Download Bivalves

Bivalves
Why are they called bivalves?
• The shells of a bivalve are made up of two
halves that are mirror images of each other
and are joined at one edge by a flexible hinge.
• Each half is asymmetrical and rounded, so that
when closed forms a domed space near the
hinged edge of the shell which accommodates
the bulk of the animal's body.
Do Bivalves move?
• Oysters and mussels attach themselves to hard surfaces and remain
in the same spot for their entire life. They adhere to surfaces using
byssal threads secreted by a gland in the foot
• Clams bury themselves in sand or sediment on the seafloor or in
riverbeds. Some just below the surface, others bury deep.
– They may have spines that help to secure them in the sediment and to
prevent predators from dislodging them.
• Boring bivalves have thin, soft shells that are armed with a hard tip.
They bore into solid surfaces such as wood or rock.
• Free-moving bivalves such as scallops use their muscular foot to dig
into sand and soft sediments. They can also move through the
water by opening and closing their valves, an action that pushes
them through the water.
Swimming Scallops
• http://www.bbc.co.uk/nature/life/Pectinidae#
intro
How do bivalves breathe?
• Most bivalves have a pair of large gills which
are located in their mantle cavity.
– enable them to extract oxygen from the water (to
breathe) and to capture food.
– Water is drawn into the mantle cavity and washes
through the gills.
– In species that burrow, a long siphon is extended
to the surface to take in water.
How do bivalves eat?
• Mucus on the gills
helps capture food
and cilia transfer the
food particles to the
mouth.
• Once in the mouth,
food passes into the
stomach to be
digested.
Parts of a bivalve
• Bivalves have a mouth, heart, intestine, gills,
stomach and siphon
• They have an adductor muscle that, when
contracted, holds the two halves of the shell
closed.
• Bivalves have a muscular foot, which in many
species such as clams, is used to anchor their
body to the substrate or dig down into the sand.
• They do not have a head, radula or jaws.
Killer Clams???
• http://www.blueworldtv.com/webisodes/watc
h/killer-clams
Mollusks Quiz on Monday!
• Defining characteristics of each class of
mollusks and exceptions
• Body parts and their function (radula, siphon,
tentacles, operculum, byssal threads, foot)
• Body systems (Reproductive, Circulatory,
Nervous)