An Analysis of the Methods used in the Study of Larval Trematodes

Let's restart formally naming 'larval' trematodes

Arguably the most unique biological features of trematode parasites involve their clonal parthenitae and cercariae. These life stages are biologically fascinating, medically and scientifically important, and often studied for years, lacking knowledge of their corresponding sexual adult stages. But sexual adults are the focus of trematode species-level taxonomy, partially explaining the relative neglect of documenting the diversity of parthenitae and cercariae and why researchers who do describe them give them only provisional names. Provisional names are unregulated, unstable, often ambiguous, and, I argue, often unnecessary. I suggest that we recommence formally naming parthenitae and cercariae using an improved naming scheme. The scheme should permit us to reap the benefits of formal nomenclature and thereby enhance research involving these diverse and important parasites.

The life cycle of Stegodexamene anguillae n.g., n.sp., an allocreadiid trematode from New Zealand

1. A new genus of trematode (family Allocre-adiidae) from the intestine of freshwater eels is described, and named Stegodexamene anguillae.

2. The genus is related to Aephnidiogenes, Lepidapedon and Neophasis, but differs significantly from each of them.

3. The life cycle followed is from the adult in Anguilla dieffenbachii to the redia in Potamopyrgus antipodum (fresh-water gastropod). The cercaria encysts in the eloetrid fish Gobiomorphus gobioides.

4. Progenetic production of eggs and spermatozoa occurs in the metacercariae.

5. Metacercarial excretory spherules are composed of calcium carbonate.

Life cycle of Coitocaecum anaspidis Hickman, a New Zealand digenetic trematode

The life cycle of Coitocaecum anaspidis involves three important stages. The adult occurs in Galaxias brevipennis, G. attentuatus, Gobiomorphus gobioides, and in specimens of Anguilla spp. less than 30 cm. long. Potamopyrgus antipodum and P. badia are the molluscan hosts of the sporocyst and cercaria. In New Zealand the cercaria attacks and encysts in Paracalliope fluviatilis, and in Australia in Anaspides tasmaniae. A metamorphosis of the cercarial larva into a progenetic metacercaria takes place in the amphipod.

Paracalliope does not become infected with Coitocaecum till the crustacean has reached 2·0 mm. in length. The thigmotropism of the Paracalliope fits exactly with the ground-living habit of the stumpy-tailed cercaria. The small river fish feeding in slack water acquire Coitocaecum from Paracalliope.

Some Larval Trematodes from the Coast in the Region of Roscoff, Finistère

Seven species of cercariae and four of metacercariae collected at Roscoff, Finistère, during August, 1931, are described. They have been referred to appropriate systematic groups and wherever possible, probabilities concerning life histories are suggested. Four of the cercariae and two of the metacercariae are recorded as new to science.

The Trematode Parasites of Turritella communis Lmk. from Plymouth and Naples

In 1931 Dr M. V. Lebour drew my attention to a larval Trematode (one of the “Hugetailed Monostome” group of H. M. Miller, 1925) which occurred quite frequently in Turritella communis from the Rame Mud, Plymouth. During 1932–4 I examined 541 Turritella communis from the same locality and an 8 per cent. general infection with four species of closely related cercariae was recorded, but the species which was common the previous year did not occur once. 180 Turritella communis from Naples revealed a 5 per cent, infection of two other closely related species.

Use of acetic orcein as a fast method to relax, fix, clear and stain cercariae for light microscopy

Acetic orcein stain may be dropped onto the specimen before applying a cover slip. This single reagent reveals cercarial and metacercarial structures that would otherwise be made visible only by complicated and time consuming procedures.