The group Mollusca, established by Cuvier (1798), com­prises of almost 1,00,000 species and is the second largest animal phylum (Fig. -Bilateral symmetry, Triploblastic, segmented coelomate. Octopus has 8 arms and contains no shell. 3. -Respiration by gills, book lungs and trachea. A few molluscs such as Unio possess green glands which mimic the liver in vertebrates. There is a between Mollusca and Echinodermata in terms of morphological, physiological and behavioural characteristics. It protects the soft body . Members of the phylum Mollusca are soft-bodied animals, such as the snail, clam, squid, oyster, and octopus. However, both molluscs and echinoderms are triploblastic, and they possess a complete digestive system. Phylum Mollusca and Phylum Echinodermata belong to the Kingdom Animalia. -Body - Head, Thorax and Abdomen(three parts). They possess osphradia to test the chemical nature of water. GENERAL CHARACTERISTICS BODY CHARACTERS : Soft Unsegmented Triploblastic No jointed appendages SYMMETRY : Bilaterally symmetrical SHELL : Externally mantle secretes a hard , brittle , calcareous shell . It is primitive with segmented body. -Excretion by malpighian tubules. Phylum Mollusca. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. Some secrete a hard shell. They also possess ink glands for protection. 1.100). Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. Start studying Intro to Mollusca Notes and Class Gastropoda notes. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda.The members are known as molluscs or mollusks (/ ˈ m ɒ l ə s k /).Around 85,000 extant species of molluscs are recognized. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. ; Unio contains a digestive gland called Green gland, which is comparable to liver of vertebrates. Phylum Mollusca – -Soft body animals. Phylum Mollusca Characteristics. The bodies are generally very soft and are covered by the hard exoskeleton.They can be found in terrestrial regions as well as in the depths of the seas.You will be amazed to know that the size of the molluscans can range from 20 metres to one millimetre, with a few microscopic animals too. The proportion of undescribed species is very high. Key Points on Mollusca. Many organisms belonging to this phylum have a calciferous shell. Soft-bodied invertebrate covered with protective mantle that may or may not form a hard, calcium carbonate shell; Includes chitons, snails, slugs, clams, oysters, squid, octopus, & nautilus; Second largest animal phylum; Have a muscular foot for movement which is modified into tentacles for squid & octopus Phylum Mollusca 1. -Blood without haemoglobin and circulatory system open. ; Statocysts- for maintaining equilibrium of the body. Generally, these animals live in water. 2 nd largest animal phylum after Arthropoda. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Phylum Mollusca is the second largest phylum. Contains snails, slugs, octopus, squid, and the "shell fish" (clams, oysters,limpets, and scallops); second largest phylum (greater than 100,000 species) B. Each mollusk has a muscular organ called a foot that is used for gripping or creeping over surfaces. Phylum Arthropoda( Jointed Legs) – -Largest phylum. Neopilina is considered as connecting link between Annelida and Mollusca. PHYLUM MOLLUSCA (SOFT BODY) I. CHARACTERISTICS A. The number of fossil species is estimated between 60,000 and 100,000 additional species. The statocysts maintain body equilibrium. Phylum 2. Things to remember.