User:KyleMadden24/Trematode Miracidium Draft

Trematode Miracidium

The miracidium is the second stage in the life cycle of the trematodes (Trematode life cycle stages). Upon hatching from their eggs the trematodes enter the Miracidium phase of their life cycle.

References

The species of trematode Hirundinella ventricosa is found to release eggs in strings. Each egg was found to contain a single miracidia and the string was they were attached to contained living spermatozoa. When taken from the eggs and examined the miracidia were found to have cilia were only present in the upper portion of the body near an apical gland with 12 hook like spines present in the opening. The way in which the eggs were opened to observe the miracidia is to be considered unnatural as under normal circumstances they would have hatched in the body of a host organism.

Trematodes initial larval stage is the miracidium. Miracidia usually require entering a mollusk host before they can start growing and begin asexual reproduction. Both light and scanning microscopy was used for studying the miracidia. N. squamipes a type of aquatic rodent which has been found to be a main host for adult E. paraensei where captured, infected with the trematodes and were then euthanized to extract and examine the trematode eggs inside them. They used specific light and heat conditions to get the eggs to hatch and then the live miracidia were placed on slides to be observed by light and video microscopy. The miracidia were observed to have 18 plates along the outside of their body. The sizes of the miracidia did not appear to be affected much by the different types of rodents they had been allowed to produce in past experiments.

The ability and efficiency of the miracidia finding a host is a crucial factor in the growth and success of later life stages. Schistosome miracidia have been found to have a three phase process they go through when searching for a host. In phase one the miracidia use light gravity stimuli to concentrate in areas that are likely the most attractive to the snail hosts they are searching for. The second phase consists of just moving around at random in the area in search of a host. Phase three Is when the miracidia finally finds a host and begins honing in on it and preparing to penetrate into the host. It is assumed that other species of miracidia follow the same three phase pattern. Chemosensitivity plays a large role in how the miracidia find a host, but it is not specific enough for the parasite to specific host species that are vulnerable to infection opposed to other snail species which are not susceptible to infection and can not be properly reproduced within.

There are carbohydrates along the surface of the of the miracidia of trematodes that interact with the lectins produced by the gastropods. The organization and number of these carbohydrates shift as the miracidia begin to enter the change in lifecycle stage to the next step in their development the sporocyst (Trematode life cycle stages). Certain carbohydrates are bound all over the body of the sporocyst stage but have only been found to be present on the "intercellular ridges" of the miracidia.

The miracida were able to be viewed both inside and outside of the eggs using light microscopy and silver nitrate. Even when about to hatch the eggs showed no signs of specializations such as projections or spine like structures. By adding slight pressure they were also able to observe the exact moment in which the miracidia hatched from their eggs and reported them as having elongated bodies "with one interepidermal ridge in the anterior row". They also observed one "interepidermal ridge" and once outside the egg they could even see a singular "exretory vesicle" which allowed them to interoperate the front and back of each miricidia. They were described as being "peach shaped" overall and the body is covered in cilia.

The miracidia in this experiment were oval shaped and their body was covered in cilia almost entirely except for the most anterior portions which are taken up by "apical papilla". Each miracidium has four papilla on each of their sides which contain sensorial hairs. They each have an apical gland that leads to the apical papilla. They have four rows of epidermal plates organized into four rows with row two being made up of 8 plates while the other three rows each have six. They were able to observe eye spots on the miracidia which were dark brown in pigmentation and in a shape similar to an inverted capital letter L and were located between the first and second row of plates on the body. A singular "large cephalic ganglion" along with a number of smaller nuclei are what make up the nervous system of the miracidia.