Chapter 2 Section 1

Background information about Mollusks They belong to the phylum Mollusca Live nearly everywhere on Earth Most live in water Mountain streams to the deep ocean Some live on land in damp locations. About Mollusks

Background Information about Mollusks Bilateral symmetry All organs are located in 1 area. Open circulatory system for the 1st time. This allows an animal to be bigger About Mollusks

The mantle also produces the mollusk’s shell. What is a mollusk? Invertebrate with a soft, unsegmented body that is protected by a hard outer shell. They have a thin layer of tissue called a mantle over their internal organs. The mantle also produces the mollusk’s shell. Respiratory organ for land mollusks Mollusks

They move with a muscular structure called a foot. Mollusks What is a mollusk? They move with a muscular structure called a foot. Different mollusks have feet adapted for different uses such as crawling, digging, or catching prey

Types of Mollusks Clam Oyster Snails Octopus Scallop

http://videos. howstuffworks http://videos.howstuffworks.com/discovery/29082-the-ultimate-guide-octopus-octopus-ancestry-video.htm Mollusk Videos http://videos.howstuffworks.com/discovery/29071-the-ultimate-guide-octopus-octopus-sense-of-touch-video.htm http://videos.howstuffworks.com/discovery/29070-the-ultimate-guide-octopus-octopus-defenses-video.htm

Organs within a Mollusk Pair of Kidneys: organs that remove waste Gills: Organs that remove oxygen from water Radula: Flexible ribbon of tiny teeth Mollusk ORgans

Covered with tiny, hair like structures called cilia. Mollusk Organs Gills: found in most water-dwelling mollusks They are attached to the mantle Have a rich supply of blood vessels Oxygen from the surrounding water diffuses into the blood and carbon dioxide diffuses out Covered with tiny, hair like structures called cilia. The beating movement of the cilia makes water flow over the gills.

Radula: Flexible ribbon of teeth Unique to this Phylum Act like sandpaper Scrape food from a surface such as a leaf May have as many as 250,000 teeth The arrangement of teeth are used to classify mollusks Mollusk Organs

The broken pieces piled up on the ocean floor After a mollusk died the shell broke into pieces due to waves and currents. The broken pieces piled up on the ocean floor The hard materials underwent a chemical change and became cemented together to form limestone During this process some shells become fossils Early Mollusks What was the 1st evidence of mollusks? Living in the oceans about 540 million years ago The evidence for this comes from fossil shells in limestone rocks

How are mollusks classified? Based on the presence of: Presence of a shell Type of shell Type of foot The arrangement of teeth in the radula Complexity of the nervous system

Gastropods – most numerous Bivalves Cephalopods 3 groups of Mollusks Gastropods – most numerous Bivalves Cephalopods

Gastropod means “stomach foot” Gastropods Gastropod means “stomach foot” Foot is on the same side of their body as their stomach Snails have a single, coiled shell Slugs have no shell Creep along on their broad foot Some are herbivores, some are scavengers, and others are carnivores When a snail is threatened it can pull into its shell also when it is dry out

Ex: Clams, oysters, scallops, and mussels Bivalves Ex: Clams, oysters, scallops, and mussels Have 2 shells that are held together by hinges Do not have a radula Instead food sticks to the mucus that covers the gills Cilia on the gills then removes the food

Found in all kinds of watery environments Bivalves Found in all kinds of watery environments As adults bivalves stay in 1 place or move slowly After their larval stage oysters and mussels attach to a surface underwater Clams are active and burrow into the sand or mud Scallops move from place to place

Octopuses, cuttlefish, nautiluses, and squids are all cephalopods Tentacles can be 5 meters long Capture food with flexible tentacles Suckers on the tentacles receive taste sensations They don’t have to touch something to taste it Large eyes and excellent vision Swim by jet propulsion

Undergo torsion: movement of the anus Class Gastropoda Undergo torsion: movement of the anus Advantage: Balance and protection because the head retreats first into the shell Disadvantage: Anus is near the mouth If torsion didn’t happen the foot would go in before the head Largest and most varied class Aquatic and terrestrial Many marine snails have poison-tipped mouthparts Many serve as an intermediate host for trematode parasites in humans. Mantle used as respiratory organ in land snails

Torsion

2nd largest class of Mollusks Bivalves – 2 shells 2nd largest class of Mollusks Marine & Freshwater 3 shell layers Outer protective layer Middle layers made of calcium carbonate Inner layer Class Bivalvia

Between the mantle and inner layer a pearl is made. The pearl is formed by the mucus fluid covering bacteria or a grain of sand that is irritating the muscle. They have no radula – filter feeders Mussels make pearls – clams do not. Class Bivalvia

Outcompete native mussels Problems: Outcompete native mussels Disrupt spawning of game fish Prolific breeders which damage property Settle on native mussels so that they cannot open Damage pipelines Minnesota has one of the greatest diversities of freshwater mussels in the U.S. Introduced zebra mussel larvae in 1985/1986 to the Great Lakes region from Europe

Most complex of all invertebrates Octopus: shell is absent Squid/ Cuttlefish: Shell is internal Nautilus: Shell is external Class Cephalopoda

Anterior foot is divided into a series of arms Marine Active Predators Class Cephalopoda Anterior foot is divided into a series of arms Marine Active Predators Powerful beak-like jaw and radula Large brain: capable of learning Image-forming eye similar to vertebrates Closed circulatory system Blue-ring octopus have salivary glands with venom