Atrium (heart)
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The atrium is one of the two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular mitral and tricuspid heart valves.
Right heart anatomy, right ventricle seen on right of illustration
Left atrial appendage shown at upper right
CT scan of the chest showing a thrombus in the left atrial appendage (left: axial plane, right: coronal plane)
Mollusca
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Mollusca is the second-largest phylum of invertebrate animals, after Arthropoda; members are known as molluscs or mollusks. Around 76,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.
Image: Grapevinesnail 01a
Image: Octopus 2
Image: Clams on Sandy Hook beaches panoramio
Image: Tonicella lineata