Worm. The term worm /ˈwɜrm/ refers to an obsolete taxon (vermes) used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm.
Currently it is used to describe many different distantly related animals that typically have a long cylindrical tube-like body and no legs. Most animals called "worms" are invertebrates, but the term is also used for the amphibian caecilians and the slow worm Anguis, a legless burrowing lizard. Annelid. Although many species can reproduce asexually and use similar mechanisms to regenerate after severe injuries, sexual reproduction is the normal method in species whose reproduction has been studied.
The minority of living polychaetes whose reproduction and lifecycles are known produce trochophore larvae, which live as plankton and then sink and metamorphose into miniature adults. Oligochaetes are full hermaphrodites and produce a ring-like cocoon round their bodies, in which the eggs and hatchlings are nourished until they are ready to emerge. Earthworms support terrestrial food chains both as prey and by aerating and enriching soil.
The burrowing of marine polychaetes, which may constitute up to a third of all species in near-shore environments, encourages the development of ecosystems by enabling water and oxygen to penetrate the sea floor. In addition to improving soil fertility, annelids serve humans as food and as bait. Earthworm. An earthworm is a tube-shaped, segmented animal commonly found living in soil, that feeds on live and dead organic matter.
Its digestive system runs through the length of its body. It conducts respiration through its skin. An earthworm has a double transport system composed of coelomic fluid that moves within the fluid-filled coelom and a simple, closed blood circulatory system. It has a central and a peripheral nervous system. The central nervous system consists of two ganglia above the mouth, one on either side, connected to a nerve cord running back along its length to motor neurons and sensory cells in each segment. Earthworms are hermaphrodites—each individual carries both male and female sex organs. "Earthworm" is the common name for the largest members of Oligochaeta (which is either a class or a subclass depending on the author) in the phylum Annelida. Nematode. Habitats[edit] Nematodes have successfully adapted to nearly every ecosystem from marine to fresh water, to soils, and from the polar regions to the tropics, as well as the highest to the lowest of elevations.
Flatworm. In traditional zoology texts, Platyhelminthes are divided into Turbellaria, which are mostly nonparasitic animals such as planarians, and three entirely parasitic groups: Cestoda, Trematoda and Monogenea; however, since the turbellarians have since been proven not to be monophyletic, this classification is now deprecated.
Polychaete. The Polychaeta or polychaetes are a polyphyletic[1] class of annelid worms, generally marine.
Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000 species are described in this class. Common representatives include the lugworm (Arenicola marina) and the sandworm or clam worm Nereis. Description[edit] Polychaetes are segmented worms, generally less than 10 cm (3.9 in) in length, although ranging at the extremes from 1 mm (0.039 in) to 3 m (9.8 ft).
However, polychaetes vary widely from this generalised pattern, and can display a range of different body forms. Nemertea. Nemertea is a phylum of invertebrate animals also known as "ribbon worms" or "proboscis worms".[3] Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela.[2] Although most are less than 20 centimetres (7.9 in) long, one specimen has been estimated at 54 metres (177 ft), which would make it the longest animal ever found.[4] Most are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies.
Many have patterns of yellow, orange, red and green coloration. In most species the sexes are separate, but all the freshwater species are hermaphroditic. Nemerteans often have numerous temporary gonads (ovaries or testes), and build temporary gonoducts (ducts from which the ova or sperm are emitted), one per gonad, when the ova and sperm are ready. The eggs are generally fertilised externally. Some species shed them into the water, and others protect their eggs in various ways. History[edit] Chaetognatha. There are more than 120 modern species assigned to over 20 genera.[2] Despite the limited diversity of species, the number of individuals is large.[3] Anatomy[edit] Chaetognaths are transparent or translucent dart-shaped animals covered by a cuticle.
Lineus longissimus. The bootlace worm (Lineus longissimus) is one of the longest known animals, with specimens up to 55 metres (180 ft) long and up to 10 centimetres (3.9 in) wide being reported.
Its mucus is toxic.[1] Taxonomy[edit] The bootlace worm is in the phylum Nemertea or ribbon worms. It is the most common nemertean found along the coasts of Britain. Description[edit] They may grow as long as 55 metres (180 ft), which would make it the longest animal in the world. When handled it produces large amounts of thick mucus with a faint pungent smell. Like other nemerteans, Lineus longissimus feeds using its eversible proboscis.