1 / 10

Mollusks

Mollusks. What is a Mollusk?. A mollusk is a soft-bodied animal that has an internal or external shell. Mollusks include: snails slugs clams squids octopi. Body Plan. Mollusks mostly have a body plan of four important parts:

archer
Download Presentation

Mollusks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mollusks

  2. What is a Mollusk? • A mollusk is a soft-bodied animal that has an internal or external shell. • Mollusks include: • snails • slugs • clams • squids • octopi

  3. Body Plan • Mollusks mostly have a body plan of four important parts: • Foot: The muscular foot takes many forms, including flat structures for crawling, spade-shaped structures or burrowing, and tentacles for capturing prey. • Mantle: The mantle id a thin layer of tissue that covers most of the mollusk’s body. • Shell: The shell is made by glands in the mantle that secrete calcium carbonate. • Visceral Mass: The visceral mass holds all of the internal organs.

  4. Feeding • Mollusks can be: • Herbivores • Carnivores • Filter feeders • Detritivores • Parasites • Snails and slugs feed using a radula. (flexible, tongue-shaped) • Octopi and some sea slugs use their sharp jaws to eat their prey. • Clams, oysters, and scallops filter feeding using their feathery gills.

  5. Respiration • Snails, clams and octopi breathe using gills inside their mantle cavity through diffusion. • Lands snails and slugs respire using mantle cavity that has a large surface are lined with blood vessels. • The lining has to be kept moist so that oxygen can diffuse across its surface. Therefore, land snails and slugs have to live only in moist places.

  6. Circulation • The circulatory system of a mollusk carries its oxygen and nutrients throughout its body. • It is either open or closed: • Open circulatory system: blood is pumped through vessels by a simple heart. It works best for slow-moving mollusks like snails and clams. • Closed circulatory system: can transport blood through an animal’s body much more quickly than an open circulatory system. Faster-moving mollusks such as octopi and squid have a closed circulatory system.

  7. Reproduction • Snails and two-shelled mollusks reproduce sezually by external fertilization by releasing enormous numbers of eggs and sperm into open water. The eggs fertilize and then develop into free-swimming larvae. • In mollusks with tentacles, like octopi and squid, and some snails, fertilization takes place inside. Some may be hermaphrodites (male and female) or they just fertilize eggs from another individual organism.

  8. Groups of Mollusks • Gastropods • Shell-less or single-shelled • Move by use of muscular foot located on ventral side • Includes pond snails, land slugs, sea butterflies, sea hares, limpets, nudibranchs • Bivalves • Two shells held together by one or two powerful muscles • Includes clams, oysters, mussels, and scallops • Cephalopods • Soft-bodied • Head attached to single foot • Is divided into tentacles/arms • Includes octopi, squids, cuttlefishes, nautiluses

  9. Sources • Prentice Hall Biology Book, 2002, Chapter 27, Section 4, pgs. 701-708.

  10. The End

More Related