Each miracidium goes through several developmental stages inside the snail: firstly into a series of daughter cells called sporocysts and then into rediae, which give rise to many worm-like larvae called cercariae. The cercariae penetrate through the body of the snail, emerging into the water. Development in the snail takes about 9 to 13 weeks.The cercariae then infect the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. Encystment occurs in the liver, gills, intestine, skeletal muscles and sometimes in the heart. These cysts are the infective stage for the mammalian host. Freshwater crab species of genera Potamiscus, Potamon, Paratelphusa, Eriocheir, Geothelphusa, Barytelphusa, crayfish species of genus Camberoides and shrimps of genera Acrohrachium and Caridina commonly serve as the secondary intermediate hosts. The secondary intermediate hosts are infected either by directly eating the snail or penetration of the body by free-swimming cercariae.Human infection with P. westermani — the best understood species — occurs by eating inadequately cooked or pickled crab or crayfish that harbour metacercariae of the parasite. The metacercariae excyst in the duodenum, penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5 to 12 mm by 4 to 6 mm). Unlike most other trematodes, after they migrate from the intestine, they remain in the peritoneal cavity until they find a suitable partner. Only then do the couples enter the lung tissues to form capsules.
Caput succedaneum is a neonatal condition involving a serosanguinous, subcutaneous, extraperiosteal fluid collection with poorly defined margins caused by the pressure of the presenting part of the scalp against the dilating cervix (tourniquet effect of the cervix) during delivery.It involves bleeding below the scalp and above the periosteum. See also
Cephalohematoma
Cephalic
Chignon (medical term)
Hematoma
Subgaleal hemorrhage

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