Mollusks and Echinoderms

Aquatic: pertaining to or living in water.

Closed circulatory system: a system in which blood is contained within blood vessels at all times.

Echinoderm: an invertebrate that lives on the ocean floor and is characterized by radial symmetry, an internal skeleton, and a water vascular system.

Endoskeleton: an internal supporting skeleton made of bone and/or cartilage.

Mollusk: an invertebrate that has a soft, unsegmented body, a mantle, and a muscular foot.

Open circulatory system: a system in which blood is pumped into the open spaces in the body.

Radula: a specialized feeding structure in mollusks.

Tube feet: the flexible, hollow appendages that help an echinoderm move and collect food.

Water vascular system: a network of fluid-filled vessels in an echinoderm's body that aid in movement, respiration, and food and waste transportation.

Structures of Mollusks:

A mollusk is a bilaterally symmetrical invertebrate that has a soft, unsegmented body, a mantle, a muscular foot, gills, and often a shell. Gills draw oxygen into the blood and remove carbon dioxide from it. An open circulatory system pumps blood into the open spaces in the body.

Types of Mollusks:

  1. Gastropods: The largest group of mollusks, including snails and slugs, living in the ocean, freshwater, shores, and on land. They have a single shell or no shell, use a muscular foot for movement, and utilize a radula for feeding.

  2. Bivalves: Includes oysters, clams, scallops, and mussels. They have two shells, live in a variety of aquatic environments, use a muscular foot for movement, are filter feeders, and produce pearls.

  3. Cephalopods: Includes octopuses, squids, nautiluses, and cuttlefish that live in the ocean. They have a closed circulatory system, capture their prey using tentacles, have a complex nervous system, and swim by jet propulsion.

Echinoderms:

Echinoderms are a type of invertebrate that live in water. They have an endoskeleton, display radial symmetry, and their movement, respiration, and food and waste transportation are facilitated by the water vascular system. Movement and prey capture are made possible by specialized structures called tube feet.

  • Sea Stars: Use their tube feet for movement and to capture prey; they can force their stomach out through their mouth to digest prey.

  • Brittle Stars: Use their tube feet for catching prey and move by slithering their arms like a snake.

  • Sea Urchins: Have movable spines for protection, use tube feet for movement, and have teeth-like structures for feeding.

  • Sea Cucumbers: Use tube feet for movement and sweep food toward their mouth using tentacles.