Mollusks and Echinoderms Section 1 – Mollusks (Gastropods, Bivalves, and Cephalopods) Mrs. Donna Gentile – September, 2014

Characteristics of Mollusks Examples: clams, oysters, scallops, snails, squids Invertebrates with soft, unsegmented bodies that are often protected by a hard outer shell.

Characteristics of Mollusks – cont. Thin layer of tissue called a mantle that covers its internal organs Biologists classify mollusks into groups based on their physical characteristics: shell, type of shell, type of foot, type of nervous system

Body Structure Bilateral symmetry Digestive system with 2 openings Body parts are not repeated – internal organs are located together in one area

Circulatory System Most have an open Circulatory System – blood is not always inside blood vessels Blood sloshes over the organs and returns to the heart

Obtaining Oxygen Most mollusks that live in water have gills Gills have cilia and a rich supply of blood vessels Carbon dioxide, a waste gas, moves out of the blood and into the water

Snails and Slugs Gastropods are the largest group of mollusks Live in oceans, rocky shores, fresh water, on land Have a single external shell or no shell at all

Obtaining Food Some are herbivores, scavengers, carnivores Use a radula to obtain food Herbivores – sandpaper to tear through plant tissue Carnivores – drill a hole, scrapes

Movement Creeps along on a broad foot Foot oozes a carpet of slippery mucus which helps make it easier for the gastropod to move

Two-Shelled Mollusks Bivalves – are mollusks that have 2 shells held together by hinges and strong muscles Examples: oysters, clams, scallops, mussels Found in all kinds of watery environments

Obtaining Food Filter feeders that strain tiny organisms from water Capture food as water flows over their gills, food sticks to the mucus that covers the gills, cilia move the food particles into it’s mouth Most bivalves are omnivores

Movement Don’t move quickly Larvae – float or swim Adults – stay in 1 place or use their foot Oysters and mussels attach themselves to rocks Clams move

Protection Sand gets stuck between a bivalve’s mantle and shell – it irritates the soft mantle – mantle produces a smooth, pearly coat to cover the object Sometimes a pearl forms

Octopuses and Their Relatives Cephalopods are ocean-dwelling mollusks whose foot is adapted to form tentacles around its mouth. Examples are:octopuses, squid, nautiluses, cuttlefishes

Obtaining Food Carnivores - uses tentacles to capture the food and crush it Tentacles have suckers that receive sensations of taste and touch It doesn’t have to touch something to taste it because the suckers respond to chemical in the water – tastes before touching it

Nervous System Large eyes – excellent vision Most complex nervous system of any invertebrate Large brains – can remember and learn

Movement Swim by jet propulsion Squeeze a current of water out of the mantle cavity and through a tube Turning the tube changes the direction they’re going

Echinoderms Section II

Characteristics of Echinoderms Examples: Starfish, sea cucumber, sea urchins Marine dwelling Invertebrates Spiny skin Able to REGENERATE – regrow missing parts

Body Structure Endoskeletons Penta-radial symmetry

Circulatory System Network of fluid-filled canals that function in gas exchange, feeding and in movement. Contains a central ring and areas which contain the tube feet The tube feet poke through holes in the skeleton and can be extended or contracted. They do not have a true heart and the blood often lacks any respiratory pigment (like hemoglobin).

Obtaining Oxygen Echinoderms have a a poorly developed respiratory system. They use simple gills and their tube feet to take in oxygen and pass out carbon dioxide.

Obtaining Food Majority are carnivores – feed on sponges & mollusks Stomach is flipped out of mouth and surrounds soft body parts of prey. Digestive juices are secreted and liquefy prey. Mouth, stomach, digestive gland & anus

Movement When echinoderms move in a manner such as walking or crawling, they pump sea water through a series of internal body canals. The water is used to inflate some of the tube feet, causing them to expand. In many species, the tube feet are equipped with suckers that grip onto the sea floor. The feet hold tight to the bottom as muscles within the feet contract, enabling the animal to propel itself.”

Nervous System Echinoderms do not have brains, they have nerves running from the mouth into each arm or along the body. They have tiny eyespots at the end of each arm which only detect light or dark. Some of their tube feet, are also sensitive to chemicals and this allows them to find the source of smells, such as food.