- Some annelids reproduce asexually and others reproduce sexually
- However some do both, often the worm will be asexually in the summer and sexually in autumn
- When they reproduce asexually they do it by dividing themselves into two or more pieces
- Otherwise they have sex with a member of the opposite sex even though they all have both reproductive systems
- Many annelids have both the female reproductive system and the male reproductive system or they change throughout their lives
- Other times they just act one sex for their entire life
- Some breed only once in their lives while others breed continuously throughout their lives
- Earthworms store their partners' sperm in spermathecae and then the clitellum produces a cocoon that collects ova from the ovaries and then sperm from the spermathecae
- Fertilization and development of earthworm eggs takes place in the cocoon however Leeches' eggs are fertilized in the ovaries, and then transferred to the cocoon
- They all hatch as miniature adults rather than larvae
- The Leeches are the only annelids that have never been seen reproducing asexually