What are the larval stages of trematode?
There are three distinct larval stages involved in all digenetic trematode life cycles: the miracidium, sporocyst, and cercaria. Some taxa also produce rediae and/or encysted metacercariae. All of these life stages except for the miracidium can be found in first intermediate hosts.
What is Redia larva?
Definition of redia : a larval form of a digenetic trematode (such as a liver fluke) that is produced within a sporocyst, has a mouth, pharynx, and gut, and contains cells which give rise to other rediae or to cercariae — see also redial entry 3.
How do the larval forms of the trematodes and the Cestodes differ?
Cestodes are tape-like and segmented in shape, have a head with suckers and possibly hooks, and lack a digestive tract. Trematodes are leaf-like and unsegmented, lack hooks entirely, and have an incomplete digestive tract.
What is miracidium larva?
The miracidium is a ciliated, nonfeeding larva (Fig. 9.18). Under favorable conditions, it escapes from the eggshell, usually through the operculum, into the environment. The miracidium is elongated and covered with flattened, ciliated epidermal plates.
What are the stages of trematodes?
Not all trematodes follow the typical sequence of eggs, miracidia, sporocysts, rediae, cercariae, and adults. In some species, the redial stage is omitted, and sporocysts produce cercariae. In other species, the cercaria develops into an adult within the same host.
What is Metacercariae larva?
Definition of metacercaria : a tailless encysted late larva of a digenetic trematode that is usually the form which is infective for the definitive host.
What is Hexacanth larva?
Hexacanth is the larval stage of Taenia which are released when eggs are hatched. The hexacanth then develops into cysticercus or metacestode phase in voluntary muscles. The early cysticercus absorbs nutritive substance from host tissues and grows in size.
What is one of the main differences between Turbellarians and the trematodes and cestodes?
The Turbellarians are all free-living, and the trematodes and cestodes are 100% parasitic, with often complex life cycles.
What are the characteristics of trematodes?
Trematodes are flatworms classified in the phylum Platyhelminthes, class Trematoda, subclass Digenea. In general, trematodes are dorso-ventrally flattened and leaflike in shape. Their bodies are covered with tegument, which is usually armed with scalelike spines. They have two suckers: one oral and one ventral.
What is Glochidium larva?
: the larva of a freshwater mussel (family Unionidae) that develops as an external parasite on fish.
How do trematodes reproduce?
Inside this mollusc host the trematode undergoes asexual reproduction, producing multiple copies of a second larval form (cercaria) that either migrate into a second intermediate host (often an amphibian, fish or invertebrate) or move directly to the definitive host (normally a vertebrate).
What is polyembryony?
Ans. Polyembryony is common in citrus plants as well as mango and jamun where multiple embryos arise from sporophytic cells of ovules or zygote. 3. What is the Importance of Polyembryony?
What are the most significant trematodes?
The most significant trematodes from a clinical point of view are blood flukes, Schistosoma mansoni, S. japonicumand S. hematobium. Other trematodes of significance are intestinal fluke, Fasciolopsis buski, liver fluke, Clonorchis sinensisand lung fluke, Paragonimus westermani.
Are large rediae dominant in trematodes?
Kuris (1990) and Lafferty (1993) have generated evidence that species of trematodes with larger rediae are dominant over those with smaller rediae, or just sporocysts, and have constructed elaborate dominance hierarchies grounded on these observations.
What is the operculum of a trematode?
The trematode egg shows the operculum (arrow) characteristic of trematodes and pseudophyllidean cestodes. The ciliated trematode miracidium is the form that hatches from the egg and infects a snail as its first intermediate host.