Spermatid

Definition

A haploid, immature male gamete produced by the second meiotic division of a secondary spermatocyte. Spermatids undergo spermiogenesis—extensive morphological remodeling without further cell division—to differentiate into spermatozoa. In insects and arachnids, this process often involves dramatic elongation of the flagellar axoneme, mitochondrial reorganization into the nebenkern or mitochondrial derivatives, and nuclear condensation, producing the highly specialized sperm typical of many arthropod groups.

Etymology

From New Latin spermat-, sperm + -id (diminutive suffix indicating a developmental stage), analogous to spermatocyte.

Example

In Drosophila melanogaster, 64 spermatids remain interconnected by cytoplasmic bridges after meiosis, developing synchronously within a cyst; their flagella extend to lengths exceeding the male body before individualization releases mature sperm.

Synonyms

• haploid spermatogonium (obsolete usage, imprecise)

Related Terms

• Spermatocyte
• spermatogonium
• spermiogenesis
• spermatozoon
• sperm
• Meiosis
• Gonad
• Testis
• cytoplasmic bridge
• spermatodesm
• nebenkern

Usage Notes

Distinguish from spermatocyte (diploid cells undergoing meiosis) and spermatozoon (the terminally differentiated, motile gamete). The term spermatid specifically denotes the post-meiotic, pre-spermiogenic stage. In many insects, spermatids are conspicuously large or elongate during development, making them accessible experimental subjects for studying flagellar assembly and chromatin remodeling. Some literature uses 'spermatid' loosely for any pre-ejaculatory male germ cell; precise usage restricts it to the haploid stage following meiosis II.