polyplacophora (chitons)

mantle (pallium)

possessed by all mollusks; encloses most of the visceral organs

foot

ventral muscle that is often highly modified to serve several different functions depending on taxon; may be used for locomotion or clinging

radula

chitinous ribbon with rows of chitinous teeth that is used to rasp off food

ctenidia

morphologically unique gills that are absent in many smalls molluscs and all terrestrial snails and slugs as well as class scaphopoda

coelom in molluscs

reduced to pericardial cavity

polyplacophora

• chitons

• 500 or so species

• slow-moving herbivores or omnivores

• shell divided into 8 separate plates

valves

• eight prominent valves on dorsal side

• head valve by rounded mouth at anterior

• tail valve above anus

• intermediate valves everywhere else

• embedded in heavy tough girdle

valve layers

• tegmentum: exposed outer layer

• articulamentum: smooth, white inner layer

head valve anatomy

rimmed interiorly by a series of insertion teeth

tail valve anatomy

conspicuous sinus at its anterior end and a rounded beak known as a mucro at its posterior end

intermediate valve anatomy

anterior extensions of the articulamentum called sutural laminae, which project under the value anterior to it, and lateral extensions called the insertion plates

jugum/jugal ridge

central spine on tegmentum

esthetes

light-sensory structures on the surface of the shell found along the temental surface edge where it meets the articulamentum

reproductive stuff

• sexes separate (dioceous)

• no sexual dimorphism

sugar glands

empty digestive enzymes into the anterior part of the digestive tract

radula anatomy

• teeth dark brownish to gold

• black caps on teeth are magnetite, an iron salt

Cryptochiton stelleri

• known as gumboot chiton

• largest chiton in the world

• occurs along pacific coast

• seems to have poor attaching capability, but predators avoid it

Placiphorella velata

• veiled chiton

• carnivorous

• traps small crustaceans under large oral hood with finger-like projections