Tissue reaction of Tagelus plebeius Lightfoot (Bivalvia, Psammobiidae) against larval digeneans in mixohaline habitats connected to the Southwestern Atlantic Ocean

ITUARTE, CRISTIÁN F; CREMONTE, FLORENCIA; SCARANO, AGOSTINA

JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM

CAMBRIDGE UNIV PRESS

Año: 2009 vol. 89 p. 569 - 577

0025-3154

Abstract. The studied population of the stout razor clam Tagelus plebeius from the Mar Chiquita mixohaline lagoon (37º 32’S, 57º 19’W) showed a 100% of prevalence of infection by a larval digenean (metacercariae) of the family Gymnophallidae. The larvae occupied the extrapallial space just below the hinge of the bivalve. The structure of the tissular reaction against larval digeneans in Tagelus plebeius consisted in the hyperplasia and metaplasia of the outer layer of the mantle epithelium adjacent to parasites, forming an invagination to generate a sac that surrounds larvae. According to the intensity of infection, each sac progressively enlarges, lodging a variable number of larvae. In highly infected clams, a great number of sacs are formed. Eventually, the older sacs containing larvae may become closed, loosing their communication with the extrapallial space and sinking into the dorsal part of the visceral mass.  Larvae within sacs grow and remain alive until reach an appropriate definitive vertebrate host.  In old infections it is common to observe remains of dead larvae which have undergo resorption; as a result, a yellowish or brownish amorphous material accumulates into the space once occupied by the larvae; in some cases, calcifications in the form of pearls or blisters were observed.