Biomphalaria pfeifferi, (Krauss, 1848) (Krauss, 1848)

Ataev, Gennady L., 2023, ЭкспериментаΛьное изучение вΛияния метацеркарий Echinostoma caproni на выживаемость моΛΛюсков Biomphalaria pfeifferi, Amurian Zoological Journal XV (4), pp. 712-723 : 714

Exposure of B. pfeifferi to metacercariae

E. caproni cercariae rarely penetrate B. pfeifferi through their external shells. Instead, they mostly infect the snails through the epithelial tissue of their mantle collars. Generally, cercariae penetrate snails directly from their mantle cavity, which they infiltrate through the pneumostome. They can also penetrate the dorsal part of a snail through the epithelial tissue, but most of the time they move from the mantle cavity to the kidney via the excretory pore. Some cercariae start encysting here, but most of them migrate into the pericardial cavity through the renopericardial canal. This is where the majority of metacercariae localize.

Before penetrating a snail host, cercariae tend todiscardtheirtailsandmovebyrapidlycontracting their bodies ( Fig. 1 : C). We have encountered only one case of a cercariae retaining its tail even after penetration. ( Ataev 2010). During the encystment, the body of a cercariae twists on its ventral side and then quickly gets covered with a three-layer cyst wall formed by the secretion of cystogenous glands. The entire encystment process takes no more than 4 hours.

Afterwards, metacercariae get encapsulated in hemocyte capsules ( Fig. 1 : D). Hemocyte also creates a fibrous tissue, which makes separate cysts stick together into large conglomerations. Metacercariae have a spherical form with a diameter of 155 ± 1.9 mcm (n = 100). At first, the outer wall of metacercariae is transparent, but turns opaque after a week. These metacercariae are infective and stay that way for more than a month. Larvae start dying 50 days after. Their size shrinks by half and the surface of their capsule gets loose. Thus, our results did not confirm the findings of N. O. Christensen et al. (1980) who determined the lifespan of metacercariae as 4 months.

Figures

Fig. 1. Stages of development of an Echinostoma caproni trematode (A–D): A — SEM microphotograph of a motherredia;B —histological section of a cercariaembryo in adaughter redia; C — SEM micrograph of a cercaria with a discarded tail; D — SEM micrograph of a metacercaria. Legend: bp — birth pore, h — hemocytes, m — mouth, os — oral sucker, t — tail, vs — ventral sucker Рис.1. СтаΔии развития трематоΔ Echinostoma caproni (A–D): A—SEM-микрофотография материнской реΔии; B — гистоΛогический срез эмбриона церкарии в Δочерней реΔии; C — SEM-микрофотография церкарии с отброшенным хвостом; D — SEM-микрофотография метацеркарии. УсΛовные обозначения: bp — роΔиΛьная пора; h — гемоциты; m — ротовое отверстие; os — ротовая присоска; t — хвост; vs — брюшная присоска