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This text provides an overview of the Phylum Mollusca, including their soft bodies, foot, mantle, and shells. It describes the three classes of mollusks - Gastropods, Bivalvia, and Cephalopoda - highlighting their distinct characteristics. The text also discusses mollusk feeding, respiration, circulation, excretion, nervous systems, reproduction, and the specific examples within each class. Overall, it offers a comprehensive understanding of the Phylum Mollusca.
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Phylum Molluska • 1. Soft bodies • 2. Foot • 3. Mantle • 4. Most have shells
Molluska Classes • Gastropods – mollusk with ONE shell • Bivalvia- mollusk with TWO shells • Cephalopoda – mollusk with and internal shell or no shell at all. Exception chambered nautilus
I. Characteristics • A. Coelomates – True coelom, a hollow fluid filled cavity surrounded by a mesoderm, body wall of muscles That are separated from the gut and can aid in blood transport. • B. Trochophore – Larvae stage of mollusks and annelids.
Mollusca – body plan A. All have similar body plans – foot, soft body, mantle and shell B. Foot is a soft muscular structure, used for movement. C. Radula- Flexible tongue like structure present in snails and slugs, used to scrap food off of leaves. D. Visceral Mass – Body area that contains all the mollusks organs
C. Mantle is a thin delicate layer of tissue that surrounds the body, and secretes a calcium carbonate shell. E. Shell - also called valves and is secreted by the mantle. 1. 3 Layers a. Inner – smooth, protects soft body. b. middle- calcium carbonate, strength c. Outer – protects shell against sea environment.
2. Feeding A. Much variation, carnivores, herbivores, filter feeders, detritus feeders, scavengers or parasites 3. Respiration A. Aquatic mollusks exchange gases through gills and through exposed wet skin. B. Terrestrial mollusks usually exchange gas through a specialized adapted mantle cavity.
4. Circulation A. Open circulatory system for clams and oysters. Fluid called hemolymph that moves through channels and pools into tissues spaces called hemocoel where organs are bathed B. Closed circulatory system for fast moving animals, vessel driven.
5. Excretion A. Solid waste passes out through the end of the gut, anus. B. Nitrogen waste are removed from the blood by organs called nephridia. 6. Nervous systems A. Clams and relatives have few ganglia (cluster of nerves )and nerve cords. B. Octopus and relatives have well-developed brains, excellent vision, touch and taste 7. Reproduction A. Some mollusks are hermaphrodites, some external, some internal.
8. Classes: A. Gastropods 1. Examples – snails, slugs, abalone, sea hares nudibranchs 2. One shell is used for protection or no shell. 3. Torsion –process where the visceral mass twists bringing organs to the front of the animals body. 4. Non shelled animals use poison or are bad tasting
B. Bivalves 1. Examples – clams, oysters, mussels, and scallops 2. 2 shells present for protection 3. Shells are hinged together with strong muscles called adductor muscles. 4. Some produce nacre (mother of pearl)
5. Siphons – filter feeders use fleshy tubes that extend outside and between the shells. • A. Incurrent siphon – Pulls water in filled with nutrients. • B. Excurrent Siphon – Release waste.
6. Feeding in Bivalves • A. Gills – water enters through incurrent siphon, food gets caught on sticky mucus on gills. Food is than moved to the mouth to indest. ( MUCUS FEEDERS)
C. Cephalopods = “head” “footed” animals 1. Examples – chambered nautilus, octopus, squid, and cuttlefish. 2. Largest, most active and most intelligent 3. 8 tentacles and 2 arms = 10 appendages (squid, cuttlefish) - 8 arms (octopus) 4. Suckers found on tentacles. 5. Internal shells or no shell, exception, (Nautilus) 6. Ability to change color, Chromatophore pigment. 7. Some squirt ink, defense. 8. Beak – powerful jaws for eating.
