Exam policies

• Alternate seats (as possible)
• Regrades only offered for exams written in pen
• Out of fairness, please …
• Start only when told
• Do not leave during last ten minutes (after 10:35)
• Stop immediately when told exam is over
• Stay in seat until all exams are collected

Class Gastropoda

• Synapomorphies
• Torsion
• Greater concentration of visceral mass dorsally

Torsion

• Advantages
• Osphradium now anterior
• Mantle cavity gets clear water
• Head withdrawal
• Problem
• Feces dumped on head!
• Different solutions in different groups of gastropods

Class Gastropoda - Three subclasses

• Three major groups

Subclass "Prosobranchia"

• Paraphyletic
• Marine snails, mostly with shells (some have lost them secondarily)
• Three grades
• Archaeogastropoda
• Mesogastropoda
• Neogastropoda

Grade Archaeogastropoda

• Most primitive
• Paired bipectinate ctenidia
• Paired osphradia
• Medial anus
• Problems
• Feces must vent over head
• Turbulence -> fouling in mantle cavity

Grade Archaeogastropoda

• Most primitive
• Problems
• Feces must vent over head
• Turbulence -> fouling in mantle cavity
• Solutions
• Dorsal perforations

Grade Mesogastropoda

• Loss of right
• Ctenidium
• Osphradium
• Less crowding, better flow!
• Longer rectum
• Feces dumped on right side
• Still have sediment fouling
• Tubulence at bipectinate gill

Grade/Clade Neogastropoda

• Unipectinate gills
• Less turbulence, fouling
• Increased separation of inflow/outflow
• More elongate mantle cavity -> feces farther
• Mantle forms siphon

Subclass Opisthobranchia

• Sea slugs and relatives
• 2° Bilateral symmetry
• Torsion, then detorsion
• Anus moved to rear
• Reduction, loss of shell

Subclass Opisthobranchia

• Sea slugs and relatives
• ...
• Reduction or loss of shell
  • Evolve new defenses, e.g.
  • Swimming
  • Noxious chemicals
  • Kleptocnidism (i. e., they got somebody else's stingers!)

Subclass Opisthobranchia

• Sea slugs and relatives
• ...
• Reduction or loss of shell
• Reduction or loss of mantle cavity and gills
• Respiratory evaginations of epidermis

Subclass Pulmonata

• Land snails, slugs, and freshwater snails
• Ctenidium lost
• Mantle forms a lung (vascularized mantle)
• Pneumostome -- it's just an opening