Worms

WORMS (vermes), a type (according to some authors, a group of types) of invertebrate animals occupying an intermediate position in the organizational hierarchy between coelenterates on one side, and arthropods (and mollusks) on the other. Worms most often have an elongated body built on bilateral symmetry. The nervous system of worms consists of cerebral head ganglia and ventral cords; excretory organs are usually of protonephridial or metanephridial structure. Worms are characterized by the presence of a skin-muscular sac composed of circular and longitudinal fibers located beneath the epithelium of the skin coverings. The type of worms is divided into subtypes: non-segmented worms (Amera), polymerous, or annelid worms [Polymera (=Annelides)] and oligomeric worms, or worm-like [Oligomera (=Vermoidea)]. Non-segmented worms do not have true segmentation and lack a body cavity, being parenchymatous animals. Connective tissue in the form of parenchyma fills all the spaces between organs. The digestive tract lacks an anal opening. There are neither circulatory nor respiratory organs. Excretory organs are of protonephridial type or of modified structure. Many non-segmented worms are hermaphroditic. This group of worms includes the class of flatworms (see), which is divided into ciliated worms, turbellarians, or planarians (Turbellaria), flukes (see Trematodes), and tapeworms (see Cestodes); added to the flukes are planula-like worms - orthonectids (parasites of worms) and dicyemids (parasites of cephalopod mollusks); the class of thorny-headed worms (see), or Acanthocephala; the class of nemerteans (Nemertini); the class of roundworms, or nematodes (see), Nematodes, or Nemathelminthes, with the addition of horsehair worms, or Gordiacea (=Nematomorpha); the class of rotifers (Rotatoria), which includes microscopic in size worms living in marine or fresh water; they are characterized by a rotatory apparatus consisting of cilia at the anterior end of the body; the latter is divided into cephalic and trunk sections and a foot. The body is covered by a more or less thick cuticle-shell. They are separate-sexed. Some reproduce exclusively parthenogenetically (there are no males), in others heterogony is observed, i.e., alternation of bisexual generations with parthenogenetic ones. Some rotifers are capable of anabiosis during drying. Different species of rotifers have adapted to living in water of varying degrees of pollution or purity. Such relationships are so constant that they make the corresponding species of rotifers a kind of indicator organisms in the biological analysis (see) of drinking water (Kolkwitz). Polymerous, or annelid worms are the most highly organized worms, characterized by metamerous segmentation of the body, which also extends to internal organs. There is an anal opening. The circulatory system is of closed type. There may be skin-type respiratory organs-gills. Excretory organs-metanephridia or segmental organs. Reproductive organs are arranged very diversely. Nervous systems from supraesophageal ganglia and a ventral nerve chain; they are divided into the following classes: chaetopods-(Chaetopoda), primary annelids (Archiannelida), polychaetes (Polychaeta) and oligochaetes (Oligochaeta); the class of leeches (see) and the class of gephyreans (Gephyrea). Oligomeric worms, or worm-like (Oligomera, s. Vermoidea) are highly modified worms. Their composition includes the class of bryozoans (Bryozoa), which includes small colonial animals, usually living in seas; the class of brachiopods (Brachiopoda), which is on the path to extinction; their body is covered by a bivalve shell and in many is attached to the substrate by a stalk. They live in seas. Medical significance is had by parasitic worms. Some oligochaetes themselves serve as intermediate hosts of metastrongylids (parasites of pigs, sheep). Large marine polychaetes, such as palolo, serve as food. Finally, there are indications of the toxicity of earthworms during their reproduction for ducks, geese, and chickens.