Molluscs

Molluscs are a diverse group of animals which includes octopus, squid, cuttlefish as well as snails, bivalves and chitons. They are important food animals world wide and some of them for eg. oysters are farmed for eating and also for the production of pearls.


Octopus have been found to be extremely clever- for an invertebrate, and can find their way through complex mazes and they constantly surprise scientists who study them. Octopus, squid and cuttlefish can all change their skin colour and texture which helps them hide in plain view from predators (and their prey) and to communicate with other members of their species.









Generally speaking you would expect to find octopus in water but in the above two images it shows one making its way across a rock shelf from a rock pool (that it was stranded in at low tide) to the ocean 25 m or so away. When I moved in close to photograph it it squirted me three times as I moved around it. It hit me with a jet of water and its aim was spot on no matter if I was in front or behind it. The image was taken at Point Sampson in WA.

At the other end of the scale we have the bivalves like this scallop and gastropods(snails). Scallops live on the sea floor and are filter feeders-they feed of tiny microorganisms. The first time I went diving over a scallop bed I was amazed to see the way move. They snap their shells closed and in effect it works like jet propulsion and moves them about .5m and they can repeat it a number of times so they move some distance. Why do they need to move like this? So they can escape the creature that commonly preys on them - seastars. Over long periods of time they have evolved senses to let them know when their predators are near by. This type of scallop is a popular seafood and fished commercially.

The blue dots around the edge of the shell are eyes. Their eyes don't work anywhere near as well as ours but they certainly have a lot of them!

This is a cone shell. There are many different species of cone shells, many of them have distinctive patterns especially those of tropical regions. This one is from Victorian waters.
This family has a surprising method of self defence. They are able to release projectile darts at anything that handles it or attacks it. The darts have barbs on them and carry toxins. They are normally used to disable its prey. Some are much more dangerous than others. Some tropical species have been responsible for deaths of people. This is a Victorian species and is not considered to be extremely dangerous but it is best not to handle any species of cone shell. These creatures feed at night time so it is easy to avoid them.

This is a Pale-headed octopus, they are found in Victorian waters.

Sea snails can be herbivores(feed on algae and plant matter) or carnivores that feed on live prey or as scavengers. Many sea snails are simple algal grazers and are preyed on by other snails that have developed ways of either drilling holes into other snails shells or by forcing open the tiny door(operculum) that many of them have at their opening.

Although no cephalopods(octopus,squid and cuttlefish) live in fresh water there are a number of bivalves and snails that do. Snails have also become land dwellers and world wide there are hundreds of species that have done so.

Australia is home to a couple of species of octopus that are very tiny and very deadly. It is the Blue-ringed octopus. The one in the photo is from Victoria's temperate water and there is also another similar species which lives in the tropics. They are tiny-the size of a golf ball and their bite is painless but they deliver a powerful neurotoxin that can kill in minutes. They can be found in rock pools and may hide in anything that they can fit in - such as shells. As a general rule especially in Australian waters- NEVER put you fingers anywhere where you cant see them and be careful of the things you do pick up to examine. CPR done effectively will keep a victim alive until an ambulance arrives.

This is a cuttlefish, closely related to the octopus but these creatures have an internal shell, the "cuttlebone" which are often found washed up on beaches as they float. They have eight shorter tentacles and two long ones. In the photo below the cuttle is stalking a ghost shrimp, once it gets withing range of its tentacles its lashes out very quickly at its prey retrieving to its' mouth almost too quickly to see. Note the finger like projections above the eyes.

This picture and the two below are of a nudibranch (a type of sea slug). The branch like structure on its back are actually gills and the name nudibranch literally means naked gill. They are often brightly coloured which warns would be predators that they are distasteful or even toxic. Many of them feed on sponges which often contain chemicals or toxins that they then use for their own defence, and these substances help give them the bright colours and patterns. This one is found in Victorian waters, but most members of this family live in tropical water.

This is a nudibranch from tropical waters around Low Isles in Qld.

Occasionally clusters of eggs like these are washed up on the beach with seaweed. It is an egg mass laid by multiple squid. Squid are similar to cuttle fish but they have no "cuttlebone". The tend to live in open ocean and move quickly.The picture below is of a juvenile squid that hatches from these eggs.

The shells in this picture are neither snails or bivalves. In the middle the creature that looks kind of like a slater is a chiton, a mollusc with eight valves (or plates) They suck firmly onto rocks and feed on encrusting growths(both plant and animal). They are more active, albeit very slowly, at night and they tend to hide under rocks and in crevices. If caught out in the open fish like wrasse will soon pick them off and eat them. Some species have light sensitive spots so they can tell when its night and day. The other shells in the picture are not molluscs at all, they are crustaceans-barnacles and are related to crabs.

This type of bivalve is only found in the tropics(above and below). It is a giant clam and they can grow to be some of the largest shells. These two are at Low Isles. The top one is about 600mm across and the bottom one is much smaller and is a Burrowing clam around 200mm. The largest species in this family may be a metre wide.

Below are some of the common seasnails in Victoria.

This is a pheasant snail, it is popular with collectors because of its pretty markings. Urqharts Bluff, Vic.

Sea snail, Urqharts Bluff, Vic.

Sea snail, Queenscliff, Vic.

These are cowrie shells found along Victorias coast.

Sea snails on Neptunes Necklance, Anglesea, Vic.

These are turbos or warreners, they are common along Victorias rocky shores. These are an edible species and in the past were a food source for aboriginal people of the area.

There are many types of sea snail each with its own particular preferences for food and where they live. Those creatures that are intertidal have to contend with very varied conditions especially on the southern coast. They need to be able to cope with being in water and out of water for extended periods, they need to be able to handle both very hot and cold conditons, drying wind, and even fresh water when it rains and pools around them.

Nerites.

Limpet shells, Vic. Limpets are well designed for intertidal areas. Their muscular foot acts like a really strong suction cup and holds them to the rocks which they live on and their conical shape allows even really rough waves to wash over them without dislodging them.

Depressions in rocks become micro habitat areas for these creatures to congregate. It stays more moist and is out of the way of drying wind.

These are Blue Periwinkles, they live higher up the beach than most other seanails and some even live up to 10m further up the beach than high tide mark.

This is a selection of shells from Urqharts Bluff, Vic. a rocky area of a surf beach. It is quite a diverse collection and were all in the bottom of a small rock pool. The black surface they are sitting on is made up of mussels. Some areas the rock is not visible at all - a carpet of small mussels covers them.

These shells are from a sandy/muddy area in Swan Bay where there is no surf and is inside Port Phillip Bay. Vic.