exer 7

• Mollusca is the second-largest phylum of invertebrate in kingdom animalia.
• Annelida known as segmented worms which divided into three major classes: Polychaeta (clamworms and sandworms), Oligochaeta (earthworms and blackworms) and Hirudinea (leeches).
• Triploblasty is a condition in which an embryo has three primary germ layers: the ectoderm, mesoderm, and endoderm. These germ layers are groups of cells that interact with each other as the embryo grows, forming organs and body tissues.
• The ventral nerve cord is a major structure of the invertebrate central nervous system. It is the functional equivalent of the vertebrate spinal cord.
• haemocoel is especially the body cavity of animals belonging to arthropods and molluscs, which is a reduced form
• coelom is the principal body cavity of annelids, echinoderms and chordates that had originated from the mesothelium
• Class Bivalvia, clams, scallops, and oysters; characterized by a hinged shell of two valves (parts) and a foot used for digging; lack a radula; marine and freshwater filter feeders
• Class Gastropoda, snails, slugs, whelks, limpets, abalones, and nudibranchs; usually possess helical shells and a foot used for crawling; marine, freshwater, and terrestrial herbivores and carnivores.
• Class Cephalopoda, squids, octopods, and nautiloids; usually lack external shells; possess a siphon for jet-propulsion; marine carnivores.
• Class Polyplacophora, the chitons, primarily herbivorous marine species with a shell consisting of many plates (hence its name).
• Class Scaphopoda, the tusk shells or tooth shells, a class of shelled marine mollusk
• Class Aplacophora is a monophyletic group of small, deep-water, exclusively benthic, marine molluscs found in all oceans of the world. All known modern forms are shell-less: only some extinct primitive forms possessed valves.
• Class Monoplacophora, is a polyphyletic superclass of mollusk with a cap-like shell now living at the bottom of the deep sea.
• Class Rostroconchia (extinct) they have a single shell in their larval stage, and the adult typically has a single, pseudo-bivalved shell enclosing the mantle and muscular foot
• Class Helcionelloida is an extinct group of ancient mollusk these are the oldest known conchiferan mollusk that is a mineralized shell.
• Class Polychaeta - mostly marine worms, such as Nereis (the clamworm)
• Class Hirudinea - the leeches (predominantly freshwater), such as Hirudo
• Class Oligochaeta-mostly freshwater and terrestrial worms, such as Lumbricus (earthworms).