Range in size from tiny They are bivalved (twoAlso called Pelecypoda seed shells 1-2mm in shelled) mollucs length to giant size Mostly are sedentary suspension feeders No head, no radula that depend on ciliary The heaviest bivalve and very little currents produced by was recorded at 300kg cephalizationthe gills to collect their food.
The shell are held together by a hinge ligament. Adductor muscles work in opposite to the hinge ligament. When the muscle relax the shell will be apart. Umbo is the oldest part of the shell which is projecting above the hinge ligament. The valves function largely for protection.
Mantle Folds forming excurrent and incurrent openings for feeding. Some have long, muscular part known as siphon for burrowing into mud. Equipped with cilia to direct water flow over gills for food and oxygen.Gills Present on both sides. Clad by mantle. Equipped with cilia also(same function as at mantle).Foot Attaches to visceral mass anteroventrally(at front and downside).
Eyes (ocelli) Steely blue in colour. Located at edge of mantle. Equipped with cornea, lens and retina.Organs Poor develop sense organs. Three pairs of separated ganglia.Heart Three-chambered heart. Pumps blood to gills and mantle for oxygenation, to kidney for eliminating waste.
Gland cells and labial palps secrete copiousaGill Oxygen and organic amounts of mucus material direct to the (entangles food gills particles suspended in water entering gills pores)
Ciliated tractsMouth move the particle- laden to the mouth
Step 3 The mucus & The suitable food particles are Enzymes from particles enters to kept whirling by a extracellular the digestiveStomach rotation digestion dissolve gland for gelatinous rod from it in layer intracellular (crysrtalline style) digestion.
Most bivalves move by extending their slender muscular foot between the valves. The foot The foot shorten Pump Longitudin swell and and pullblood into al muscle act as the the foot contract anchor animal forward Most bivalves use the foot for burrowing and a few creeping.
Oysters: Attach their shells to a surface by secreting cement. Mussels: Attach themselves by secreting a number of slender byssal threads. Scallops: Use their shells for locomotion by clapping the valves together to move in spurts.
Sexes usually separated. Fertilization usually external.Marine embryo through 3 free-swimming larval stage :TROCHOPORE, VELIGER LARVA & YOUNG SPAT.FRESHWATER CLAMS : fertilization is INTERNAL.Some gill tubes become temporary brood chambers.LAKES @ STREAM : attachment to fish prevent thesmall larvae from moved out of the lake or fartherdownstream.
If contact with Sinking to Glochidia Discharge fish, hitc the bottom d with hlike a to becomelarvae (specialize excurrent ride as sedentary d veligers) flow parasite adult. in the fish’s gills
Unique info » Some can produce pearl when foreign objects lodges(stays) in between shell and mantle. Mantle will secrete layers of nacre(calcium carbonate sheets) around the object as a protection layer. Pearl form when small spheres(shells of clams) are insert together while nacre was secreted.