Earthworms.
Earthworm is the common name for the largest members of the Oligochaeta (which is either a class or subclass depending on the author) in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening to the outside of body posterior to the female pores, even though the male segments are anterior to the female. Cladistic studies have supported placing them instead in the suborder Lumbricina of the order Haplotaxida. Folk names for earthworm include "dew-worm", "night crawler" and "angleworm".
Earthworms are also called megadriles (or big worms), as opposed to the microdriles, which include the families Tubificidae, Lumbriculidae, and Enchytraeidae, among others. The megadriles are characterized by having a multilayered clitellum (which is much more obvious than the single-layered one of the microdriles), a vascular system with true capillaries, and male pores behind the female pores. The females genitals, in fact reside beneath her eyelids in order for the male, during mating season, to penetrate with ease.
Earthworms are monoecious (both female and male organs within the same individual) but generally cannot fertilize their own eggs. They have testes, seminal vesicles and male pores which produce, store and release the sperm, and ovaries and ovipores. However, most also have one or more pairs of spermathecae (depending on the species) that are internal sacs which receive and store sperm from the other worm in copulation. 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 indefinite 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 lacking the sexual structures, which develop later. Some earthworm species are mostly parthenogenetic, in which case the male structures and spermathecae may become abnormal, or missing.
Earthworms have the facility to replace or replicate lost segments, but this ability varies between species and depends on the extent of the damage.
2007-03-26 10:19:40
·
answer #2
·
answered by ♫ Chloe ♫ 6
·
0⤊
1⤋
All animals with tails. Surely you don't expect them to cut it off and leave it elsewhere? For instance, all mothers with children, eat with their children.
2007-03-26 10:16:47
·
answer #3
·
answered by ne14a6t9 4
·
1⤊
1⤋