Chapter 16 Mollusks

mantle

two folds of skin extending from dorsal body wall that cover/ protect the visceral mass
secretes the shell when present
contains Ctenidia (gills – respiratory system)/ lung
• receives material from various systems:
o Nephridiopores* (exit of excretory syst.)
o Gonopores (exit of reprod. system)
o Anus (exit of digestive system)
aquatic molluscs: osphradia (chemoreceptor)

foot

muscular structure used for…
movement in snails/gastropods
attachment in limpets
burrowing in bivalves (clams)
modified into arms and tentacles for propulsion in cephalopods (squid)

radula

“tongue-like” structure with backward facing “teeth” => Scrape surfaces for food
not in all, only bivalves (clams,oysters etc.) don’t have it

visceral mass

nervous systems, other organs

shell

secreted and lined by the mantle
internal (covered by mantle) or external
3 layers: periostracum: made of conchiolin, outer protection
prismatic: made of CaCO3 crystals
nacreous: very thin CaCO3 crystals_>pearls, inner

nervous system

brain: multiple ganglia, esophageal nerve ring/ collar, longitudinal nerve cords
sensory organs: eyes, tentacles(chem and mechano), osphradia (chem for water quality), statocyst (equilibrium)

Respiratory

‘lungs’ (in fact a highly vascularized MANTLE cavity)
Ctenidia (= gills) (comb-like structure) in the mantle cavity

Circulatory

(open for all BUT cephalopods)
less sufficent to supplying o2, but less costly
blood sinus (hemocoels) where blod drains

Digestive

complete system (mouth and anus, anus on top of head)
extensive ciliary tracts for moving and sorting food particles

EXCRETORY SYSTEM

metanephridia (kidney) open at both ends
nephrostome opens into pericardial cavity →collect fluids, and the nephridiopore opens into the mantle cavity → expel wastes
surrounded by blood vessels that assist in reabsorption

protohephridia vs meta

proto only open 1 way, and use flame cells for filtration, so less complex urine

reproductive system

most dioecious with external fert
but. hermaphrodites + internal exist

life cycle

trocophore larva: hatches out of the egg. In some groups the trochophore metamorphoses into a juvenile
other groups have a more advanced veliger larva develop/emerge after trochophore (trocophore in egg, but veliger larva hatches)

siphuncle

found in cephalopods, living tissue connecting coelomic cavity to all shell compartments – separated by septa. Used for respiration and buoyancy

cephalopod nervous system

most complex
largest brain in invert
complex eyes : cornea, lens, chambers and retina (photoreceptor on retina= rhabdomeres)
balance with statocyst
arms have tactile and chemoreceptor cells

chromatophores

found in not all cephalopods
Elastic cells in the skin for signaling, ‘change color’
granules with pigments, muscles expand form nerve/hormone signal and contract to change color
contract=dark, relax= light

siphon

cephalopod locomotion tool, like a jet propulsion. backwards ONLY in octopus

torsion

process that occurs in gastropod molluscs, such as snails, where the body twists 180° in a counterclockwise direction
allows for more symmetry and balance with uneven shell
Gill, auricle and kidney of right side are lost in most species

loss of right gill provides one solution to foulin problem created by torsion

coiling

process of rotating the body of gastropods to the central axis. In this mantle cavity and anus comes in the same phase
came before torsion
allows for compactness

feeding behaviors of gastropods

herbivore, carnivore, parasite and suspension feeder