cowries - two oceans aquarium€¦ · cowries habitat coral reefs and beyond the lowest level of...
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Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 49
Tiger Cowrie
COWRIES
Habitat
Coral reefs and beyond the lowest level of low tide. There are some temperate species in our region on the South coast.
Description
Colourful shiny egg-shaped shells.
Operculum absent.
The cowrie not only protrudes its mouth and tentacles, but also its mantle which extends right over its shell completely obscuring it and giving it the brilliant gloss so prized by shell collectors.
Feeding Most of them browse on sponges.
Predators
Some species of fish.
Did you know?
Until recently, the Fulton’s cowrie, Cyprea fultoni’s, was only found in the stomach of the black musselcraker (Poenskop). As such, it was considered as extremely rare and was the most expensive cowrie in the world.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 50
Did you know?
Some Nudibranchs secrete toxic chemicals and should not be handled.
Others obtain second-hand weapons by using the stinging cells of their prey (jellyfish, bluebottles, hydroids).
Their enemies are mostly man. Humans threaten their habitat through pollution and development of beaches.
SLUGS AND SNAILS (NUDIBRANCHS (naked gills) – slugs)
Habitat
Rocky reefs, to a depth of about 15m.
Description
They are the most beautiful and highly coloured invertebrates. The colour patterns of many warn predators of their unpleasant taste.
Lack a shell but are not entirely defenceless. (see Did You Know?)
A second pair of tentacles (rhinophores) occurs on top of the head.
The mantle cavity and primary gills may be lost.
A plume of secondary gills around the anus.
Feeding They feed on a variety of foods ranging from marine plants, bryozoa, sea anemones, small crustaceans, hydroids, jellyfish and bluebottles.
Predators Nudibranchs are seldom eaten.
BUBBLE SHELLS are very fragile seaslugs with a shell.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 51
Did you know?
One mussel can pump as much as two litres of water every hour.
Because mussels are filter feeders, they can concentrate pollutants and toxins in their flesh. They should not be collected for food if they are near a city.
CLASS: BIVALVIA
CLAMS, MUSSELS AND OYSTERS
Habitat Bivalves have a diversity of habitats. Some are attached to rocks in the lower balanoid zone where the waves break at low tide. Some species burrow into sand or mud.
Description of Black or Brown Mussels
They have streamlined shells made up of two close-fitting halves.
The two shells snap together using a strong ligament and they are very hard to pull apart once closed.
The shells are anchored to the rocks by strong byssus threads.
On the rocks a great many individual mussels group together to form mussel beds.
The largest part of the animal is the gonad (its reproductive organ).
Feeding Filter the water for minute particles of food (plankton).
Predators Many fish with strong jaws feed on them, as well as lobsters, spiny starfish and octopus. The kelp gull also preys on mussels.
CHARACTERISTICS
All species in this class have two shells enclosing the body.
Body compressed from side to side.
They have gills with cilia around the inner edge of the shell to propel water into the shell.
Lack head with tentacles, eyes and ribbon tongue (radula).
They are filter feeders.
Gonad – largest part of
the animal
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 52
Did you know?
Once detached from the rock, it rolls up to protect the softer body parts. This reflex action prevents damage should the chiton be rolled around by the waves.
The giant chiton, Dinoplax gigas serves as excellent bait for white musselcracker.
CLASS: POLYPLACOPHORA
CHITONS
Habitat Some on underside of rocks, others on exposed rock surface and the giant chiton partially or totally buried in sand on flat rocky reefs.
Description
Oval, flattened mollusc.
Eight, overlapping articulated plates along the back which can flex the body over the surface
Plates surrounded by a tough leathery girdle.
Head completely hidden beneath the girdle and lacks eyes in most.
Remainder of the underside – broad muscular foot rimmed with small gills.
Feeding
When active they creep slowly about, rasping encrusting plants or animals from the rock surface with their powerful file-like radula.
Predators Any predator that is able to dislodge them from the rocks, e.g. seabirds, fish, crabs, eats chitons.
Living Shores : fig 297
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES 53
Did you know?
Cephalopods include the largest invertebrates the sea has ever known.
Deep-sea squids may have bodies 6m long with a total length of 25 m.
Squids are fast swimming animals. Can exceed 20 knots (40km/h).
CLASS: CEPHALOPODA
OCTOPUS, SQUID, CUTTLEFISH, PAPER NAUTILUS
Cephalopod means ‘head-footed’ and they are the top of the mollusc evolutionary tree.
CHARACTERISTICS
Head and foot fused.
Head has highly mobile tentacles with suckers.
Most intelligent invertebrates with a well-developed brain.
Capable of learning.
Image forming eyes, equivalent to those of vertebrates.
Complex buoyancy control.
All have powerful beaks shaped much like a parrot’s beak.
Use jet propulsion to escape predators.
They release a black ‘ink’ into the water when fleeing an enemy or predator.