Class Gastropoda

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Class Gastropoda

• Most diverse
• 70,000 living 15,000 fossil species
• Snails, limpets, slugs, conches, periwinkles
• Univalve shell (defense) with operculum
• Intermediate hosts to parasites
• Torsion twists organs in veliger stage
• Some shells coiled

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Feeding

• Many herbivores
• Some scavengers, some carnivores
• Digestion extracellular, in lumen of stomach

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Form and function

• In many, respiration by ctenidia in mantle cavity
• Most have nephridium, circulatory, and nervous
  systems
• Eyes, statocysts, tactile organs, chemoreceptors

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Reproduction

• Monoecious or dioecious
• Exchange sperm or discharge sperm and ova into
  water
• Veliger stage larval or inside egg
• Some ovoviviparous

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3 Subclasses

• Prosobranchs
• Opisthobranchs
• Pulmonates

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Prosobranchs

• Most marine snails some freshwater some
  terrestrial
• Torted gills in front of heart
• Separate sexes
• Operculum

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Opisthobranchs

• Sea slugs, sea hares, sea butterflies, canoe
  shells
• Most marine
• Hide under stones, seaweed
• Detorted
• Anus, gills displaced to right side
• Shell reduced or absent
• Monoecious

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Pulmonates

• All land most freshwater snails and slugs
• Lung present (no ctenidia)
• Monoecious

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Class Bivalvia

• Mussels, clams, scallops, oysters, shipworms
• Most sedentary filter feeders
• No head or radula
• Most marine

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Form and function

• 2 shells with hinge ligament
• Pearls (layers of nacre around irritant)
• Anteroventral foot
• Mantle covers gills
• Incurrent siphon directs water containing food
  across gills and into mouth

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Internal structure

• Heart (2 auricles 1 ventricle)
• 2 kidneys
• 3 pairs of connected ganglia
• Most sense organs poorly developed

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Reproduction

• Separate sexes
• Most external fertilization
• Larval stages trochophore, veliger, spat

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Class Cephalopoda

• Squids, octopuses, nautiluses, devilfish,
  cuttlefish
• Marine predators
• Modified foot expels water
• Nautilus (gas chambers for buoyancy)

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Form and function

• Shell enclosed in mantle (squid, cuttlefish)
• Lost shell (octopus)
• Locomotion--forcefully expel water
• Most--1 pair of gills
• Blood vessel network through gills
• Accessory hearts

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Nervous/Sensory

• Largest invertebrate brain
• Well-developed sense organs
• Complex eyes
• Tactile chemoreceptor cells in arms
• Chemical, visual communication signals
• Rapid color change
• Ink sac

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Reproduction

• Separate sexes
• Modified arm of male inserts sperm into female
• Juveniles hatch from yolky eggs no larval stage

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3 Subclasses

• Nautiloidea
• 2 pairs of gills
• Nautilus
• Ammonoidea
• Extinct
• Coleoidea
• 1 pair of gills
• All cephalopods except Nautilus

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Phylogeny Adaptive Radiation

• Related to annelids and arthropods
• Spiral cleavage
• Trochophore larva
• Hypothetical ancestor
• Small (1mm), worm-like, gliding
• No shell or crawling foot
• Mantle and scales