Earthworm 20D0047828

Earthworm (Lumbricus terrestris)
Wikipedia: [link]

Earthworm is the usual name for the largest members of Oligochaeta in the phylum Annelida. Folk names for the earthworm include "dew-worm", "rainworm", "night crawler" and "angleworm" (due to its use as fishing bait).

Anatomy
Earthworms have a simple circulatory system. They have two main blood vessels that extend through the length of their body: a ventral blood vessel which leads the blood to the posterior end, and a dorsal blood vessel which leads to the anterior end. A typical lumbricid will have 5 pairs of hearts. Earthworms eat in a unique way: their mouth cavity connects directly into the digestive tract without any intermediate processes. Most earthworms are decomposers feeding on undecayed leaf and other plant matter, others are more geophagous.

Reproduction
Earthworms are hermaphrodites (both female and male organs within the same individual). They have testes, seminal vesicles and pores which produce, store and release the sperm, and ovaries and ovipores. Some species use external spermatophores for transfer instead. Copulation and reproduction are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The cocoon, or egg case, is secreted by the clitellum, the external glandular band which is near the front of the worm, but behind the spermathecae. Some time after copulation, long after the worms have separated, the clitellum secretes the cocoon which forms a ring around the worm. The worm then backs out of the ring, and as it does so, injects its own eggs and the other worm's sperm into it. As the worm slips out, the ends of the cocoon seal to form a vaguely lemon-shaped incubator (cocoon) in which the embryonic worms develop. They emerge as small, but fully formed earthworms, except for a lack of the sexual structures, which develop later in about 60 to 90 days. They attain full size in about one year. Several common earthworm species are mostly parthenogenetic, that is, with asexually reproduction resulting in clones.

Regeneration
Earthworms have the facility to replace or replicate lost segments, but this ability varies between species and depends on the extent of the damage. It is theoretically possible to grow two whole worms from a bisected specimen in certain species (but don't try this at home!).