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The shell is typically bilaterally symmetrical, with the hinge lying in the sagittal plane. Adult shell sizes of bivalves vary from fractions of a millimetre to over a metre in length, but the majority of species do not exceed 10 cm (4 in).
- What is the body structure of bivalves?
- What structure produces the shells of bivalves?
- What is the natural position of a bivalve at rest?
- Where are bivalve shells found?
- Do bivalves have eyes?
- Are bivalves sessile or motile?
- Which two structures are missing in bivalves but are present in all other mollusks?
- Do bivalves have tentacles?
- Do bivalves feel pain?
- Are bivalves Monoecious or dioecious?
- Do bivalves have gills?
- Is an octopus a bivalve?
- Do bivalves have a mantle?
- How do bivalves burrow?
- What type of fossil is a bivalve?
What is the body structure of bivalves?
Bivalve molluscs are completely enclosed by a shell made of two valves hinged at the top. A hinge ligament made of elastic protein joins the two halves of the shell together, and large adductor muscles between the two valves hold them closed.
What structure produces the shells of bivalves?
The bivalve shell is made of calcium carbonate embedded in an organic matrix secreted by the mantle. The periostracum, the outermost organic layer, is secreted by the inner surface of the outer mantle fold at the mantle margin.
What is the natural position of a bivalve at rest?
Bivalves live with their shells open at rest and must exert energy to close it and keep it closed. This is why so many brachiopods are found complete and clams are found as only one shell present. When they die, brachiopods stay together in their natural, at-rest and sealed position.
Where are bivalve shells found?
Bivalves are very common in essentially all aquatic locales, including saltwater, brackish water, and freshwater. The shells of bivalves commonly wash up on beaches (often as separate valves) and along the edges of lakes, rivers, and streams.
Do bivalves have eyes?
Many bivalves possess eyes along the ventral margin of their mantle, which lines the shell. These are called pallial eyes, in reference to a mantle or cloak (Gk.
Are bivalves sessile or motile?
Bivalves proper emerged more than 500 million years ago, during the Cambrian period. They are generally sessile, meaning individuals are permanently or semi-permanently attached to a substrate (Georgia Southwestern State University).
Which two structures are missing in bivalves but are present in all other mollusks?
In keeping with a largely sedentary and deposit-feeding or suspension-feeding lifestyle, bivalves have lost the head and the radular rasping organ typical of most mollusks.
Do bivalves have tentacles?
Most bivalves are filter feeders, using their gills to capture particulate food such as phytoplankton from the water. ... These primitive bivalves hold on to the substratum with a pair of tentacles at the edge of the mouth, each of which has a single palp, or flap.
Do bivalves feel pain?
In addition, as we will discuss, bivalves have the ability to close their shells to avoid sources of harm, and feeling pain (which requires sentience) could allow them to do so in appropriate circumstances.
Are bivalves Monoecious or dioecious?
Sexes of bivalves can be separate (dioecious) or hermaphroditic (monoecious). The gonad may be a conspicuous, well defined organ as in scallops or occupy a major portion of the visceral mass as in clams.
Do bivalves have gills?
Like fish, bivalve mollusks breathe through their gills. As filter feeders, bivalves gather food through their gills. Some bivalves have a pointed, retractable "foot" that protrudes from the shell and digs into the surrounding sediment, effectively enabling the creature to move or burrow.
Is an octopus a bivalve?
includes clams, snails, slugs, nudibranchs, squid, octopuses, tusk shells, chitons, and many others that are all generally called mollusksMollusk: ... A member of the phylum Mollusca; also spelled mollusc (most especially in the United Kingdom)..
Do bivalves have a mantle?
The mantle cavity functions as a respiratory chamber in most mollusks. In bivalves it is usually part of the feeding structure. In some mollusks the mantle cavity is a brood chamber, and in cephalopods and some bivalves such as scallops, it is a locomotory organ. The mantle is highly muscular.
How do bivalves burrow?
Burrowing in bivalves involves foot,shell and siphons. These which operate in sequence to bring about downward movement. ... This is immediately followed by contraction of foot retractor muscles, pulling the bivalve downward towards the anchored foot.
What type of fossil is a bivalve?
Fossil bivalves were formed when the sediment in which they were buried hardened into rock. Many closely resemble living forms which helps us to understand how they must have lived. Bivalves have two hard, usually bowl-shaped, shells (called valves) enclosing the soft body.
