MEER home Marine biology home Table of Contents Index References Links
Phylum Nemertea
(ribbon worms)



Nemertean, from Halstead, 1965.
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.
Baseodiscus mexicanus , a nemertean from the shallow subtidal, Gulf of California, Mexico. Specimen about 0.5 meter long.



References:

Barnes, 1980
Barnes, Calow, and Olive, 1993
Brusca & Brusca, 1990
Halstead, 1965
Meglitsch & Schram, 1991
Top of Page