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Birds
| Fish | Invertebrates
Common Invertebrates of the Tidal Thames
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Common Name: Chinese Mitten Crab
Scientific Name: Eriocheir sinensis
Group classification: Class: Crustacea
(crabs, lobsters, shrimp)
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Natural History Notes: The Chinese Mitten
Crab is the only crab found in the freshwater
zone of the Thames. It is not a native UK species,
but came here accidentally from China by boats.
The first report of a Chinese Mitten Crab in the
Thames was in 1935. Recently the population of
these crabs has grown and they are causing a lot
of damage to the river. They cause erosion and
collapse of natural river banks by digging burrows.
There can be as many as 28 burrows per square
meter of river bank. Adult crabs live in freshwater
but migrate to the estuaries to breed. Females
lay their eggs in the sea. The larvae hatch and
began to grow in brackish water. At the last larvae
stage, the young crabs have become medalopas and
move up the river with the high tides. They develop
into tiny 2.5-3.0 mm long crabs in the freshwater
regions of the Thames, where they will remain
until mature. The crab get its name from the large
amount of hairs that grow on its claws, making
the claws look like small mittens.
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Common Name: Flatworms
Scientific Name: Dendrocoelum
lacteum and Polycelis tenuis
Group classification: Phylum: Platyhelminthes
(flatworms)
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Natural History Notes: Flatworms, unlike
the common earthworm, do not have segmented bodies.
Their bodies are smooth, flat and ribbon-like.
They glide along rock surfaces searching for small
insect larvae and dead animal matter to eat. Dendrocoelum
lacteum is milky white while Polycelis
tenuis is brown. Flatworms have distinct squared-off
or arrow shaped heads with large eyespots.
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Common Name: Freshwater shrimp
Scientific Name: Gammarus pulex
Group classification: Class: Crustacea,
Order: Amphipoda
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Natural History Notes: Freshwater shrimp
may look like shrimp but they are actually amphipods.
Amphipods are a group of crustaceans that have
two different kinds of feet, one kind for swimming
the other for grasping (holding). Unlike true
shrimp, freshwater shrimp swim on their sides
and have curved, flattened bodies. You will find
them hiding under stones and in river plants to
avoid getting eaten. Females carry their eggs
in a pouch. When the eggs hatch they look like
miniature shrimp. They use their long antennae
to locate decomposing plants and animals which
they eat. By eating all this dead matter they
help keep the rivers clean. Freshwater shrimp
can only live in fairly clean water with lots
of oxygen. Finding them indicates that the water
is reasonably clean.
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Common Name: Leech
Scientific Name: Erobdella octoculata
Group classification: Phylum: Annelida
(segmented worms), Class: Hirudonae (leeches)
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Natural History Notes: This common leech
is yellowish or deep red-brown to black. Like
other leeches it has two sucks. One is at the
narrower "head" end and can be used
as a "mouth" to attach to its prey,
the other is at the wider posterior end and is
mainly used for clinging to objects like rocks.
Most leeches feed on the blood and body fluids
of their prey, usually fish. This leech, however,
swallows its prey whole. The eggs of leeches are
laid in tiny oval shaped cocoons.
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Common Name: Swan Mussel
Scientific Name: Anodonta sygnea
Group classification: Phylum: Mollusca,
Class: Pelecypoda (two hinged shells)
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Natural History Notes: The Swan mussel
is one of the most common freshwater bivalves
(two shells) in Britain. They bury themselves
in the river gravel and feed by filtering tiny
particles of food (zooplankton) from the water.
They can filter up to 30 litres of water a day!
Female mussels produce up to a million eggs each
year. The larvae hatches from the egg and embeds
itself into the skin of a passing fish where it
grows as a cyst. Once it has developed a shell
it falls off the fish and continues to mature
in the mud of the river bed. Swam mussels can
live to be 15 years old. They are sensitive to
water pollution because they take in so much water
into their bodies each day. Finding them indicates
that the water is fairly clean.
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Want to learn more? You can look up other
common invertebrates of the Thames:
- Jenkin's spire shell snail
- wandering snail
- hog lice
- mayfly nymphs
- dragonfly nymphs
- estuarine prawns
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Birds
| Fish | Invertebrates
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