In Chinese mythology, the shen or chen () is a shapeshifting dragon or shellfish-type sea monster believed to create mirages.
The Chinese classics use the word shèn to mean "a large shellfish" that was associated with funerals and "an aquatic monster" that could change its shape, which was later associated with "mirages".
The word used to mean a shellfish, or mollusk, identified as an oyster, mussel, or giant clam such as the Pearl of Lao Tzu. While early Chinese dictionaries treat shèn as a general term for "mollusca", the Erya defines it as a large yáo () "shellfish", "clam", "scallop", or "nacre". The Shuowen Jiezi, an early second-century dictionary of the Eastern Han, defines it a large gé (), meaning "clam", "oyster", "shellfish", or "bivalve".
Chinese classics variously record that shèn was salted as a food (in the Zuo Zhuan), named a "lacquered wine barrel" used in sacrifices to earth spirits (in the Rites of Zhou), and its shells were used to make hoes (in the Huainanzi) and receptacles (in the Zhuangzi). They also record two shèn-compounds related with funerals: shènchē (, with cart or carriage) "hearse" (Rites of Zhou, Guo Pu's commentary notes shèn means large, shell-like wheel rims) and shèntàn () "oyster-lime; white clay", which was especially used as mortar for mausoleum walls (Zuo Zhuan, Rites of Zhou).
Wolfram Eberhard describes the shèn mussel as "a strange animal", and mentions the Rites of Zhous zhǎngshèn () "manager of shèn", who was a special government official in charge of acquiring them for royal sacrifices and funerals. "It is not clear why these mussels were placed into the tombs," he admits, possibly either as a sacrifice to the earth god (compare shèn below) or "the shell lime was used simply for a purifying and protective effect."
Edward H. Schafer, who translates shèn as "clam-monster", traces its linguistic evolution from originally designating a "large bivalve mollusc":
Beginning as an unassuming marine invertebrate, the ch'en was later imagined as a gaping, pearl-producing clam, possibly to be identified with the giant clams of tropical seas, for instance Tridacna.