CLASS: CIRRIPEDIA

BARNACLES
They are highly modified crustaceans.
Habitat
Along the shore they live permanently attached to rocks in
the balanoid zone. Can also attach themselves to other solid
substrata, e.g. pier pilings, whales, bottom of ships, flotsam.
Description
 A shield of calcareous plates encloses body.
 The shells of barnacles dot the rocks in the balanoid zone like small grey volcanoes or white
stars.
 At low tide the barnacles seal the opening at the top of the shell with an operculum of four
plates.
Feeding
Filter feeders. When the tide comes in and they are covered with water, they open up their shells
and extend hairy cirri (leg-like structures) to comb food particles from the water.
They catch plankton and suspended organic matter in the water.
Predators
Carnivorous molluscs and reef fish prey upon barnacles.
Did you know?
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34
Goose Barnacles have a flexible
stalk and occur in colonies
attached to floating objects in
the sea.
Acorn barnacles live on ships,
rocks and even whales.
The animal inside the shell is
actually standing on its head.
The balanoid zone (an intertidal
rocky shore zone) gets its name
from a northern hemisphere
barnacle, Balanus sp.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
MANTIS SHRIMPS
Habitat
Live in burrows or in rock and coral crevices. The Cape mantis shrimp is common in Cape Town
where it burrows into the soft sediment.
Description

Massive raptorial second thoracic limbs.

Eyes are large and stalked

A short carapace covers the front half of the thorax.

They have a large segmented abdomen. Down each side are paddles that are used for
swimming.

Many are brightly coloured and defend their territories.
1. to hold food,
2. to catch food,
3,4,5, used to shred food
Feeding

Highly specialised predators

Two functional groups occur:
o Spearers: impale soft-bodied prey such as fish and shrimps.
o Smashers: strike hard animals like crabs and molluscs with the elbow and stun
them.
Predators
Mantis shrimps are eaten by some species of fish, decapods (10-legged Crustacea) and some
species of Molluscs.
Did you know?
The strike force of a ‘smasher’ approaches that of a bullet and
can easily crack the glass of a small aquarium.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
35
PHYLUM: ARTHROPODA
SUBPHYLUM: CRUSTACEA

Isopods (iso = same + podos = foot) are a diverse group of small crustaceans with over
270 species in southern Africa. They include the kelp louse, fish louse - parasitic on fish and the pill
bug Tylos that burrows in sand.

Amphipods (amphi = both + podos = foot) are also a diverse group of crustaceans with
over 300 species occurring in southern African waters. They include beach-hoppers.
Habitat

Isopods: Found in all marine habitats from the intertidal to the deepest sea.

Amphipods: Most crawl or burrow amongst seaweeds or in sediments.
Description
ISOPODA e.g. Beach-lice
SIMILARITIES

No solid exoskeleton

Jointed segments

Two unstalked eyes

Seven pairs of legs.

Certain species eat kelp.

Thoracic brood pouch in
female.
AMPHIPODA e.g. Sand-hoppers
ISOPODA
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DIFFERENCES
AMPHIPODA
Bodies flattened from top to bottom.  Narrow bodies that are flattened from side
to side.
 Shrimp-like creatures.
Legs similar to one another.
 First two pairs of legs generally form
nippers – help with feeding. Remaining five
pairs end in a simple claw.
 Some have a well-developed jumping ability
(e.g. sand hoppers).
Feeding
Certain isopods and amphipods eat kelp. Some feed on detritus, while others filter food particles
from the water.
Predators
Fish, crabs and worms.
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Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
PRAWNS, ROCK LOBSTERS AND CRABS
ROCK LOBSTERS
Popularly called crayfish, they are correctly
termed "spiny lobsters" or "rock lobsters" to
avoid confusion with clawed freshwater
crayfish.
Habitat
They spend the daytime hiding in holes under
rocks. Small spiny rock lobsters may be seen in
rock pools, but they normally stay in deeper
water.
Description

Large, robust crustacean with a long abdomen ending in a well-developed tail-fan.

Thorax and head covered by a single shield or carapace. None of the walking legs end in
nippers.

They have an elaborate life cycle involving 13 larval stages which drift in the sea for nearly a
year before assuming the adult form and settling on the sea floor.
Feeding
Lobsters do scavenge, but seem to prefer
fresh food. They live on mussels, limpets, sea
urchins and scraps of food lying around.
Predators
Young seals, dog sharks, octopus, fish and
humans hunt them.
Living Shores: Figure 264
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
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SOME LOBSTERS ALONG OUR COAST*
WEST COAST ROCK LOBSTER
(Jasus lalandii)
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Body orange-brown.
Tail fan orange, blue and green.
Front carapace has two large spines and smaller projections between the eyes.
Intolerant of low oxygen levels.
They moult once a year, breed after 5 years and live up to 30 years.
Males reach a carapace length of 190 mm and females 140 mm.
Most important commercial species.
SOUTH COAST ROCK LOBSTER
(Palinurus gilchristi)
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Body orange.
Legs and antennae have alternating pinky-orange and white bands.
Broad plate between eyes flanked by two outer horns.
Second most important commercial species.
EAST COAST ROCK LOBSTER
(Panulirus homarus)
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Brown to brick red; orange spines and blue-green markings on the head.
Two sharp horns project forwards between the eyes.
The abdomen has a scalloped groove on each of abdominal segments 2-5.
Readily sheds some of its legs to distract predators. These legs can be re-grown later.
Did you know?
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The South and West Coast rock lobster fisheries are worth about R150 million rand
a year and about 4 000 people are employed in the industry.
Rock lobsters are not farmed, as it is not possible to rear the larvae.
How far rock lobsters can travel –
*
One theory is that larvae are carried
in the currents in a big circle around
the Atlantic Ocean, north to the
equator across to South America,
south down the American coast and
back across the ocean to South
Africa. Many of them also probably
remain and develop off the coast of
South Africa.
Extract from Fact Sheet – Crustacea 1 by Margo Branch, March 1997.
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Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES