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Biology 20: Diversity of Life Invertebrates – Teacher Notes Invertebrates Phylum Mollusca (Snails, Bivalves, Octopus, Squid) The word “Mollusca” means soft Bilateral symmetry Soft body with internal or external shell Have a muscular foot for movement - can be modified into arms or tentacles Breathe through gills or lungs located below a protective layer called the mantle The mantle forms the shell in some species and also protects the body organs Visceral mass protects the internal organs All mollusks except bivalves contain a rasping, tongue-like radula for scraping food. The circulatory system consists of a three-chambered heart and openflowing system except for octopus & squids which have a closed circulatory system. Reproduction is sexual even in hermaphroditic forms. Mollusks go through a free swimming larval stage called the trochophore. Classified according to their foot and shell. Three major classes of mollusks: 1. Gastropods (snails, slugs) shell-less or single shelled move by a muscular foot attached to their belly snails without shells are called slugs Biology 20: Diversity of Life Invertebrates – Teacher Notes 2. Bivalves (clams, oysters) have two shells hinged together by a ligament muscles open and close the shells siphons circulate water containing food and oxygen through the bivalve gills extract the oxygen from the water move by jet propulsion muscular foot can be extended from the shell for movement or anchoring. 3. Cephalopods (octopi, squid) soft-bodied , head is attached to foot foot is divided into tentacles with sucking disks most have beaks, tentacles and jaws and are active predators small internal shells or no shell at all the most intelligent of all invertebrates use siphons to move by jet propulsion. Representative Mollusks: a) Snails o Gastropod meaning it walks on its belly o Most snails are marine and have gills to breathe o Land snails have an air hole for breathing o Snails can be very large. The helmet snail can be as big as 15 pounds! b) Squid o Marine animals o Blast clouds of ink when threatened o Translucent body, can be iridescent, and can change colors o Are the fastest swimmers among the invertebrates – some “flying squid” have been known to leap out of the water at speeds of 20 mph o The giant squid is the largest cephalopod. It can be up to 60 meters in length and has been known to eat whales. Biology 20: Diversity of Life Invertebrates – Teacher Notes Phylum Arthropoda (Insects, Spiders, Crustaceans) The word “Arthropoda” means jointed Hard exoskeleton which is usually composed of substance called chitin Go through periodic ecdysis (molting) as they shed or molt their exoskeleton Have specialized body segments (head, thorax, cephalothorax, & abdomen) Have jointed appendages such as legs, antenna, and mouthparts Have an open circulatory system (blood is pumped out of blood vessels into the body) Further classified according to their type of appendages Major Group Characteristics Centipedes Have flat bodies with segments. Each body segment has one pair of legs. Has 1 pair of antennae. Millipedes Have round bodies with many segments. Each body segment, except the first four, has two pairs of legs. Has 1 pair of antennae. Crustaceans Have two main body parts, two pairs of antennae, large claws, and four pairs of legs. Most live in water. Have gills for gas exchange. Arachnids Have two body sections and four pairs of legs. Have book lungs for gas exchange. Insects Have three body sections and three pairs of legs. Some have wings. Examples Centipedes Millipedes Lobsters, shrimp, crabs, and crayfish Spiders, scorpions, ticks Ants, lady bugs Biology 20: Diversity of Life Invertebrates – Teacher Notes Arthropods make up the largest phylum in the animal kingdom. Why have they been so successful? a) First true walkers b) Have adapted for all environments – land, water, and air c) Exoskeleton provides protection d) Exhibit social behavior (e.g. colonies of ants and their related hierarchy, communication between bees) Arthropods have both a helpful and harmful relationship with humans. Helpful Pollinate plants Act as decomposers Eat things harmful to humans Produce materials (e.g. honey, silk) Harmful Damage crops Vectors of diseases Compete with humans for food and shelter Phylum Echinodermata (Starfish, sand dollars, and sea cucumbers) The word "echinoderm" means spiny skin Radial symmetry with five arms that extend from a middle body section Have an endoskeleton made up of spines Adults have no head or brain and move by extendable tube feet. Have a water vascular system made up of a system of canals that help the organism feed and move. This hydraulic water system is strong enough to help starfish open clam shells. Biology 20: Diversity of Life Invertebrates – Teacher Notes Skin gills are used for respiration and waste removal. Can reproduce asexually by regeneration whenever parts are dropped or by fragmentation Can reproduce sexually with external fertilization Representative Echinoderm: a) Starfish o Have 5 arms set off from a central disk and their mouth located on the underside or oral surface o Are active marine predators o Consume clams by turning their stomach inside out and sticking it into the clam shell to digest the clam