into blood lymph
• Mosquitoes ingest microfilariae mature
  mosquitoes inject
• Elephantiasis
• River blindness (onchocerciasis)carried by black
  flies

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Phylum Nematomorpha

• Horsehair worms
• Adults free-living
• Resemble nematodes
• Juveniles parasites of arthropods
• Stimulate insects to seek water
• Only emerge from host when near water

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Phylum Kinorhyncha

• 1 mm
• Marine worms
• Cosmopolitan
• Most burrow in mud
• Feed on diatoms
• Cannot swim
• Complete digestive system

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Phylum Loricifera

• Discovered 1983 in spaces between marine gravel
• 10 species
• Wide distribution
• Feed on bacteria???

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Phylum Priapulida

• 15 cm
• Cold water burrowing marine worms (deep ocean)
• Eversible proboscis to capture prey
• 16 species
• Complete digestive system

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Phylogeny

• After deuterostomes diverged from protostomes,
  protostomes split
• Ecdysozoa
• Molt during development
• Lophotrochozoa
• Lophophore feeding
• Trochophore-like larvae

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Adaptive Radiation

• Nematodes the most adaptive
• Surviving suboptimal conditions