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Chapter 27 Mollusk & Segmented Worms Mollusk: Phylum Mollusca Consist of slugs, snails & animals that once lived in shells on the beach Range from slowmoving slugs to jet propelled octopus Mollusk Characteristics Most live in the ocean, on land & freshwater Some have shells All are bilateral symmetry with coelom & 2 body openings Have a muscular foot for movement Have a mantle A mantle is a thin membrane that surrounds the internal organs. In shelled mollusk, the mantle secretes the shell Mollusk live in a wide variety of habitats Ocean: oysters, mussels live attached to the ocean floor Mollusk live in a wide variety of habitats Ocean: octopus swim freely Mollusk live in a wide variety of habitats Land Dwelling: slugs & snails can be found in moist tropical & temperate climates Classes of Mollusk 1. 2. 3. There are 7 classes of mollusk. The 3 that include the most common are Gastropoda Bivalvia Cephalopoda They look different on the outside, but they are similar on the inside Bodies are composed of a foot, mantle, shell & visceral mass that contains organs Gastropod-One shelled mollusk “Stomach Footed Mollusk” Land snails, slugs & marine limpet (sea slug) Name comes from the way the foot is positioned under the rest of its body Many are hermaphrodites Marine Limpet Sea Slug Land Snail Land Slug Body Structure Radula-a tongue-like organ with rows of teeth used to scrape, grate or cut food Simple nervous system w/ small brain Blood is pumped by the heart Open circulatory system Radula Cross-Section of a Snail Mantle Shell Gut Head Visceral mass Shell Mantle Foot Foot Shelled Gastropods Snails, abalones, & conchs May be plant eaters, predators or parasites Abalones Conchs Gastropods without Shells Sea Slugs, & Slugs Sea Slugs feed on jellyfish & use its nematocysts to repel predators Some secret strong unpleasant smelling mucus They are bright in color Bivalves-2 Shelled Mollusk “Muscle Footed Mollusk” Oysters, Clams & Sea Scallops that have a 2 hinged shell They strain their food from the water Do not have a distinctive head or radula Strong hinge allows the shell to open and close Bivalves use cilia to beat & draw in water over the gills pushing food particles to the stomach Cephalopods-Head footed mollusk Predatory squid, octopus & the chambered nautilus Have sharp eyesight, muscular tentacles, jet propulsion, complex brain & ability to learn Closed circulatory system Octopus & Squid Often apply their intelligence to capturing prey or avoiding harmful situations Instead of muscular foot, have tentacles w/ suckers for moving & capturing food Octopus in a coconut shell Octopus The Octopus Octopus have separate sexes Make adapted to transfer sperm into the females body Fertilization is internal, eggs laid outside the body Use “ink” it confuse predators Squid Squids are known as "the ice cream cone of the sea" because they are a favorite food of many ocean dwellers Backbone & ink sack used to write with Cross-Section of a Squid Arm Head Tentacle Visceral mass Mantle Mantle Shell Foot Gut Chambered Nautilus Only shelled member of the cephalopod family Segmented Worms: Phylum Annelida Segmented Worms Include Bristle worms, Earthworms, and Leeches Term annelid means “tiny rings” Bilateral & coleom with 2 body openings Characteristic of Annelids All Annelids Are made of segments Bodies appear to be divided into rings Segmentations continue internally Each ring is its own muscle-helps shorten & lengthens Parts of the Earthworm Setae Intestine Gizzard Brain Nerve Crop Aortic arches Parts of the Earthworm Mouth: takes in soil, beginning of the digestive tract Crop: holds soil before it is passed to the gizzard Gizzard: grinds food into small pieces so it can be absorbed. Setae: helps earthworm move by providing a way to anchor their bodies in the soil Circulatory system: closed Nervous system: nerve fibers connected by ventral nerve cord to a simple brain Nephridia: excretory structure Where do they live? Everywhere except in frozen soils of polar regions & dry sand like soils of the desert Bristleworms: Mostly marine organisms Have distinctive head with eyes & tentacles Each body segment has a pair of appendages called parapodia which are bristle like structures Earthworms Are nocturnal animal Come to surface but stay close to their burrows Cool moist soil provides protection during the day Water in the soil is a source of oxygen that soaks into the body through the skin Earthworms are hermaphrodites 2 worms exchange sperm Each worm forms a capsule for the egg & sperm The eggs are fertilized in each worms capsule & slipped off into the soil 2-3 weeks young emerge Leeches Segmented worms with flatten bodies & no bristles Found in different habitats mostly fresh water Have front & rear suckers Parasites that suck blood OUCH!!! The bite is not painful b/c the saliva contains a chemical that acts as an anesthetic Keeps blood from clotting & increase blood flow Can ingest 2-5 times its own weight in one meal Once fed-it may not eat again for a year WOW!