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Phylum Mollusca Phylum level Characteristics • • • • • soft-bodied with single muscular “foot” internal or external limestone shell complete digestive system coelomates grouped together because of similar developmental patterns • live everywhere: – ocean, freshwater, on land General Body Plan • Foot • Mantle – tissue that hangs or covers some or all of the body • Shell – hard structure can be internal or external • Visceral mass – contains all internal organs • Radula – unique to mollusks – it’s a rasping organ with file like teeth to scrape, crush food • Gills – to extract oxygen from water and can filter food Feeding • Every form of feeding is represented by the various types of mollusks • Some utilize a radula – Herbivores use it to scrape algae off surfaces – Carnivores us it to drill into the shells of prey • Octopi and sea slugs produce poison to subdue prey then use sharp jaws to eat them • Filter feeders use gills to sift food from the water • slug video Respiration • Aquatic species use gills (found within the mantle cavity) to extract dissolved oxygen from the water • Land molluscs breathe via an adapted mantle cavity lined with blood vessels. Must be kept moist for oxygen to enter the cells Circulatory System • Slow moving or sessile species have an open circulatory system – Blood not always within blood vessels – Works through body tissues in open spaces called sinuses • Faster movies species (like octopi) have a closed circulatory system – Blood always within vessels – More efficient Excretory System • Complete digestive system – Solid waste expelled through anus – Metabolic wastes (ammonia) excreted by nephridia (simple kidney like organs) • Nephridia remove wastes and excrete to outside through skin Nervous System • Varies greatly between species – Bi-valves have extremely simple systems consisting of a couple ganglia, nerve chords and sense organs – Octopi and other complex molluscs have developed brains with memory and learning capacity Reproduction • Again, varies between species • Most have separate sexes and fertilization is external (in open water) • More complex species have internal fertilization Ecological & Economic Importance • clams, oysters, scallops all farmed or fished for food • octopus some food value, recreational diving to observe 3 Main Classes • Take some time to read over pages 590 – 592 to learn about the: – Gastropods – Bivalves – Cephalopods • Complete Phylum Mollusca handout Squid External View Squid Internal Anatomy Assignment: 1. Complete Phylum Mollusca handout from last class 2. With your partner, read over the handout for tomorrows dissection 3. Begin to fill in as much of the handout as you can.
