Marine
Biology
Activity 2
TAXONOMIC
(DICHOTOMOUS)
KEYS
One method of classifying and identifying objects includes using a taxonomic key,
key sometimes called a dichotomous key.
key
A taxonomic key looks at the similarities and differences between objects using a series of
paired statements or a question. The paired statements describe contrasting characteristics
(it is best to use observable, physical characteristics). You choose one statement out of the
pair that happens to be true of the object you are trying to identify. The statement you
choose may ask you to go on to another pair of statements or it may give you the name of the
object. See below for a simple generic example:
example
Does it have a shell or body armour?
No
Yes
Does it have 5 legs?
No
Anemone
Go to a different key
Yes
Does it have tube feet with suckers?
Yes
Star fish
No
Brittle star
Marine Biodiversity and Ecosystem Functioning EU Network of Excellence
Sustainable development, global change and ecosystems
GOCE-CT-2003-505446
Marine
Biology
Activity 2
r
em b e y
m
e
r
u
v it
Do y o e l a s t a c t i a t
d
th
f r o m yo u l o o k e o f
w here a ss i f i ca t i o n t s ?
t he cl l s a n d pl an
a
anim
Here we will have a closer look at a very large collection of animals called Arthropods
(beetles and other creatures with several legs).
All arthropods have a jointed body, a shell and three or more pairs of legs. There are many
different types of arthropods living in the sea. Shrimp, crabs, lobsters, and barnacles are seagoing
arthropods that have a special name called crustaceans which means 'shelled ones' and they
belong to the Phylum Crustacea.
Crustacea
All crustaceans have a number of pairs of legs. Most have feelers, or antennae for touching and
feeling. Some can also smell with their antennae. All crustaceans breathe with gills and most shed
their shells from time to time. For a while the crustacean's body is soft, and can grow. Then its
outer skin becomes hard and is its new shell. Some crustaceans attach themselves head down
onto a rock and never move again - except to wiggle their legs!
NOW IT’S
YOUR TURN!
*
*
*
(Rostrum)
Can you name/identify different crab
species using a taxonomic key?
*
*
First let us get familiar with the
different parts of a crab so you will be
able to use the key
Main parts to identify/highlight
here for students *
*
Marine Biodiversity and Ecosystem Functioning EU Network of Excellence
Sustainable development, global change and ecosystems
GOCE-CT-2003-505446
*
pereopod
Marine
Biology
Have a go at being
a Taxonomist
Activity 2
SPECIES A - Family Corystidae SPECIES B - Family Grapsidae
Corystes cassivelaunus
Eriocheir sinesis
SPECIES C - Family Majidae
SPECIES D - Family Portunidae
Eurynome aspera
Liocarcinus corrugatus
Marine Biodiversity and Ecosystem Functioning EU Network of Excellence
Sustainable development, global change and ecosystems
GOCE-CT-2003-505446
Marine
Biology
Activity 2
SPECIES E - Family Majidae
Macropodia tenuirostris
Answers
SPECIES A __Corystes
__Corystes cassivelaunus___
cassivelaunus___
SPECIES B ___Eriocheir
___Eriocheir sinesis_______
sinesis_______
SPECIES C ___Eurynome
___Eurynome aspera______
aspera______
SPECIES D ___Liocarcinus
___ Liocarcinus corrugatus__
corrugatus__
SPECIES E ___Macropodia
___Macropodia tenuirostris__
tenuirostris__
Marine Biodiversity and Ecosystem Functioning EU Network of Excellence
Sustainable development, global change and ecosystems
GOCE-CT-2003-505446
Marine
Biology
Activity 2
General
information on
the species
SPECIES A - Family Corystidae
Corystes cassivelaunus
Common names - Long-clawed crab, sand crab, helmet crab, masked crab
An intertidal crab found in sandy soft bottoms with a pale mauve or reddish
brown body. The legs are yellowish-white with brown tips.
Dorsal (top) surface of carapace is minutely granulated and the markings sometimes give the impression of a face :-)
SPECIES B - Family Grapsidae
Eriocheir sinesis
Common name - Chinese Mitten crab, big binding crab and Shanghai hairy crab
A medium-sized burrowing crab that is native in the coastal estuaries of eastern
Asia from Korea in the north to the Fujian province of China in the south, but
migrated to Europe and North-America. The crab is greyish-green to dark brown
and legs are lighter. The carapace is almost square with four conspicuous teeth
separated by three curved notches.
Strictly speaking this is a freshwater river crab however it returns to estuaries to
breed.
SPECIES C - Family Majidae
Eurynome aspera
Common names - Strawberry crab, rough crab
An intertidal crab found on the lower shore or sublittoral on hard (stony sand
and shell substrate) and muddy sand. The body and legs are pale red to brown,
sometimes blue-grey, and the tubercles/warts are white or brownish.
Marine Biodiversity and Ecosystem Functioning EU Network of Excellence
Sustainable development, global change and ecosystems
GOCE-CT-2003-505446
Marine
Biology
Activity 2
General
information on
the species
SPECIES D - Family Portunidae
Liocarcinus corrugatus
Common name - Wrinkled swimming crab
An intertidal reddish brown swimming crab found on coarse sand and gravel
beaches, extending to water depths of 100m on marl.
Carapace (body) with numerous strong transverse hairy ridges.
SPECIES E - Family Majidae
Macropodia tenuirostris
Common name - Slender spider crab
A reddish brown crab found on mud to hard substrates (stones and gravel) and in
estuaries and deep water to 300m.
Marine Biodiversity and Ecosystem Functioning EU Network of Excellence
Sustainable development, global change and ecosystems
GOCE-CT-2003-505446