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Annelids
The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments. The annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. They also have parapodia for locomotion. Most textbooks still use the traditional division into polychaetes (almost all marine), oligochaetes (which include earthworms) and leech-like species. Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-group ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leech
Leeches are segmented parasitism, parasitic or Predation, predatory worms that comprise the Class (biology), subclass Hirudinea within the phylum Annelida. They are closely related to the Oligochaeta, oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodies that can lengthen and contract. Both groups are hermaphrodites and have a clitellum, but leeches typically differ from the oligochaetes in having suckers at both ends and ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid; the coelom, the spacious body cavity found in other annelids, is reduced to small channels. The majority of leeches live in freshwater habitats, while some species can be found in terrestrial or marine environments. The best-known species, such as the medicinal leech, ''Hirudo medicinalis'', are hematophagous, attaching themselves to a host with a sucker and feeding on blood, having first secreted the pepti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hirudinea
Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodies that can lengthen and contract. Both groups are hermaphrodites and have a clitellum, but leeches typically differ from the oligochaetes in having suckers at both ends and ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid; the coelom, the spacious body cavity found in other annelids, is reduced to small channels. The majority of leeches live in freshwater habitats, while some species can be found in terrestrial or marine environments. The best-known species, such as the medicinal leech, ''Hirudo medicinalis'', are hematophagous, attaching themselves to a host with a sucker and feeding on blood, having first secreted the peptide hirudin to prevent the blood from clotting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myzostomida
The Myzostomida or Myzostomatida are an order of small marine (ocean), marine worms, which are Parasitism, parasitic on echinoderms, mostly crinoids. These highly unusual and diverse annelids were first discovered by Friedrich Sigismund Leuckart in 1827. Morphology A typical myzostomid has a flattened, rounded shape, with a thin edge drawn out into delicate radiating hairs called Cilium, cirri. The dorsal surface is smooth, with five pairs of Parapodium, parapodia on the bottom surface. These parapodia are armed with supporting and hooked setae, by means of which the worm adheres to its host. Beyond the parapodia are four pairs of organs, often called suckers. These organs are probably of sensory nature, and are comparable to the lateral sense organs of capitellids. The mouth and cloacal opening are generally at opposite ends of the bottom surface. The former leads to a protrusible pharynx, from which the esophagus opens into a wide intestinal chamber with branching lateral Di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echiura
The Echiura, or spoon worms, are a small group of ocean, marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into Segmentation (biology), segments, but echiurans have secondarily lost their segmentation. The majority of echiurans live in burrows in soft sediment in shallow water, but some live in rock crevices or under boulders, and there are also deep sea forms. More than 230 species have been described. Spoon worms are cylindrical, soft-bodied animals usually possessing a non-retractable proboscis which can be rolled into a scoop-shape to feed. In some species the proboscis is ribbon-like, longer than the trunk and may have a forked tip. Spoon worms vary in size from less than a centimetre in length to more than a metre. Most are deposit feeders, collecting detritus from the sea floor. Fossils of these worms are seldom found and the earliest known fossil specimen is from the Darriwilian, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Capitellida
Capitellida is an order of marine sedentarian annelids The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario .... Capitellida contains the following families: * Arenicolidae Johnston, 1835 * Capitellidae Grube, 1862 * Maldanidae Malmgren, 1867 References Annelids {{Annelid-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oligochaeta
Oligochaeta () is a subclass of soft-bodied animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadrile earthworms (some of which are semiaquatic or fully aquatic), and freshwater or semiterrestrial microdrile forms, including the tubificids, pot worms and ice worms ( Enchytraeidae), blackworms ( Lumbriculidae) and several interstitial marine worms. With around 10,000 known species, the Oligochaeta make up about half of the phylum Annelida. These worms usually have few setae (chaetae) or "bristles" on their outer body surfaces, and lack parapodia, unlike polychaeta. Diversity Oligochaetes are well-segmented worms and most have a spacious body cavity (coelom) used as a hydroskeleton. They range in length from less than up to in the 'giant' species such as the giant Gippsland earthworm (''Megascolides australis'') and the Mekong ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clitellata
The Clitellata are a class of annelid worms, characterized by having a clitellum – the 'collar' that forms a reproductive cocoon during part of their life cycles. The clitellates comprise around 8,000 species. Unlike the class of Polychaeta, they do not have parapodia and their heads are less developed. Characteristics Clitellate annelids are segmented worms characterised by the clitellum or girdle which is located near the head end of mature individuals. The mouth is on the ventral surface and is overhung by the prostomium (proboscis). The brain is not located in the head but in one of the body segments. The clitellum is formed by a modification of several segments, and either includes the female gonopores or is located just behind them. During copulation, this glandular tissue secretes mucus that keeps the paired individuals together while they exchange sperm. Afterwards it secretes material that forms a cocoon that encircles the animal's body and encloses the eggs and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sedentaria
Sedentaria is a diverse clade of annelid worms. It is traditionally treated as a subclass of the paraphyletic class Polychaeta, but it is also a monophyletic group uniting several polychaetes and the monophyletic class Clitellata. It is the sister group of Errantia. Sedentaria are mainly found within marine environments that have low oxygen levels and are specially adapted to these low oxygen environments by increasing gill surface area and having high-affinity respiratory proteins. Furthermore, they go through a process of metabolic depression which lowers their energy use so that they can inhibit these low oxygen zones . Phylogeny The phylogeny of polychaetes is slowly being resolved. Sedentaria and Errantia are the two biggest clades of polychaetes, and together they compose clade Pleistoannelida. Sedentaria's most basal clade is Orbiniida. Other groups that are nested within Sedentaria are: Clitellata, the Sabellida/ Spionida clade, Opheliida, Echiura, Cirratulifor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sabellida
Sabellida is an order of annelid worms in the class Polychaeta. They are filter feeders with no buccal organ. The prostomium is fused with the peristomium and bears a ring of feathery feeding tentacles. They live in parchment-like tubes made of particles from their environment such as sand and shell fragments cemented together with mucus. Members of the suborder include the feather duster worms (Sabellidae) and serpulid worms (Serpulidae). Among the species are the giant feather duster worm ('' Eudistylia polymorpha''), the peacock worm ('' Sabella pavonina''), the European fan worm ('' Sabella spallanzanii'') and the Christmas tree worm ('' Spirobranchus giganteus''). The inclusion of Oweniidae and Siboglinidae Siboglinidae is a family (biology), family of polychaete Annelida, annelid worms whose members made up the former phylum, phyla Pogonophora and Vestimentifera (the giant tube worms). The family is composed of around 100 species of vermiform creatu ... is not curre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Branchiobdellida
Branchiobdellida is an order of freshwater leech-like clitellates that are obligate ectosymbionts or ectoparasites, mostly of astacoidean crayfish. They are found in the Northern Hemisphere and have a holarctic distribution in East Asia, the Euro-Mediterranean region and North and Central America, with the greatest species diversity being in North and Central America. Taxonomy The exact relationship of this group of clitellates with other groups has been the subject of debate for a century or more. The American zoologist Perry C. Holt wrote his doctoral thesis on branchiobdellids and devoted his 45 years of research to the taxon. With his colleague, the American zoologist Richard L. Hoffman, he described 8 new genera and 75 new species, and re-described various other species. In 1965, he came to the conclusion that the group should be raised from a family to an order, a sister group to the oligochaetes and leeches. Forty years later, molecular data from rDNA and mitochond ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paraphyly
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In contrast, a monophyletic grouping (a clade) includes a common ancestor and ''all'' of its descendants. The terms are commonly used in phylogenetics (a subfield of biology) and in the tree model of historical linguistics. Paraphyletic groups are identified by a combination of synapomorphies and symplesiomorphies. If many subgroups are missing from the named group, it is said to be polyparaphyletic. The term received currency during the debates of the 1960s and 1970s accompanying the rise of cladistics, having been coined by zoologist Willi Hennig to apply to well-known taxa like Reptilia (reptiles), which is paraphyletic with respect to birds. Reptilia contains the last common ancestor of reptiles and all descendants of that ancest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
