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. Invertebrate animals commonly called "worms" include annelids (earthworms), nematodes (roundworms), platyhelminthes (flatworms), marine polychaete worms (bristle worms), marine nemertean worms ("bootlace worms"), marine Chaetognatha (arrow worms), priapulid worms, and insect larvae such as caterpillars, grubs, and maggots.
Historical English-speaking cultures have used the (now deprecated) terms worm, Wurm, or wyrm to describe carnivorous reptiles ("serpents"), and the related mythical beasts dragons. 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. Since annelids are soft-bodied, their fossils are rare – mostly jaws and the mineralized tubes that some of the species secreted. Prostomium O Anus. 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.
Large numbers of chemoreceptors are concentrated near its mouth. Circumferential and longitudinal muscles on the periphery of each segment enable the worm to move. Earthworms are hermaphrodites—each individual carries both male and female sex organs. Earthworms are far less abundant in disturbed environments and are typically active only if water is present.[3] Anatomy.
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. They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as mountains, deserts and oceanic trenches. They are found in every part of the earth's lithosphere.[5] They represent, for example, 90% of all life forms on the ocean floor.[6] Their numerical dominance, often exceeding a million individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity of life cycles, and their presence at various trophic levels point at an important role in many ecosystems.[7] Their many parasitic forms include pathogens in most plants and animals (including humans).[8] Some nematodes can undergo cryptobiosis.
Anatomy[edit] 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. Free-living flatworms are mostly predators, and live in water or in shaded, humid terrestrial environments such as leaf litter. Cestodes (tapeworms) and trematodes (flukes) have complex life-cycles, with mature stages that live as parasites in the digestive systems of fish or land vertebrates, and intermediate stages that infest secondary hosts. The eggs of trematodes are excreted from their main hosts, whereas adult cestodes generate vast numbers of hermaphroditic, segment-like proglottids which detach when mature, are excreted, and then release eggs. Over half of all known flatworm species are parasitic, and some do enormous harm to humans and their livestock.
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. The head, or prostomium, is relatively well developed, compared with other annelids. Internal anatomy and physiology[edit] General anatomy of a polychaete The outer surface of the body wall consists of a simple columnar epithelium covered by a thin cuticle. Ecology[edit] 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] Description[edit] 1: Proboscis 7: Mouth. 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.
The body is divided into a distinct head, trunk, and tail. There are between four and fourteen hooked, grasping spines on each side of their head, flanking a hollow vestibule containing the mouth. The spines are used in hunting, and covered with a flexible hood arising from the neck region when the animal is swimming. Chaetognaths swim in short bursts using a dorso-ventral undulating body motion, where their tail fin assists with propulsion and the body fins for stabilization and steering.[7] Some species are known to use the neurotoxin tetrodotoxin to subdue prey.[8] The mouth opens into a muscular pharynx, which contains glands to lubricate the passage of food. Materials are moved about the body cavity by cilia. Reproduction[edit] 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.
Habitat[edit] Lineus longissimus can be found on sandy shores, muddy shores, and in tide pools. References[edit] External links[edit]