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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?
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.
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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.
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.
1. to hold food, 2. to catch food, 3,4,5, used to shred food
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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 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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Living Shores: Figure 264
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.
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SOME LOBSTERS ALONG OUR COAST*
WEST COAST ROCK LOBSTER (Jasus lalandii)
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) 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) 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.
* Extract from Fact Sheet – Crustacea 1 by Margo Branch, March
1997.
Did you know?
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.
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HERMIT CRABS These soft-bodied crabs are well known for their
habit of using an empty mollusc shell for a house. They
rarely leave the security of
this ‘borrowed’ home.
Habitat Hermit crabs are found in rock pools and on sandy
beaches.
Description
Bodies are extensively modified.
They have legs and claws very much like those of crabs.
Soft-skinned asymmetrically shaped abdomen makes them vulnerable
when not protected by the shell.
As they grow, hermit crabs have to move into progressively
larger homes. They carefully feel inside the proposed new home
before making a rapid change.
Feeding Most species are scavengers and feed on any dead animals
they can find.
Predators Bigger fish and octopus and other hermit crabs prey
them on.
Did you know?
Did you know Hermit crabs are not true crabs? Their body shape
more closely resembles the lobster.
1 – nipper;; ‘doorstop’ 2, 3 – walking 4, 5 – reduced in
size, grip the mouth of the shell
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CRABS They are the most specialised crustaceans.
Habitat
Some scuttle around rocks, while others hide in rock cavities in
the balanoid zone. Still others are
found swimming in deeper rock pools or under rocks.
Description
Head and thorax covered by a shield-like carapace.
Two stalked eyes.
Abdomen is reduced and tucked beneath the carapace. Abdomen of
female much broader. Holds the
eggs when in ‘berry’.
The tail fan has disappeared completely.
The first pair of walking legs bears nippers; the remaining four
pairs are used for walking.
Crabs scuttle sideways.
In swimming crabs the back limbs have flattened ends to use as
flippers for swimming and to flick over their backs when they
settle.
Feeding
Some feed on seaweed. Others are ferocious
predators and feed on fish, molluscs and other
small animals.
Predators
Octopus, reef fish, catsharks, eels.
http://www.aquarium.co.za/blog/entry/giant_spider_crab_comes_out_of_her_shell/
Did you know?
Sponge crabs hold sponges or ascidians on their backs to give
them added protection.
Decorator crabs cut off pieces of seaweed and plant them on
their backs to provide camouflage.
http://www.aquarium.co.za/blog/entry/giant_spider_crab_comes_out_of_her_shell/
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PHYLUM: BRYOZOA
MOSS OR LACE ANIMALS The name Bryozoa means
‘moss-animals’. There are over 4,000
species. They are not well
known. These moss or lace animals reveal a marvel of
miniature architectures when viewed through a microscope.
Habitat Large stones, flat algae, and mollusc shells can be
encrusted with bryozoa.
Description
All bryozoans form colonies. One single larva settles and then
divides into two which then divides into four and so on until a
large colony exists.
The colony lays down an external skeleton of chitin or lime to
encase each animal in a coffin-like box. (see different shapes on
the right)
The head bears a ring of tentacles, which filter particles from
the water.
Retractor muscles can pull the head rapidly back into its box
for safety and the operculum (or door) closes on it (illustrated
below).
Feeding Bryozoans are filter feeders.
Predators Some species of nudibranchs and sea spiders prey on
them.
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PHYLUM: MOLLUSCA
The word mollusc comes from the Latin mollusc = soft. Although a
hard shell is the hallmark of the molluscs, the phylum contains
many other species with a reduced shell or the shell may be
absent.
CHARACTERISTICS
They are all soft-bodied animals and unsegmented.
All molluscs can be divided into four regions:
o a usually well-developed head with tentacles and eyes (this
has been lost in the bivalves);
o a ventral, muscular foot on which molluscs crawl on hard
surfaces; o a dorsal visceral mass (body mass) in which the
internal organs are concentrated
and
o a mantle consisting of a sheet of tissue which grows over the
visceral mass and secretes the shell.
The shells assume an extraordinary variety in shape and colour.
They may become enclosed in the mantle and become reduced, as in
slugs and squids.
The radula or ribbon tongue (lacking only in bivalves) is a
horny ribbon that bears rows of teeth and is capable of wide
modification for scraping, piercing and seizing.
Between the mantle and the body mass is a hollow space filled
with seawater - the mantle cavity in which the gills are
situated.
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PHYLUM MOLLUSCA
CLASS GASTROPODA BIVALVIA POLYPLACOPHORA CEPHALAPODA Snails
Slugs
Mussels
Oysters
Chitons Octopus
Squid
Cuttlefish
Paper nautilus
Most are shelled.
Some have forsaken and lost their original shells.
Shell consists of two valves. They are hinged together dorsally
and extend down laterally on either side of the body to encase
it.
Shells are split into eight dorsal plates that cover the centre
of the body.
“Foot” modified into eight or ten
long tentacles armed with suckers. Eyes as complex as
those of humans.