Mantle-shell complex reactions elicited by digenean metacercariae in Gaimardia trapesina (Lamarck, 1819) (Bivalvia: Gaimardiidae) from the Magellan Strait.

CRISTIÁN, ITUARTE; FLORENCIA CREMONTE; GUILLERMO DEFERRARI

DISEASES OF AQUATIC ORGANISMS

INTER-RESEARCH

Año: 2001 vol. 48 p. 47 - 56

0177-5103

The host response to three different larval digeneans affecting Southwestern Atlantic and Magellanic populations of the bivalve Gaimardia trapesina (Lamarck, 1819) (Gaimardiidae) is described. Unencysted metacercariae of 2 species of Gymnophallidae and 1 species of Lepocreadiidae co-exist in the peripheral and general extrapallial spaces. Differences in host responses to stimuli generated by each parasite are described. Infections by Gymnophallidae gen. sp. 1 metacercariae elicit a mantle-shell complex reaction involving both alteration of the mantle epithelium (hyperplasia and metaplasia) and calcium carbonate deposition to form an incomplete calcareous covering of single larvae, comprising individual crystallites in an organic matrix. The calcareous covering covers only the posterior two thirds of the larval body, having its anterior end free in the extrapallial space, which secures the survival of the larvae. The peculiar features of the host response are viewed as the result of a successful process of adjustment to the parasite´s life cycle. Metacercariae of Gymnophallidae gen. sp. 2 occur in one or more small groups of up to 30 individuals, either in the general or in the peripheral extrapallial spaces. The outer mantle reaction includes hyperplasia and metaplasia of the epithelium adjacent to the larvae. Deposition of calcium carbonate did not occur. Lepocreadiidae gen. sp. metacercariae were observed exclusively in the general extrapallial space lodged in single shallow pits whose shape fit the parasite´s body shape and size. In simultaneous infections, metacercariae of Gymnophallidae and Lepocreadiidae elicited different responses in an individual, which suggests that each parasitic entity involves a different stimulus to the host.