4/29/2023 0 Comments Leech eggsThe gametes, especially eggs, are nourished by the breakdown products of muscle tissue, which are passed on to the gametes via the eleocytes. The developing gametes are shed into the coelom, where they are nourished by nurse cells (eleocytes). Gametes are derived from the mesodermal linings around the digestive tract. In the polychaetes, sexes are usually separate but cannot be distinguished in the immature state until gametes (eggs and sperm) appear. Reproductive parts of the palolo ( Palola siciliensis), which break off and are found in great numbers during the reproductive period, are used as food in Samoa in the south Pacific. The estuarine flats of Maine and Nova Scotia are the principal sources of the bloodworm ( Glycera dibranchiata), which is used as bait for saltwater fishes. Hirudin, an extract from leeches, is used as a blood anticoagulant. The European species Hirudo medicinalis formerly was exported throughout the world, and native species also were used. The medicinal use of leeches, which dates from antiquity, reached its peak in the first half of the 19th century. Polychaetes play an important role in turning over sediment on the ocean bottom. The sludge worm Tubifex, abundant near sewer outlets and thus an indicator of water pollution, is collected and sold as food for tropical fish. Large earthworms, or night crawlers ( Lumbricus terrestris), are cultivated and sold as bait for freshwater fishes and as humus builders in gardens. The poorly developed eyes are paired structures at the anterior end. A clitellum is present in the mid-region during the reproductive period. Leeches have a small sucker at the anterior end and a large sucker at the posterior end. Leeches have 34 segments, and elongation occurs by the subdivision of these segments. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.
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