ECOLOGY & HABITATS
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The shell divide into two valves related to the adaption of burrowing mode of life.
Primary form of early bivalves were detritivorous while, modern bivalves are filterfeeders.
Bivalves are limited to aquatic environments due to their burrowing and filter-feeding
mode of life.
 The adult retention of the larval anchoring byssus has freed many bivalves from soft
substrates, allowing them to colonise hard surfaces.
 There are no pelagic bivalves except Planktomya hensoni.
 Planktomya hensoni still benthic as an adult but has a usually long planktonic larval
stage.
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When separated from sediment, some bivalves can swim although weakly.
Swimming bivalves however only seen in the family Pectinidae (scallops).
Most bivalves are found in coastal seas but their diversitiy is greatest on continential
landmasses.
A few bivalves also found on islands.
o Subclasses Heterodonta are feed predominatly on suspended material (modern
bivalves).
o Example: cockles, clams, & shipworms.
o Subclasses Petriomorphia which is epibyssate and dominates hard substrates.
o Example: oysters, mussels, & jingle shells.
o Some of their species are endobyssate.
o Most representative use simple reproductive strategies which is external and
planktonic larvae.
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Palaeoheterodonta are all freshwater species and their life cycles are substantially
complicated.
Palaeotaxodonta (protobranchia) are coastal and deep-water detrivores.
Both share the diversity of habitat with Anomalodesmata species.
Most bivalves are primarily consumers which exploiting organic material.
The two dominant subclasses of bivalves also high in diet of many predators.
Adaptive radiation in the bivalves took place in similar radiation in predator’s habitats.
The predation pressure effectively drove the bivalves underground, resulting in the
creation of multiple antipredation devices od shell spines, or teeth.
 Or even the habit of burrowing to vast depths.
GENERAL FEATURES
The bivalve body is made up of a dorsal visceral mass and a ventral foot that is surrounded
by a thin mantle, or pallium.
 The mantle secretes a shell separated into left and right valves from its outer
surface.
 Between the body and mantle is the mantle cavity, within which hang the left and
right gills.
 The ctenidia are split into two demibranchs, inner and outer.
 The ctenidia connect anteriorly with paired (left and right) labial palps.
 The mantle edge can be fused at various points, leaving medial openings anteriorly
for locomotory foot extension and retraction.
 Foot and siphons can be withdrawn between the shell valves into the mantle cavity
for protection.