Bell Pettigrew Museum
of Natural History
Interpretative Panels
Text: Dr Iain Matthews
Design: Steve Smart & Cavan Convery
A University of St Andrews Development Fund Project
School of Biology
http://biology.st-andrews.ac.uk
6:6 Nemertea
P hy l u m
Nemertea
S u b p hy l u m
Super class
Class
The phylum Nemertea contains around 650
species of thread or ribbon-shaped worms.
Nemerteans, the majority of which are marine,
are usually less than 20cm long, although a few
reach several metres in length.
The basic body plan, which is similar to that
of the turbellarian flatworms, is shared by all
species. However they differ from the Platyhelminthes
in three important respects:
1. They posses a through gut.
2. They have closed blood system.
3. They possess an eversible, barbed proboscis,
which is a completely separate structure from
the gut. This proboscis is housed in a cavity
(rhynchocoel) that runs almost the entire
length of the body.
Almost all species are predatory, although a few
species are parasitic, and some species
(e.g. Malacobdella grossa ) are found as commensals
living in the mantle cavity of molluscs.
Reproduction occurs both as asexual fragmentation
and by sexual reproduction. Most species are
gonochoristic, but some terrestrial and freshwater
species are hermaphrodite and capable of selffertilisation.
Body Plan:
• Bilaterally symmetrical
• Triploblastic
• Acoelomate, with through gut
• Proboscis, retractable into its own
cavity (rhynchocoel)
• Closed circulatory system
Gut
Endoderm
Mesoderm
Ectoderm
The 900 species are included in 2 classes.
Class: Anopla
In the anoplans , the nervous system is located
within the three-layered body wall musculature.
The proboscis lacks stylets and the gut tends
to be simpler than in enoplan species. The
majority of anoplans are marine and benthic,
but a small number of species occur in freshwater
and several species live in brackish water.
Class: Enopla
The enoplan nervous system is located internally
to the two-layered body wall musculature, and
the more complex proboscis has a central region
containing one or more stylets. Again most
enoplans are marine and benthic, however several
are pelagic, and some species are freshwater or
terrestrial.
Classification
within
Nemertea
Class: Anopla
Order: Palaeonemertea
Order: Heteronemertea
Class: Enopla
Order: Hoplonemertea
Order: Bdellonemertea
See specimen.
Ribbon Worms
The world’s longest animal was a nemertean worm. An
individual of Lineus longissimus was washed ashore on
the West Sands in St Andrews in the 1800s. It measured
180 feet (55 m).
Most nemerteans are carnivores. They find their food by
following scent trails, then catch their prey using a
special structure, the proboscis, which shoots out and
wraps around the prey. In some species the proboscis
injects poisons, while in others it has spiny hooks.
Most nemerteans are either male or female. The
reproductive structures only develop during the breeding
season and then disappear again after mating.
The phylum Nemertea is named after a sea nymph,
Nemertes, from Greek mythology.
The nemertean worm, Tubulanus annulatus is
sometimes called the football jersey worm. It gets the
name because the bright red body with white rings of
living specimens looks like a football strip.