Pseudocoelomate Animals

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Chapter 15
Pseudocoelomate Animals
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Outline

• Intro to pseudocoelomates
• Ecdysozoans
• P. Nematoda (roundworms)
• P. Nematomorpha (horsehair worms)
• P. Loricifera
• P. Kinorhyncha
• P. Priapulida
• Lophotrochozoans
• P. Rotifera (rotifers)
• P. Acanthocephala (rotifers)
• P. Entoprocta (rotifers)

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Intro

• Molecular evidence suggests after deuterostomes
  diverged, protostomes split into Ecdysozoa and
  Lophotrochozoa
• Characteristics of pseudocoelomates
• either ecdysozoan or lophotrochozoan
• bilateral, unsegmented, triploblastic
• 2 cavities
• gut cavity pseudocoel formed from blastocoel
• lack true coelom (peritoneal cavity), not lined
  w/ peritoneum
• body wall (epidermis)/dermis/muscles surrounding
  pseudocoel

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Intro

• complete digestive tract (tube w/i tube)
• lack circulatory/respiratory systems
• reproductive system
• gonads, dioecious, chitinous eggs
• excretory system
• canals/protonephridia
• nervous system
• cerebral ganglia or nerve ring
• ciliated pits/ papillae/bristles/eyespots
• vermiform
• some have cuticle
• secreted by epidermis
• some exhibit eutely

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Intro

• Advantages of pseudocoelom
• ? freedom of mvmt
• space for development/differentiation of
  digestive/reproductive/excretory systems
• simple means of circulatory system
• storage area for wastes
• hydrostatic skeleton

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Ecdysozoa Phyla
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P. Nematoda (Nemata)

• Roundworms
• 25,000 sp. (500,000 sp.?)
• Microscopic ? 1 m
• Live everywhere
• aquatic/terrestrial/marine/freshwater/polar/tropic
  s
• Free-living/not

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P. Nematoda (Nemata) Form/Function

• Characteristics
• cylindrical
• nonliving cuticle
• flexible, noncellular
• secreted by hypodermis
• shed btwn juvenile growth stages
• func. hydrostatic skeleton/protection
• crisscrossing collagen
• elastic but constrains expansion
• eutely
• hydrostatic skeleton
• pseudocoel fluid-filled
• dorsal/ventral hypodermal cords w/ nerves/lateral
  cords
• lack cilia/flagella/protonephridia

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P. Nematoda (Nemata) Form/Function

• Muscles
• longitudinal (no circular), beneath hypodermis
• run in 4 bands, marked by 4 hypodermal cords
• dorsal/ventral hypodermal cords have nerves
• lateral hypodermal cords have excretory canals
• each muscle cells has contractile fibrillar
  portion (spindle) noncontractile sarcoplasmic
  portion (cell body)
• sarcoplasmic extends into pseudocoel, stores
  glycogen
• fibrillar is striated w/ actin/myosin
• muscle arm extends to ventral or dorsal nerve
• Excretory system
• lack protonephridia
• have canal system or
  1 gland
  cell w/ excretory pore

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P. Nematoda (Nemata) Form/Function

• Feeding/digestion
• parasitic/predatory/herbivorous/saprozoic/coprozoi
  c
• mouth ? pharynx ? non-muscular intestine ? rectum
  ? anus
• food sucked into pharynx
• muscles contract, lumen expands
• intestine is 1 cell thick
• food moves posteriorly as new food enters and
  body moves
• defecation occurs via opening anus allowing
  pseudocoelomic pressure to expel poop

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P. Nematoda (Nemata) Form/Function

• Respiration
• aerobic/anaerobic
• Nervous/sensory system
• ring of nerve tissue and ganglia around pharynx
  lead to dorsal and ventral nerve cords
• sensory papillae at head/tail
• amphids pair of sensory
  organs on
  head
• lead into a deep cuticular
  
  pit w/ modified cilia
• phasmids pair of glands/sensory
  structures near
  posterior

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P. Nematoda (Nemata) Form/Function

• Reproduction
• most dioecious w/ ? smaller than ?
• ? has copulatory spicules to hold ? vulva open
  against hydrostatic pressure
• internal fertilization
• eggs stored in uterus until deposited
• cuticular molts btwn juvenile stages

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P. Nematoda Ascaris

• Large roundworm of humans (Ascaris lumbricoides)
• up to 64 of people in some areas of SE US
• 1.2 B affected worldwide
• infection rates highest in children
• ? more heavily infected than ?
• ? lays 200,000 eggs/day
• eggs pass via hosts feces
• embryos develop into infective
  juveniles in 2 wks
• killed by direct sunlight/? temp.
• resistant to dessication/? O2
• eggs remain viable long after fecal
  matter disappears

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P. Nematoda Ascaris

• infection via ingestion of eggs (finger/uncooked
  veggies)
• juveniles hatch, burrow through intestinal wall
  to veins/lymph
• carried through ? to lungs
• break into alveoli and carried up trachea/pharynx
• coughed up/swallowed
• pass to stomach
• mature in intestine after 2 months
• feed on intestinal contents
• may block/perforate intestines
• emerge from anus/throat
• enter eustachian tubes/middle ear

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P. Nematoda Ascaris

• Roundworm in dogs/cats
• Toxocara
• similar life cycle as human roundworm
• juveniles migrate to uterus of pregnant dogs
• puppies infected

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P. Nematoda Necator

• Hookworms (Necator americanus)
• 911 mm
• hook-like curve on anterior end
• dioecious
• large plates in mouth cuts into intestinal mucosa
• then suck hosts blood
• suck more than they digest (anemia)
• eggs pass in feces
• juveniles hatch in soil where they live on
  bacteria
• infective juveniles burrow through skin to blood
• travel in blood to lungs
• coughed up and swallowed
• mature in the intestine
• symptoms
• retarded growth, ? S

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P. Nematoda Trichina

• Trichina worm (Trichinella spiralis)
• tiny
• 2.4 of US
• trichinosis (potentially lethal)
• adults burrow into intestinal mucosa
• ? directly produce juvenile worms
• juveniles penetrate blood vessels/circulate
  throughout body to all
  tissues (live 10-20 yrs)
• penetrate skeletal muscle
• redirecting gene expression of the musculature so
  it loses its striations
• becomes a nurse cell to the parasite
• encyst in muscle
• excyst when poorly cooked meat containing
  encysted juveniles is eaten
• infect humans/hogs/rats/cats/dogs

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P. Nematoda Enterobius

• Pinworms (Enterobius vermicularis)
• most common nematode parasite in the US
• 30 all children, 16 all adults
• causes little disease
• 12 mm
• adults live in large intestine/cecum
• ? migrate to anal region at night/lay eggs
  (Scotch Tape Method)
• itching
• scratching contaminates hands and bedclothes
• eggs develop/become infective w/i 6 hrs at body
  temp.
• ingested, hatch in duodenum, mature in large
  intestine
• haploid ? from unfertilized eggs
• diploid ? come from fertilized eggs
  (haplodiploidy)