Tubifex - Copulation and Cocoon Formation

Copulation and Cocoon Formation

Although the Tubifex worms are hermaphrodites, the male and female organs become mature at different times; thus self-fertilization is avoided, and cross-fertilization is encouraged. Two mature Tubifex worms undergo copulation by joining their ventral and anterior surfaces together with their anterior ends pointing opposite directions. Thus, the spermathecal openings of each worm is nearer to the male apertures of another worm. The penial setae of one worm penetrate into the tissues of other worm and thus the conjugants are held together. At this stage, the sperm of one worm is passed into the spermathecae of the other worm. After copulation, they separate and begin to produce egg cases containing eggs, called cocoons. The cocoon is formed around the clitellum as a soft, box-like structure into which the ova and the sperm are deposited. Soon, the Tubifex worm withdraws its body from the egg case by its backward wriggling movements. As the worm withdraws, the cocoon completely closes and becomes a round-shaped case containing both sperm cells and ova. Fertilized eggs form in the cocoon, and undergo complete development in the using the case's albuminous nutritive fluid for growth. The period of development varies with temperature and lasts for two to three weeks. After complete development, the young worms emerge.