miracidium is a larval stage in the development of trematode.
miracidium is a larval stage in the development of trematode.
miracidium is a larval stage in the development of?
trematode
the life cycle of "f. magna" is relatively complex and is similar to the development of the related fluke, "f. hepatica". a detailed account of the "f. magna" life cycle was given by swales (1935), erhardová-kotrlá (1971), and reviewed by pybus (2001).adult flukes occur in pairs or groups within a fibrous capsule in the liver parenchyma of the definitive host. mature flukes release eggs which are collected in the cavity of the capsule. the capsule contains a great mass of eggs and has duct connections to bile ducts. the eggs are passed together with bile into the bile collecting system, enter the small intestine, and leave the definitive host along with the faeces. the eggs which are passed out in the faeces into the environment are undeveloped and undergo embryonation outside the host. several physical-chemical factors, especially temperature, humidity and oxygen tension, are known to influence embryonation. during the embryonation of the egg, a larva called a miracidium develops from germinal cells. fully developed miracidium releases the operculum of the egg using several proteases. the embryonation period varies from 27 to 44 days in natural conditions. ciliated miracidia hatch in water and actively seek suitable intermediate hosts that are freshwater snails from family lymnaeidae. after attaching to a suitable snail host, the miracidium penetrates into the snail body. after shedding its ciliated cell layer it is called a sporocyst. the sporocysts are found in the foot, the snail body, digestive glands, reproductive organs, and in the pulmonary sac of the snail. the sporocysts contain germinal cells that give rise to 1-6 mother rediae (a trematode larval form with an oral sucker). developed mother rediae are released from the sporocyst and migrate into digestive glands, renal organ, reproductive organs, and pulmonary sac of the snail body. each mother redia can asexually produce up to 10 daughter rediae. however, only 3 to 6 daughter rediae complete their development and leave the mother rediae. in turn, each daughter redia may produce 1-6 trematode lifecycle stages#typical lifecyle stagescercariae in experimentally infected snails and 16-22 cercariae under natural conditions. cercariae emerge from the rediae and mature usually in digestive glands of the snail. mature cercarie spontaneously emerge from the snail host and swim actively in water for up to two hours before encysting on vegetation. after encystment the flukes are called metacercariae. development within the snail takes 40 to 69 days depending upon the temperature and the species of snail. the definitive host ingests vegetation containing the metacercariae. in the stomach and the intestine, the metacercariae are stimulated to emerge from the cyst (excystation). newly excysted juvenile flukes penetrate the wall of the intestine and migrate in the abdominal cavity. juvenile flukes penetrate the glisson’s capsule of the liver and continue migrating in the liver tissue. rarely juvenile flukes penetrate other organs, such as lungs or kidneys. in these organs, however, flukes do not survive and not attain maturity. in the liver, flukes migrate within the parenchyma to search another fluke. if the fluke meet another one, they stop moving, and the fibrous capsule is formed around them. in the capsule, the parasite completes its development and starts egg-laying. prepatent period varies 3–7 months and is dependent on host species. adult "f. magna" can survive in the liver of the host up to 7 years.
fascioloides magna
the southern brook lamprey's life cycle consists of two main stages: larval and adult. during the larval stage, the southern brook lamprey inhabits a distinct micro habitat involving relatively slow moving water and a sandy substrate. the consistency of the substrate is vitally important to the southern brook lamprey because during the larval stage, the southern brook lamprey burrows into the substrate using its oral disk as an anchor. the southern brook lamprey secretes mucus from its body to form a tube leading to the entrance of the burrow and to provide support for the burrow. the formation of this larval burrow relies on the composition and size of the substrate available. the combination of both small and large particles and coarse and fine sand grains allow the southern brook lamprey to construct a suitable burrow that allows enough water to flow through the burrow to ensure proper respiration. the substrate in which larval southern brook lamprey burrow must not contain too many fine silt and clay particles as this would inhibit respiration while too many particles of coarse sand would hinder proper burrow construction. the larval stage is complete after approximately three years. following the larval stage, the southern brook lamprey undergoes metamorphosis into the adult form. adult southern brook lamprey are found in crevices and cracks between large rocks in deeper, faster moving water than the habitat occupied during the larval stage. after completing the metamorphosis to adults, southern brook lampreys come together in groups to spawn and, once spawning is complete, the adults die. spawning usually occurs between april and may and takes place in another distinct microhabitat consisting of shallow riffle areas with rocky substrate with a water temperature falling between 17 °c to 21 °c. fecundity of the southern brook lamprey averages between 800 and 2500 oocytes. human factors have been found to influence the available habitat for spawning southern brook lampreys. southern brook lampreys have been recorded using shallow areas under bridges as spawning grounds possibly to help conceal spawning aggregations from visual predators.
southern brook lamprey