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