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Transcript
Ph. Nemertea (Ribbon Worms)
Characteristics of the Phylum
Nemertea
• Marine, freshwater, or terrestrial.
• Triploblastic, [probably] coelomate,
bilaterally symmetrical un-segmented
worms.
• Complete digestive tract with anus.
• Protonephridia.
• Unique proboscis apparatus.
• Closed circulatory system.
Diversity of Proboscis.
Nemerteans are
voracious predators
with well-developed
chemical senses
scyphozoan
medusa
fish eggs
Eplectonema feeding on barnacles.
Closed circulatory system,
thought to be homologous
to coelomic cavities.
Malacobdella grossa
Gastrodermis
Gastrodermis
Reproduction
• Asexual and Sexual Reproduction.
• Most species are dioecious, but a few are
protandric or simultaneous
hermaphrodites.
Some produce planktotrophic larvae
Diversity of Nemerteans: About 900
Species
Lineus longissimus reported to reach 30 meters in length, and
suspected to be 60 meters in length when fully stretch-out!
A few species are commensal and/or
parasitic?
• Malacobdella species commensal within the mantle cavity of
bivalve molluscs.
• Do not feed on the host. There is a relationship between
prevalence of infection and number of worms per clam,
increasing with size.
A few species are commensal and/or
parasitic?
• Carcinonemertes species are ecto-parasites (egg
predators) on branchyuran crabs.
• Different species are specific to different body region of
the host crab (predominantly on the gills of female crabs),
but all feed on eggs. Up to 100,000 worms per crab!
Initially worms infect the gills of male and
female crabs.
They form capsules about themselves by
secreting mucus to cement adjacent gill
lamellae together.
When the female crabs become gravid and
ovigerous, the worms migrate to the egg mass.
Here they become mature and deposit their own
ova. The larvae worms either remain amongst the
host eggs and feed, or leave the host.
Some Pelagic Species.
Nectonemertes sp.
Phallonemertes murrayi
FRESHWATER NEMERTEA: THE PROBOSCIS WORMS,
PROSTOMA SP. COLLECTED FROM WISCONSIN.
PROSTOMA SP. NOTE THE SENSORY GROOVE AND 3 PAIRS
OF EYES
X
Big Picture
• This is a poorly studied phylum that
historically was placed among the
acoelomates, later pseudocoelomates, and
now true coelomates.
• In the near future it will probably change
our understanding of invertebrate
evolution and phylogeny.