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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
10:7 Pentastomida
P hy l u m
Pentastomida
S u b p hy l u m
Super class
Class
The pentastomids, or tongue worms, are a small
phylum of around 100 species of blood-consuming
parasites. The adults of most species parasitize
the pulmonary and nasal cavities of predatory
vertebrates and 90% of species specifically have
reptilian hosts, mainly snakes. The larval stages
have a wider range of hosts including insects
and humans. Adult pentastomids are generally
elongated (measuring 1–20cm in length) and
cylindrical with a soft cuticle containing chitin.
They have a complete digestive system with a
mouth and anus, however they do not posses
a respiratory, excretory or circulatory system.
The body appears segmented , but this is only
superficial, forming distinct annuli or false
segments. The anterior end of the body bears
sensory papillae and five short protuberances.
Four of these are tipped with hooks and are
used for attachment to the host. The mouth
is located on the fifth protuberance, the snout.
The name pentastomid, meaning five mouths,
was erroneously based on the belief that each
of the protuberances had a mouth.
The body, especially in the female, is dominated
Body Plan:
• Bilaterally symmetrical
• Triploblastic
• Protostome
• Haemocoelic cavity with through gut
• Unsegmented with 2 pairs of claw-bearing
legs
• Lack excretory, circulatory or gaseousexchange organs
• Chitonous cuticle forming a soft
exoskeleton
Gut
Endoderm
Body Cavity
Mesoderm
Ectoderm
Exoskeleton
by the reproductive system and after fertilisation,
which is internal, up to 500,000 eggs are released.
The primary larval stage develops within the egg,
prior to release into the host’s respiratory tract.
These are then either sneezed out or swallowed
and passed out in the faeces. When a suitable
intermediate host ingests the primary larval stage,
it hatches, penetrates the intestinal wall and
migrates into the abdominal cavity. After several
moults the larva metamorphoses into a quiescent
nymph. When a determinate host (usually a
snake), eats the intermediate host (usually a fish,
amphibian, reptile or small mammal) the nymph
is released into the digestive tract and then bores
into the lungs where it matures.
Classification
within
Pentastomida
Class: Pentastomata
Order: Cephalobaenida
Order: Porocephalida
See specimen.
Tongue Worms
Adult tongue worms all live as parasites in the respiratory
tract of vertebrates. Most species live in the lungs of
snakes.
For a parasite to survive inside a host it has to stop the
host’s immune system from attacking it. To avoid
detection, pentastomids secrete mucus that has been
found to exactly mimic the secretions found in the lungs
of their host. This means that the host can’t distinguish
the tongue worm from its own lungs.
Tongue worms are rare in humans. However eating raw
goat or sheep can lead to a condition called halzoun
or nasopharyngeal linguatulosis. The symptoms of the
disease, common in Lebanon and Sudan, include a
severe itching sensation in the ears and throat. Coughing
and sneezing can dislodge the nymphs, however if they
are not removed they can cause abscesses of the auditory
canal, paralysis and death.