Topic 10 Nematomorpha

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Nematomorpha
Also known as:
-Gordian Worms
-Horsehair Worms
Biodiversity Institute of Ontario
Onychophora
Tardigrada
Arthropoda
Ecdysozoa
Nematoda
Nematomorpha
Priapulida
Loricifera
Kinorhyncha
Morphology
 Extremely long and thin worms. They are only 1-2 mm
in diameter, but up to 3 feet long
 Known as the horsehair or gordian worms.
 Non-segmented with an indistinct head no wider than
the body.
 Found predominantly in freshwater (with a few marine
exceptions). Adults are free-living but larvae are
parasitic.
Biological Systems
 They are pseudocoelomates and have no specialized
circulatory or respiratory system and also lack
excretory organs
 Have a digestive system that has atrophied and they
absorb soluble nutrients across their body wall.
Life Cycle
 Have both a parasitic stage, and free-living stage
 Four life stages:
 Egg
 Pre-parasitic larva
 Parasitic larva
 Free-living adult
Larva
 Egg laid in water hatches in 15-80 days producing a
swimming larva with an eversible barbed probosicis.
 Larva enters the body cavity of an arthropod host
where it lives for about a year, grows, and undergoes
metamorphosis (many species have two hosts).
Adult
 Once larva has almost reached adult stage, it begins
manipulating the host’s behavior.
 When ready to emerge, the adults manipulate the host
into entering water. The mechanism is unknown.
 The adult bursts from the body cavity of the host,
killing it in the process.
Adults
 Once the adults emerge, they stop feeding and all of
the worm’s energy is directed towards reproduction.
 Nematomorphs reproduce sexually and a female
nematomorph may deposit one million eggs in water..
Different Life Cycles
 Larva  Intermediate host  Definitive Host
 Most common
 Larva  Plant matter  Definitive Host
 Often found in species that live in temporary ponds.
 Larva  Definitive Host
 Least common
Common Life Cycle
http://www.nematomorpha.net/Nematomorphs.html
Distribution
 They are found worldwide and there are about 325
described species, although many more undescribed
species undoubtedly exist.
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