(ribbon worms)
Nemertean, from Halstead, 1965.
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Phylum Nemertea (ribbon worms) Nemertean, from Halstead, 1965. |
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The phylum Nemertea
(ribbon worms), also known as the phylum Rhyncocoela
, includes two classes,
the Anopla
(unarmed nemerteans
) and the class Enopla
(armed nemerteans
). Most nemerteans
are
predators, but some are scavengers and others are herbivorous
. They are often found in
and among seaweeds, rocks, mussle
and barnacle
beds, or buried in mud, sand, or gravel
substrates. Some
nemerteans
actively track prey by following their chemical trails, - common prey items are
polychaetes
,
snails
, small crustaceans
, and mollusks
. A few species of Nemerteans
are parasitic
.
All Nemerteans
have
a specialized proboscis
that lies inside a hydrostatic chamber (the rhyncocoel
)
which when squeezed by muscular contractions, causes the eversible proboscis
to be rapidly
extended.
The proboscis
is used to capture prey, - in the armed forms it may have piercing barbs
or
stylets
, which may contain a toxin
used to help subdue the prey.
There are only about 900 species of Nemerteans . Most are benthic and live in temperate areas, but there are a few terrestrial and freshwater species. There are also a few fully pelagic species, that drift or swim slowly in the open ocean. They range from less then 1 cm. to almost 60 meters long, but most Nemerteans are a few centimeters to one or a few meters in length. Their length is somewhat difficult to measure precisely because they are often able to stretch their bodies out to several times their contracted length. |
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Baseodiscus mexicanus , a nemertean from the shallow subtidal, Gulf of California, Mexico. Specimen about 0.5 meter long. |
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References: Barnes, 1980 Barnes, Calow, and Olive, 1993 Brusca & Brusca, 1990 Halstead, 1965 Meglitsch & Schram, 1991 |
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