Search

The adult fluke Stomylotrema vicarium (Stomylotrematidae, Microphalloidea) was described for the first time in Theristicus caerulescens in 1901, but the complete life cycle has remained unknown to date. Here, we found a stomylotrematid trematode in the digestive gland of the endemic apple snail Pomacea americanista. The digestive gland's tubuloacini were compressed by the trematode larvae placed on connective tissues and haemocoel spaces. Non-virgulate, stylet-bearing cercariae showed three pairs of penetration glands with a body, oral sucker and stylet morphometrically similar to those of stylet-bearing, unencysted young metacercariae of S. vicarium found in the aquatic coleopteran Megadytes glaucus, and at a lesser extent with cercariae of S. gratiosus found in the apple snail Pomacea maculata. The larvae molecular phylogeny was inferred using the markers rRNA 28S and ITS1, being these sequences grouped with the sequences of S. vicarium obtained from adult flukes. Together, these findings indicate that the life cycle of S. vicarium begins in P. americanista, thus supporting the hypothesis that the ampullariid snails act as a first intermediate host. [ABSTRACT FROM AUTHOR]

The sacoglossan Plakobranchus ocellatus feeds by sucking the cytoplasmic contents from algae and retains intact algal chloroplasts within the cells of the digestive gland. Morphology of the entire digestive system of this species was firstly described by means of a combination of histology and electron microscopy (both SEM and TEM). The short alimentary canal is confined to the head, and the anus opens at the anterior right corner of the pericardial swelling, as is the case in many non-shelled sacoglossans. The alimentary canal of the specimens examined rarely contained ingesta, suggesting that the retained chloroplasts provide sufficient nourishment to the sacoglossan hosts and that sea slugs with empty stomachs survive well in the field. The digestive gland, with the retained chloroplasts, branches from the stomach and is sparsely distributed throughout the body, including the head region, but is aggregated mainly in the dorsal lamellae. Chloroplasts were occasionally found in the epithelial cells in the transitional region from the stomach wall to the digestive gland, which may be a site at which chloroplasts are incorporated into the animal cells by endocytosis. Numerous microvilli filling the lumen of the digestive gland suggest that molecules are actively transferred within the gland. The sea slug thus apparently provides a favorable environment to support the long-term retention and function of chloroplasts. [ABSTRACT FROM AUTHOR]

Since January 1993, neurological symptoms and rapid deaths (5 to 10 min) were typically observed in the mouse bioassay of acetone extracts of digestive glands from Arcachon and Toulon (France) during the winter season. It was assumed initially that a new lipophilic toxin waspresent because tests using the AOAC mouse bioassay for paralytic shellfish toxins on acid extracts of whole shellfish meat were negative, no known lipophilic toxins were detected and no toxic phytoplanktonspecies were observed in the area during the poisoning events. In this study, however, preparative isolation of the toxic factor from toxic mussel digestive glands has revealed the presence of paralytic shellfish toxins, the principal ones being gonyautoxins-2 and -3 at Arcachon and gonyautoxins-1, -4, -2 and -3 at Toulon. The toxin concentrations recorded were below levels harmful to consumers and therefore represent a false positive in the mouse bioassay for lipophilic toxinsbased upon acetone extraction. The origin of the toxins remains to be determined. [ABSTRACT FROM AUTHOR]