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