Mollusk Characteristics

Mollusks, also spelled as molluscs, are living entities characterized by presence of outer, hard shell. This phylum encompasses some of the highly diverse animal species in the world. So, what are mollusks? And what are some major attributes of mollusks? These are invertebrate animals, meaning they lack the vertebral column. More information on mollusk characteristics is given in the next paragraphs.

General Characteristics of Mollusks

As of date, more than 85,000 species of living mollusks are identified scientifically. Contributing to about 23 percent of all marine organisms, it is considered as the largest phylum of the marine world. Underneath the outer shell of mollusks lies a soft body that is prone to desiccation. In short, the shell serves as a protecting structure for these soft bodied animals. Studying mollusk characteristics is interesting for avid zoologists and marine biologists, particularly because of the distinctive features exhibited by the organisms as a means of adaptation to their natural habitat.

Classification
The name mollusks is coined from the Latin word for soft body (Molluscus). The species of mollusks are grouped under the phylum Mollusca and superphylum Lophotrochozoa. The phylum is further classified into 7-9 classes, of which Gastropod is the largest group that comprises snails and slugs.

Habitat
Mollusks are found in highly diverse environment, including high altitude mountains to the deep oceans. They are available in gardens, large trees, thick forests, ponds, streams, estuaries, continental shelves and deserts. Thus, mollusks are nearly ubiquitous in occurrence. You can refer to squids habitat for detailed info on the same.

Locomotion
Some truly aquatic mollusks are fast swimmers, while others are stationary animals that remain attached to ground rocks or plant parts. You will also find many of them inhabiting underground habitats by their burrowing habit. In addition, some species of mollusks move from one place to another by crawling.

Size
The size of mollusks may range from small, inconspicuous body (about 0.1 inch) to as large as 70 m in case of some squids. The giant squid, recorded as the largest invertebrate animal species, has a body length of approximately 12 m and tentacles measuring about 50 m. Likewise, the weight of microscopic mollusks is measured in mg, while an adult giant squid weighs about 270 kg.

Examples
The nudibranchs are a group of mollusks, remarkable for their vibrant colors. These colorful marine animals lost outer shell during the process of evolution. Some of the commonly known examples of mollusks are snails, slugs, oysters, mussels, squids, octopus, etc.

Common Characteristics
Despite the appearance and size diversities of mollusks, there are some basic features of mollusks shared by all species. They are soft limbless body (bilaterally symmetrical), absence of skeletons and cold bloodedness. The body can be separated into three basic parts, head, mantle and muscular foot. It is the mantle that secretes shell. Some species possess internal skeletons, examples of which are cuttlefish and octopus.

Speaking more about animal facts on mollusks, the anatomy shows a gut with mouth, basic digestive parts and anus at the end. They possess all major organ systems like brain, open heart, kidneys and gills, but lack cavities. The food habit of mollusks varies in accordance to species. Reproduction takes place by means of sexual methods.

This was a brief overview of mollusk characteristics. Some species have strikingly beautiful shells, which are collected for decorative purposes. Also, pearls are some of the most valuable jewels harvested from oysters. Marine biologists are sure of the occurrence of many other mollusks species in various habitats, especially in the vast seas and oceans. So, it is quite likely that the number of mollusks will increase with the passage of time.