Mollusca – Molluscs
The Mollusca, also known as molluscs, are a phylum of animals with many different species and forms. Mollusca comprise over 85,000 species. However, this is more a question of known species, as some estimate that the gastropods include 200000 species itself.
Since the molluscs are a very large phylum, there are many deviations from the “average anatomy”.
In general, the body of the molluscs can be divided into four areas. At the front end they have a head with radula (rasp tongue). On the abdomen is a muscular foot, and on the back is a visceral bag with all internal organs. The fourth region is the mantle, which covers or encloses the visceral sac.
Common to all Mollusca is that a skeleton is missing. Instead, they have an excretion of the mantle cavity, the shell. This is made of calcium carbonate, but is degenerated in many species.
The smallest molluscs are less than 1mm in size. In contrast, the largest cephalopods are up to 18m long.
Habitat and Distribution
There are Mollusca in almost every habitat, except in high mountains. The majority of them live in the sea. However there are also snails which live on land and mussels, which one finds in the fresh water. They are spread from the polar regions to the tropics.
Molluscs make up about 23% of all known marine species and are found in every aquatic environment. They reach a depth of more than 7000m.
Because of the species richness of the molluscs, lifestyle, diet, reproduction, etc. are very different. More specific information is available on the pages of each class and species.
The Bivalvia are a class in the phylum of Mollusca and contain about 8000 species. The majority is marine and feeds on plankton. However, there are freshwater species among the mussels.
The cephalopods are a class of the Mollusca with about 800 species. Around the Canary Islands there are 4 species, which we can observe while diving, two of them very often. They are very intelligent animals. If they lived longer, they would be smarter than man.
The gastropods are a class of molluscs. Estimations vary from 40,000 to 200,000 species. When diving in the Canaries, we often see different species. Especially at night, they crawled out of their hiding places.
The Polyplacophora are a class in the phylum of Mollusca, which contain between 750 and 1000 species. All kinds have eight shell plates, which are surrounded by a girdle. Chaetopleura apiculata is a species of the Polyplacophora, which has the hardest teeth proven in nature.