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Phylum Mollusca

Phylum Mollusca. General Characteristics: soft bodies protected by a shell (most) bodies divided into three parts: visceral mass – contains digestive and excretory organs, and the heart mantle – fleshy layer covering visceral mass, secretes shell

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Phylum Mollusca

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  1. Phylum Mollusca

  2. General Characteristics: • soft bodies protected by a shell (most) • bodies divided into three parts: • visceral mass – contains digestive and excretory organs, and the heart • mantle – fleshy layer covering visceral mass, secretes shell • foot – usually located on the ventral side, may be modified in different mollusks for different functions (usually locomotion)

  3. Nephridium Heart Visceral mass Coelom Intestine Gonads Mantle Stomach Mantle cavity Mouth Shell Radula Anus Gill Radula Mouth Nerve cords Esophagus Foot

  4. all mollusks (except bivalves) have a radula – rasping tongue-like structure located in the mouth, covered with thousands of pointed, backward curving teeth arranged in rows

  5. Four major classes: • Class Polyplacophora – chitons • live on rocky shores in intertidal area • attach to rocks with a muscular foot • shell consists of 8 plates • feeds by rasping algae from rocks using its radula

  6. Class Gastropoda – snails and slugs • large, flat, ventral foot • 1 piece coiled shell (if present) • tentacles with eyes on stalk • feed with a radula • herbivores, scavengers, and carnivores • terrestrial and aquatic

  7. Class Bivalvia – clams, mussels, scallops, and oysters • bivalves – 2 shells connected by ligament acting as a hinge • head, tentacles and radula are absent • foot is modified for burrowing in the mud or sand • filter feeders – gills filter food particles from the water through siphons

  8. Class Cephalopoda – squid, octopuses, and cuttlefish • most highly developed – most intelligent of all invertebrates • internal shell – penn • foot is modified into tentacles (arms) with suckers • large head and eye (similar to vertebrate eye)

  9. Octopus Squid Chambered nautilus

  10. Body systems • Advanced digestive system Intestine Mantle cavity Stomach Anus Mouth

  11. Circulatory system • mollusks have a heart and an open circulatory system • blood is not continuously contained in vessels • blood leaves vessels and washes over tissues in areas called sinuses • blood contains hemocyanin – helps to carry O2 around the body

  12. Excretory system – have a well developed excretory system • body fluids with wastes are drawn into nephridia by cilia • wastes are filtered out and useful materials reabsorbed • Cephalopods have a very advanced nervous system with eyes • Endocrine system – composed of glands that secrete hormones

  13. Coelom Hinge area Mantle Gut Heart Adductor muscle Digestive gland Anus Mouth Excurrent siphon Shell Water flow Palp Foot Incurrent siphon Mantle cavity Gonad Gill

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