A few leeches are found in saltwater; a few terrestrial (land) leeches are found in moist, damp locations.  Body fossils going back to the mid Ordovician, from 472 to 461 million years ago, have been tentatively classified as oligochaetes, but these identifications are uncertain and some have been disputed. The body does not contain parapodia, tentacles,and setae. In the glaciated areas of North America, for example, almost all native earthworms are thought to have been killed by the glaciers and the worms currently found in those areas are all introduced from other areas, primarily from Europe, and, more recently, from Asia. The body is elongated with no prostomial appendages.  A trace fossil consisting of a convoluted burrow partly filled with small fecal pellets may be evidence that earthworms were present in the early Triassic period from 251 to 245 million years ago.  Burrowing species increase the penetration of water and oxygen into the sea-floor sediment, which encourages the growth of populations of aerobic bacteria and small animals alongside their burrows. Among them, Polychaetes constitute about 12,000 species while Clitellates contains about 10,000 species. They can survive in various ecological conditions, some live in marine environments, others live in fresh water, and yet others can live in moist terrestrial environments. Inland waters of the Nearctic are home to many free-living aquatic worms (Oligochaeta), ectoparasitic and predaceous leeches (Hirudinida), and ectosymbiont crayfish worms (Branchiobdellidea). It has two openings. While most polychaetes remain of one sex all their lives, a significant percentage of species are full hermaphrodites or change sex during their lives.  Most annelids have closed circulatory systems, where the blood makes its entire circuit via blood vessels. They are marine polychaete worms which are found worldwide. Some annelids like leeches are harm to other animals due to their blood-sucking behavior. In these animals the foremost few segments often lack septa so that, when the muscles in these segments contract, the sharp increase in fluid pressure from all these segments everts the pharynx very quickly. amzn_assoc_default_category = "PCHardware"; Stauronereis incertus, Lumbineris flabellicola, Examples: Scoloplos armiger, Paraonis fulgens, Example: The simplest are unjointed and form paired bundles near the top and bottom of each side of each segment. B stomach . In this case, prostomium contains distinct head which bears tentacles, eyes etc. Head bears 0 to 7 antennae which are usually smooth but occasionally jointed. Example: View Answer Discuss. They have closed type blood vascular system. , Feeding structures in the mouth region vary widely, and have little correlation with the animals' diets. 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. They have relatively stout, slightly flattened body. , The gut is generally an almost straight tube supported by the mesenteries (vertical partitions within segments), and ends with the anus on the underside of the pygidium. Annelids exhibit bilateral symmetry and ar… amzn_assoc_title = "Shop Your Products"; 1; 2; 3 » Question No : 1 A chitinous lining in earthworm is found in . Body lacks parapodia but numerous small setae arise from setigerous which act as the locomotory organ.  The mesothelium is made of modified epitheliomuscular cells; in other words, their bodies form part of the epithelium but their bases extend to form muscle fibers in the body wall. Spio filicornis, Polydora cornuta, Examples: Chaetopterus variopedatus (parchment worm or parchment tube worm ), Spiochaetopterus typicus etc, Examples: Psammodrilus fauveli, Psammodrilus balanoglossoides, Examples: amzn_assoc_ad_mode = "search"; amzn_assoc_default_search_phrase = "shoes"; They have an elongated, segmented body with a distinct head. The rest care for the fertilized eggs until they hatch – some by producing jelly-covered masses of eggs which they tend, some by attaching the eggs to their bodies and a few species by keeping the eggs within their bodies until they hatch.  The small shelly fossil Cloudina, from 549 to 542 million years ago, has been classified by some authors as an annelid, but by others as a cnidarian (i.e. Leeches often have an eversible proboscis, or a muscular pharynx with two or three teeth. Oligochaeta – earthworms, etc. The size of body ranges from 0.5 to 35 cm. They are primarily live in freshwater, few in sea and other on moist land. 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