It protects the soft body . Learn vocabulary, terms, and more with flashcards, games, and other study tools. Phylum Mollusca 1. Some secrete a hard shell. A few molluscs such as Unio possess green glands which mimic the liver in vertebrates. Phylum Mollusca Characteristics. 3. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. GENERAL CHARACTERISTICS BODY CHARACTERS : Soft Unsegmented Triploblastic No jointed appendages SYMMETRY : Bilaterally symmetrical SHELL : Externally mantle secretes a hard , brittle , calcareous shell . Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. Phylum 2. -Blood without haemoglobin and circulatory system open. 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. Phylum Mollusca – -Soft body animals. The number of fossil species is estimated between 60,000 and 100,000 additional species. Start studying Intro to Mollusca Notes and Class Gastropoda notes. Things to remember. 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. -Respiration by gills, book lungs and trachea. -Excretion by malpighian tubules. They also possess ink glands for protection. There is a between Mollusca and Echinodermata in terms of morphological, physiological and behavioural characteristics. However, both molluscs and echinoderms are triploblastic, and they possess a complete digestive system. ; Statocysts- for maintaining equilibrium of the body. They possess osphradia to test the chemical nature of water. 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 ; Unio contains a digestive gland called Green gland, which is comparable to liver of vertebrates. Phylum Arthropoda( Jointed Legs) – -Largest phylum. Neopilina is considered as connecting link between Annelida and Mollusca. -Bilateral symmetry, Triploblastic, segmented coelomate. Phylum Mollusca and Phylum Echinodermata belong to the Kingdom Animalia. Generally, these animals live in water. The statocysts maintain body equilibrium. The proportion of undescribed species is very high. Members of the phylum Mollusca are soft-bodied animals, such as the snail, clam, squid, oyster, and octopus. -Body - Head, Thorax and Abdomen(three parts). It is primitive with segmented body. 2 nd largest animal phylum after Arthropoda. Each mollusk has a muscular organ called a foot that is used for gripping or creeping over surfaces. Octopus has 8 arms and contains no shell. Key Points on Mollusca. Many organisms belonging to this phylum have a calciferous shell. PHYLUM MOLLUSCA (SOFT BODY) I. CHARACTERISTICS A. Contains snails, slugs, octopus, squid, and the "shell fish" (clams, oysters,limpets, and scallops); second largest phylum (greater than 100,000 species) B. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. 1.100). The group Mollusca, established by Cuvier (1798), com­prises of almost 1,00,000 species and is the second largest animal phylum (Fig. Phylum Mollusca. Phylum Mollusca is the second largest phylum.