Auxospore is

Auxospores or growth spores or rejuvenating spores are diploid spores of diatoms formed by the fusion of haploid gametes. These are formed during sexual reproduction when the size of cell due to binary fission reaches critical size, the cells show meiosis and form gametes. Gametes formed in different mother cells fuse and form diploid cells with normal size. Such cell are called as auxospores or growth spores.