Questions and Answers
What is the phylum of organisms characterized by having a soft body, muscular foot, and (most often) a protective shell?
What are the two main types of classes within Phylum Mollusca?
Polyplacophora and Cephalopoda
Mollusca is characterized by having __________ symmetry.
bilateral
What is the main feeding method of bivalves?
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What class of mollusks are known for their eight shell plates?
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Cephalopods have a closed circulatory system.
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Which class of mollusks is commonly called tusk shells?
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How do gastropods primarily feed?
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What type of reproduction is most common in bivalves?
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What habitat do scaphopods typically inhabit?
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Study Notes
Phylum Mollusca
- Characterized by soft bodies, muscular foot, and typically a protective shell.
- Bilateral symmetry, more than two cell layers, tissues, and organs.
- Lacks body cavity, possesses a complete digestive system with mouth and anus.
- Monomeric body form, can have dorsal or lateral shells made of protein and calcareous spicules.
- Nervous system includes a circum-oesophageal ring, ganglia, and paired nerve chords.
- Open circulatory system with a heart and an aorta.
- Gaseous exchange occurs through ctenidial gills.
- Possesses a pair of kidneys and predominantly reproduces sexually in a gonochoristic manner.
- Diverse diet, inhabiting varied environments.
Class Polyplacophora
- Chitons exemplify this class, with flattened bodies covered by eight shell plates.
- Large, flat foot enables attachment to rocks tightly.
- Feeds on algae and organisms using radula for scraping.
- Reproduction is sexual and internal, commonly found in intertidal zones.
Class Scaphopoda
- Known as tusk shells, scaphopods have tube-like shells open at both ends.
- Burrow into sediments and capture prey with foot or specialized tentacles.
- Primarily feed on foraminiferans.
- Features separate sexes with external reproduction, found in intertidal zones and depths of several thousand meters.
Class Gastropoda
- Most members possess univalve shells with an aperture and often have an operculum.
- Occupy diverse habitats from shorelines to ocean depths and pelagic zones.
- Various feeding behaviors: herbivores, carnivores, scavengers, deposit feeders, and filter feeders.
- Typically exhibit internal fertilization and a larval stage known as trochophore.
Class Cephalopoda
- Comprises free-swimming carnivorous members with complex structures including shell valves, siphon, and tentacles from the head.
- Utilize muscle cells to tear apart and swallow food, primarily feeding on fish and crustaceans.
- Separate sexes with external reproduction.
Class Bivalvia
- Characterized by shells divided into two jointed halves called valves (e.g., clams, oysters, scallops).
- Lack of head, no radula; bodies are laterally compressed, shells hinged dorsally.
- Most are filter feeders, eating plankton by filtering particles from water through gills.
- Typically exhibit separate sexes; fertilization usually occurs in the water column, with many species burrowing into sand or mud.
Chitons
- Feed on algae and organisms scraped from rock surfaces using their radula.
- 75% of their gut contents may include sediments; some variants feed on small crustaceans and invertebrates.
- Flattened bodies covered by eight shell plates held together by a tough girdle.
- Can roll into a ball for protection and have a large flat foot for attachment.
Scaphopods
- Commonly known as tusk shells, characterized by an open-ended tube-like shell.
- Utilize a protruding foot for burrowing, while water enters and exits through the smaller end for respiration and food capture.
Gastropods
- Herbivorous species graze on algae, while carnivorous types follow prey scents using a proboscis, employing sulfuric acid and specialized radulae for predation.
- Scavengers and deposit feeders consume organic remnants mixed with minerals, while filter feeders use ciliary action to trap food particles.
Bivalves
- Filter feeders that process water through inhalant openings, with gills filtering food particles.
- Food is moved to the mouth by palps before entering the digestive system.
Cephalopods
- An advanced class of carnivores utilizing beak-like jaws and radula to consume prey, including fish, crustaceans, and squid.
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Description
This quiz focuses on the key characteristics of the Phylum Mollusca. Explore the details of these fascinating organisms, including their body structure, symmetry, and unique features. Perfect for students studying biology or marine life.
