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