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Molluscs

Molluscs of the Great Barrier Reef

The Great Barrier Reef is home to over 5000 different species of Molluscs, which include the well known giant clams and triton shells. They are an integral part of the reef, providing a source of food for many of the reef creatures, and in turn helping to control algal growth, as many are herbivorous grazers. They are often multi-coloured, and have a wide range of shapes and sizes, ranging from the simple baler shells to the highly complex designs of the murex shells.

Molluscs are soft bodied animals, and therefore most have a hard shell for protection. Those that don’t, such as nudibranchs (or sea slugs, as they’re commonly known), have poisonous chemicals to deter predators. Many of these nudibranchs are brightly coloured, with lots of red colours dominating (a classical warning colour). The most famous sea slug is the beautiful Spanish dancer, which can grow to 15-20cm.

All molluscs have a head (except bivalves) and a muscular foot, and a membranous material that covers their internal organs called a mantle. It is this structure that produces the building blocks to create the shell around most species. The intricate whorls of a shells’ development can be seen if you find a broken shell when beach combing. Also, the older the shell, the more calcified, and therefore heavier, the shell will be.

Being such a large group of animals, they have evolved many unique ways of surviving. Don’t be seduced by the lovely colours of the cone shell. This is one of the most poisonous creatures on the sea floor. This group feeds primarily on fish, and if you’re a slow moving creature, you’re going to need a virulent toxin to kill your prey quickly. Unfortunately, our evolution has followed the vertebrate path of the fish, and many people have died after been impaled by the tiny harpoon under the snails tongue.

The bivalve group has evolved to another level. The large giant clams have algae in their tissues that photosynthesise, meaning that all they need to do is get nice clear water and plenty of sunshine (2 things we have plenty of on the Great Barrier Reef!) and they will survive quite happily. The giant clams can reach over 1m in length, and up to 300kg in weight. It is weight alone that keeps them on the sea floor.

Another unique group is the cephalopods, which include the squids, octopus and cuttlefish. This group have well developed heads and large eyes, and the remnants of their shells have evolved into an internal structure in some species (the well known cuttlebone that birds love to chew on comes from the cuttlefish). One of the most amazing scenes to see on the reef is when two cuttlefish are going through their courtship routine. The animals have amazing powers over their skin patterns and colours, and the male and female will go through flowing changes, sometime looking like a TV test pattern. When the female is fertilized, she will physically place her eggs into the protection of some branched coral, and stand guard for several days to help ensure their safety.

There are many wonderful molluscs to see on the reef, but remember – all shells are protected on the reef, either alive or dead. Don’t be tempted, as even the dead shells play an important part on the reef. Certain fish will only lay their eggs in dead, broken shells.

Worm

These days, when someone talks about worms, we automatically think of viruses affecting our computers. However, this large and diverse group of invertebrates is an important part of the Great Barrier Reef community, and is often involved in complex relationships with other marine creatures.

The term “worm” applies to a number of different phyla (groups), and they are grouped based on their individual structures. Nematode worms are covered in a flexible outer layer, similar in structure to our fingernails, and completely lack cilia for locomotion. Annelid worms, on the other hand, have a more typical “worm” shape, with a segmented body and a distinct head. The classic Christmas tree or fanworm, is a great example. These polychaetes create a tube made of limestone or grainy particles that increase in length as the worm grow. The 2 fans that they extend into the water column are mucus lined and multi-purposed, in that they collect fine particles to feed on, and also extract oxygen from the water. The colours of these fans range from orange and yellow through to blue and white. When danger approaches, the fans are quickly pulled into the chamber, and a hard cover (called the operculum) is pulled over the top like a trap door.
Bristle worms are free living annelids, and are characterized by a series of hairs or bristles arising from each segment of the worm. Some fishermen might know them as blood worms. Bristle worms feed in a number of ways: some burrowing types feed off the organic material as they move through sediments, whilst other more aggressive types have strong jaws and will attack worms and snails. These amazing creatures, like a lot of other worms, can regenerate their body parts if they lose them, even if their heads get bitten off. Some species, like the fire worm, can cause quite a skin irritation if brushed against human skin.

Flatworms are amongst the prettiest of all worms, coming in colours of deep purple, pink and yellow. The bright colours often mimic the colours of toxic nudibranchs, which helps the worms avoid predation. They range from extremely small (less than 1mm!) to up to a meter in length. Most species are rarely seen, due to the fact they live in the sea floor sediments. Lucky for us, however, most of the really colourful ones are about 2-3cm long, and are regularly seen by reef visitors. Some of the larger flatworms can be seen swimming through the water column, and are often confused with nudibranchs such as the Spanish Dancer.

Many polychaete worms species go through a mass spawning event, much like the corals – it makes good sense to maximize your reproductive potential when large numbers congregate together (kind of like the swinging 60’s!). Many overnight dive boats have observed the appearance of millions of worms gathering around the night lights. Often at this stage, the worms have undergone a drastic change in their morphology, developing organs for swimming and sometimes the development of eyes. The resulting larvae exist in the water column for a period of time before descending to the sea floor to start the cycle all over again.

Green Sea Cucumber on sea floor

Sea Cucumber

These days, when someone talks about worms, we automatically think of viruses affecting our computers. However, this large and diverse group of invertebrates is an important part of the Great Barrier Reef community, and is often involved in complex relationships with other marine creatures.

The term “worm” applies to a number of different phyla (groups), and they are grouped based on their individual structures. Nematode worms are covered in a flexible outer layer, similar in structure to our fingernails, and completely lack cilia for locomotion. Annelid worms, on the other hand, have a more typical “worm” shape, with a segmented body and a distinct head. The classic Christmas tree or fanworm, is a great example. These polychaetes create a tube made of limestone or grainy particles that increase in length as the worm grow. The 2 fans that they extend into the water column are mucus lined and multi-purposed, in that they collect fine particles to feed on, and also extract oxygen from the water. The colours of these fans range from orange and yellow through to blue and white. When danger approaches, the fans are quickly pulled into the chamber, and a hard cover (called the operculum) is pulled over the top like a trap door.
Bristle worms are free living annelids, and are characterized by a series of hairs or bristles arising from each segment of the worm. Some fishermen might know them as blood worms. Bristle worms feed in a number of ways: some burrowing types feed off the organic material as they move through sediments, whilst other more aggressive types have strong jaws and will attack worms and snails. These amazing creatures, like a lot of other worms, can regenerate their body parts if they lose them, even if their heads get bitten off. Some species, like the fire worm, can cause quite a skin irritation if brushed against human skin.

Flatworms are amongst the prettiest of all worms, coming in colours of deep purple, pink and yellow. The bright colours often mimic the colours of toxic nudibranchs, which helps the worms avoid predation. They range from extremely small (less than 1mm!) to up to a meter in length. Most species are rarely seen, due to the fact they live in the sea floor sediments. Lucky for us, however, most of the really colourful ones are about 2-3cm long, and are regularly seen by reef visitors. Some of the larger flatworms can be seen swimming through the water column, and are often confused with nudibranchs such as the Spanish Dancer.

Many polychaete worms species go through a mass spawning event, much like the corals – it makes good sense to maximize your reproductive potential when large numbers congregate together (kind of like the swinging 60’s!). Many overnight dive boats have observed the appearance of millions of worms gathering around the night lights. Often at this stage, the worms have undergone a drastic change in their morphology, developing organs for swimming and sometimes the development of eyes. The resulting larvae exist in the water column for a period of time before descending to the sea floor to start the cycle all over again.

Blue Seaslug

These days, when someone talks about worms, we automatically think of viruses affecting our computers. However, this large and diverse group of invertebrates is an important part of the Great Barrier Reef community, and is often involved in complex relationships with other marine creatures.

The term “worm” applies to a number of different phyla (groups), and they are grouped based on their individual structures. Nematode worms are covered in a flexible outer layer, similar in structure to our fingernails, and completely lack cilia for locomotion. Annelid worms, on the other hand, have a more typical “worm” shape, with a segmented body and a distinct head. The classic Christmas tree or fanworm, is a great example. These polychaetes create a tube made of limestone or grainy particles that increase in length as the worm grow. The 2 fans that they extend into the water column are mucus lined and multi-purposed, in that they collect fine particles to feed on, and also extract oxygen from the water. The colours of these fans range from orange and yellow through to blue and white. When danger approaches, the fans are quickly pulled into the chamber, and a hard cover (called the operculum) is pulled over the top like a trap door.
Bristle worms are free living annelids, and are characterized by a series of hairs or bristles arising from each segment of the worm. Some fishermen might know them as blood worms. Bristle worms feed in a number of ways: some burrowing types feed off the organic material as they move through sediments, whilst other more aggressive types have strong jaws and will attack worms and snails. These amazing creatures, like a lot of other worms, can regenerate their body parts if they lose them, even if their heads get bitten off. Some species, like the fire worm, can cause quite a skin irritation if brushed against human skin.

Flatworms are amongst the prettiest of all worms, coming in colours of deep purple, pink and yellow. The bright colours often mimic the colours of toxic nudibranchs, which helps the worms avoid predation. They range from extremely small (less than 1mm!) to up to a meter in length. Most species are rarely seen, due to the fact they live in the sea floor sediments. Lucky for us, however, most of the really colourful ones are about 2-3cm long, and are regularly seen by reef visitors. Some of the larger flatworms can be seen swimming through the water column, and are often confused with nudibranchs such as the Spanish Dancer.

Many polychaete worms species go through a mass spawning event, much like the corals – it makes good sense to maximize your reproductive potential when large numbers congregate together (kind of like the swinging 60’s!). Many overnight dive boats have observed the appearance of millions of worms gathering around the night lights. Often at this stage, the worms have undergone a drastic change in their morphology, developing organs for swimming and sometimes the development of eyes. The resulting larvae exist in the water column for a period of time before descending to the sea floor to start the cycle all over again.

Plankton

These days, when someone talks about worms, we automatically think of viruses affecting our computers. However, this large and diverse group of invertebrates is an important part of the Great Barrier Reef community, and is often involved in complex relationships with other marine creatures.

The term “worm” applies to a number of different phyla (groups), and they are grouped based on their individual structures. Nematode worms are covered in a flexible outer layer, similar in structure to our fingernails, and completely lack cilia for locomotion. Annelid worms, on the other hand, have a more typical “worm” shape, with a segmented body and a distinct head. The classic Christmas tree or fanworm, is a great example. These polychaetes create a tube made of limestone or grainy particles that increase in length as the worm grow. The 2 fans that they extend into the water column are mucus lined and multi-purposed, in that they collect fine particles to feed on, and also extract oxygen from the water. The colours of these fans range from orange and yellow through to blue and white. When danger approaches, the fans are quickly pulled into the chamber, and a hard cover (called the operculum) is pulled over the top like a trap door.
Bristle worms are free living annelids, and are characterized by a series of hairs or bristles arising from each segment of the worm. Some fishermen might know them as blood worms. Bristle worms feed in a number of ways: some burrowing types feed off the organic material as they move through sediments, whilst other more aggressive types have strong jaws and will attack worms and snails. These amazing creatures, like a lot of other worms, can regenerate their body parts if they lose them, even if their heads get bitten off. Some species, like the fire worm, can cause quite a skin irritation if brushed against human skin.

Flatworms are amongst the prettiest of all worms, coming in colours of deep purple, pink and yellow. The bright colours often mimic the colours of toxic nudibranchs, which helps the worms avoid predation. They range from extremely small (less than 1mm!) to up to a meter in length. Most species are rarely seen, due to the fact they live in the sea floor sediments. Lucky for us, however, most of the really colourful ones are about 2-3cm long, and are regularly seen by reef visitors. Some of the larger flatworms can be seen swimming through the water column, and are often confused with nudibranchs such as the Spanish Dancer.

Many polychaete worms species go through a mass spawning event, much like the corals – it makes good sense to maximize your reproductive potential when large numbers congregate together (kind of like the swinging 60’s!). Many overnight dive boats have observed the appearance of millions of worms gathering around the night lights. Often at this stage, the worms have undergone a drastic change in their morphology, developing organs for swimming and sometimes the development of eyes. The resulting larvae exist in the water column for a period of time before descending to the sea floor to start the cycle all over again.

Red and white shrimp

Crustaceans

These days, when someone talks about worms, we automatically think of viruses affecting our computers. However, this large and diverse group of invertebrates is an important part of the Great Barrier Reef community, and is often involved in complex relationships with other marine creatures.

The term “worm” applies to a number of different phyla (groups), and they are grouped based on their individual structures. Nematode worms are covered in a flexible outer layer, similar in structure to our fingernails, and completely lack cilia for locomotion. Annelid worms, on the other hand, have a more typical “worm” shape, with a segmented body and a distinct head. The classic Christmas tree or fanworm, is a great example. These polychaetes create a tube made of limestone or grainy particles that increase in length as the worm grow. The 2 fans that they extend into the water column are mucus lined and multi-purposed, in that they collect fine particles to feed on, and also extract oxygen from the water. The colours of these fans range from orange and yellow through to blue and white. When danger approaches, the fans are quickly pulled into the chamber, and a hard cover (called the operculum) is pulled over the top like a trap door.
Bristle worms are free living annelids, and are characterized by a series of hairs or bristles arising from each segment of the worm. Some fishermen might know them as blood worms. Bristle worms feed in a number of ways: some burrowing types feed off the organic material as they move through sediments, whilst other more aggressive types have strong jaws and will attack worms and snails. These amazing creatures, like a lot of other worms, can regenerate their body parts if they lose them, even if their heads get bitten off. Some species, like the fire worm, can cause quite a skin irritation if brushed against human skin.

Flatworms are amongst the prettiest of all worms, coming in colours of deep purple, pink and yellow. The bright colours often mimic the colours of toxic nudibranchs, which helps the worms avoid predation. They range from extremely small (less than 1mm!) to up to a meter in length. Most species are rarely seen, due to the fact they live in the sea floor sediments. Lucky for us, however, most of the really colourful ones are about 2-3cm long, and are regularly seen by reef visitors. Some of the larger flatworms can be seen swimming through the water column, and are often confused with nudibranchs such as the Spanish Dancer.

Many polychaete worms species go through a mass spawning event, much like the corals – it makes good sense to maximize your reproductive potential when large numbers congregate together (kind of like the swinging 60’s!). Many overnight dive boats have observed the appearance of millions of worms gathering around the night lights. Often at this stage, the worms have undergone a drastic change in their morphology, developing organs for swimming and sometimes the development of eyes. The resulting larvae exist in the water column for a period of time before descending to the sea floor to start the cycle all over again.