Final answer:
The hard parts of clams are most likely to be preserved as fossils. Soft parts rarely survive the fossilization process due to their rapid decay, and complete fossil preservation including soft parts is extremely rare.
Step-by-step explanation:
When it comes to preservation, it is the hard parts of bivalves, which include clams, scallops, oysters, and mussels, that are more likely to be fossilized. These organisms have a shell composed of two parts that can open and close, which offers a durable structure capable of surviving long-term geological processes. The soft parts, such as the mouth, heart, intestine, gills, and stomach, typically decay and are rarely preserved; however, there are exceptional occurrences where conditions permit the preservation of soft tissues, as seen with some belemnite fossils, though this is extremely rare.
The alteration of hard parts is a common occurrence in fossil records, resulting in fossil preservation such as permineralization, recrystallization, replacement, carbonization, or dissolution. These processes affect the skeletal material of the hard parts, making them the principal components discovered in fossil records.