Recording-2025-04-01T17:46:45.454Z

Earthworm Regeneration

• Cutting an earthworm can lead to regeneration.
• If cut towards the end, the frontal part can survive and regenerate the posterior end.
• Mollusk Diversity
• Over 100,000 species of mollusks are described, with many more yet to be documented.
• Mollusks generally have soft bodies, some of which secrete shells for protection.
• Found in diverse habitats:
• Aquatic environments (marine and freshwater)
• Moist terrestrial environments

Mollusk Anatomy

• Key anatomical features include:
• Foot
  • Prominent in snails, aids in movement.
• Visceral Mass
  • Contains internal organs, including intestines, covered by the shell.
• Mantle
  • Covers visceral mass; often secretes the shell and facilitates gas exchange.
• Circulatory System
  • Contains a heart that pumps fluid through open vessels (not extensive capillary systems).

Major Groups of Mollusks

• Eight groups, with focus on four:
• Cephalopods (e.g., squids, octopuses)
• Gastropods (e.g., snails)
• Bivalves (e.g., clams, mussels)
• Polyplacophorans (e.g., chitons)
• All mollusks have trochophore larvae.

Gastropods

• Development leads to a 180-degree twist in visceral mass (anus near the head).
• Shell characteristics can vary, with some lineages (e.g., sea slugs, land slugs) losing their shells independently.
• Tentacles with eyes are typical; notable example: a slug with fused eyes.
• Defense Mechanism via Nematocysts
• Some predatory sea slugs (nudibranchs) feed on cnidarians and can utilize their nematocysts for defense.

Reproduction in Gastropods

• Many gastropods are hermaphroditic.
• Unique reproductive behavior: they use structures called love darts in a mating competition (similar to penis fencing).
• Unlike earthworms, which exchange sperm reciprocally, gastropods may vary roles during mating.

Bivalves

• Key trait: hinged shell and strong adductor muscles.
  -