Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 34

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.

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 35

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

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 36

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.

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 37

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.

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 38

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.

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 39

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

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 40

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/

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 41

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.

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 42

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.

Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 43

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.