Mollusca

Limpet

an uncoiled, caplike, low-profile shell and a large creeping foot; appears often in molluscan evolution

Radula

rasplike organ used to graze on the biofilm of microscopic algae and other small sessile organisms; flexible longitudinal ribbon of transverse rows of tiny chitinous teeth

Mantle

Formed by the body wall falling over the visceral mass

Gills

in molluscs, known as ctenidia; several pairs, one of which is located in the posterior mantle cavity

Central axis

generalized gill attached to the mantle along one edge

Gill filaments

leaflike tissues that arise from opposite sides of the axis in two rows

Bipectinate

describes the primitive molluscan gill with two rows of filaments

Monopectinate

describes gills with filaments on only one side of the axis, which many living molluscans have

Interfilamentary water spaces

one of the sections the gills divide the mantle into; ventral and infrabranchial

Inhalant chamber

one of the sections the gills divide the mantle cavity into; ventral and infrabranchial

Exhalant chamber

one of the sections the gills divide the mantle cavity into; dorsal and suprabranchial

Lamellae

Exposed gill surfaces formed by combined edges of the filaments

Lateral cilia

generate the respiratory current through the mantle cavity to facilitate gas exchange

Frontal cilia

generate a current moving away from the gill axis toward the tip of the filament to prevent particles from clogging the interfilamentary spaces

Pseudofeces

particles trapped in mucus off of the frontal lamella that are released into the exhalant water current

Abfrontal cilia

participates in transporting pseudofeces

Hypobranchial glands

two patches of mucus-secreting epithelium located on the mantle roof that lie downstream of the gills and trap sediment in the exhalant current

Afferent branchial vessel

Brings unoxygenated blood to the gill filaments

Efferent branchial vessel

removes oxygenated blood from the gill and transports it to the heart

Osphradia

pair of sensory organs in the inhalant water current; its receptor cells monitor the water entering the mantle cavity for chemicals and perhaps sediment

Pedal hemocoel

blood sinus contained in the foot

Pedal retractor muscles

extend from the inner surface of the shell to the foot; contraction of these pulls the shell toward the foot or vice versa

Microphagous browser

describes the diet of the generalized mollusc, which uses its radula to scrape microscopic algae, other organisms, and other detritus from hard substrata

Odontophore

the connective tissue that supports the radula within the mouth

Radular sac

a ventral evagination of the floor of the buccal cavity that secretes and contains the radula

Gonocoel

part of the coelom which contains the gonad

Cerebral ganglia

also called the brain; receives sensory nerves from the eyes, tentacles, and statocysts

Cephalic tentacles

Chemomechanoreceptive organs on the head

Veliger

final larval form that has a foot, shell, and two laterally ciliated lobes

Planktotrophic

larval form that feeds on tiny suspended particles and typically have long planktonic lives

Lecithotrophic

larval form that depends on yolk and usually has a short planktonic life

Direct development

molluscs such as cephalopods and many gastropods that don't have a larval stage

Torsion

only characteristic common to all gastropods; a 180º counterclockwise rotation of the visceral mass, shell, mantle, and mantle cavity with respect to the head and foot

Whorls

several complete coils that make up the shell and form a spiral around a central node

Detorsion

movement of the mantle cavity and/or its contents to the right side of the body that is accomplished by the reversal of one phase of torsion

Operculum

a doorlike, horny disc attached to the foot that closes the aperture when the foot and head are retracted to protect the snail from predation and desiccation

aposematically colored

A bright warning color

gastropoda

• Class of mollusks including slugs, snails, periwinkles, and limpets.

• Characteristics: Torsion of visceral mass, coiled shell, ctenidium for breathing.

Polyplacophora

• Class of mollusks known as chitons.

• Characteristics: Eight overlapping valves, found worldwide in marine environments.

Torsion in Gastropods

• 180º counterclockwise twisting of the visceral mass.

• Benefits: Escaping predators in veliger stage, greater elongation.

• Downsides: Anus located above mouth, potential fouling.

Reproduction in Mollusks

Mostly dioecious, some hermaphroditism.

Importance of Mollusks

• Vital for human consumption, pearl production, natural filtration.

• Threats: Overfishing, invasive species, habitat loss.