Larval trematodes infecting the South-American intertidal mud snail Heleobia australis (Rissooidea: Cochliopidae)

Abstract

Larval trematodes infecting the snail Heleobia australis (Cochliopidae) from the Bahía Blanca estuary, Argentina were surveyed for two years. A total of 7,504 snail specimens was dissected and the larval stages of 15 different trematodes were recovered and examined morphologically. These larvae included four species that had previously been reported from H. australis in Brazil, Uruguay, and Argentina: the heterophyid Ascocotyle (Phagicola) longa and the microphallids, Maritrema bonaerense, Maritrema orensense, and Microphallus simillimus. Three other species, the echinostomatid Stephanoprora uruguayensis, the microphallid Levinseniella cruzi, and the psilostomid Psilochasmus oxyurus are reported here for the first time as parasites of H. australis. Eight other trematodes found in H. australis are described and placed in the appropriate superfamilies, families or genera (Cryptogonimidae, Apocreadiidae, Aporocotylidae, Notocotylidae, Haploporidae, Renicolidae, Himasthla, and Renicola). The prevalence of the trematode taxa infecting H. australis in the Bahía Blanca estuary was low (<3%) with a single exception (M. simillimus; >20%). Microphallidae were the richest and the most prevalent family, probably because of the high abundance of crabs -the second-intermediate hosts of certain microphallid species -and the considerable diversity of gulls. Here we compare the parasite assemblage found in the H. australis from Bahía Blanca estuary with other parasite assemblages infecting Heleobia spp. and other rissooids from the rest of the world.

A checklist of marine larval trematodes (Digenea) in molluscs from Argentina, Southwestern Atlantic coast

“…From 46 larval trematodes species recorded in 25 molluscan species in Brazil, only five are marine. The records of larval trematodes from freshwater molluscs (at least 95 species) from Argentina are much higher (e.g., Ostrowski de Núñez 1992; Ostrowski de Núñez et al 1997;Flores and Semenas 2008;Martorelli et al 2013;Alda and Martorelli 2014), than Chile and Brazil. However, the number of records from marine molluscs is higher than Chile and Brazil (31 digenean species from 20 molluscs).…”

A strong colonizer rules the trematode guild in an intertidal snail host

“…Once M . simillimus has colonized the snail's tissue, parthenogenetic generations produce metacercariae that occupy the entire gonad and most of digestive gland of the host (Alda and Martorelli ). These metacercariae are most likely invulnerable to the attack by rediae and thus potentially resistant to removal by (co)dominant species, which could explain the high prevalence of M .…”

“…, Lie , , Lim and Heyneman , Combes ): (1) rediae species dominate sporocyst species (redia have a muscular pharynx used to consume host tissue and also attack and feed on other invading trematodes), (2) rediae species with large pharynges dominate rediae species with small pharynges. We also analyzed the snail‐tissue occupancy area of dominant and subordinate trematodes using longitudinal histological sections of uninfected and infected tissue of the intertidal snail Heleobia australis that were previously obtained by Alda and Martorelli (). Next, we accounted for the expected prevalence of each species ( e ) for each model.…”

“…The overall infection prevalence in this host population is 28% but a seemingly subordinate species, Microphallus simillimus (Microphallidae), makes up 86% of the infections, with the rest of the species presumably (co)dominant to M . simillimus being less than 1% of the infections (Alda and Martorelli ). As a result, with a first to second species ratio of 30, this community is far more skewed than any parasite community studied (e.g., Poulin et al.…”

“…Heleobia australis has a wide geographic range (from Brazil, 22°54 0 S, to Argentina, 40°84 0 S; De Francesco and Isla 2003) and is common in the estuaries and coastal lagoons where it hosts 18 larval trematode species. Alda and Martorelli (2014) reported 15 of these from the Bah ıa Blanca estuary (Argentina), and found that all but one are parasitic castrators, with an individual worm eventually filling up the digestive gland and gonad of the snail host (increasing the potential for competition). The overall infection prevalence in this host population is 28% but a seemingly subordinate species, Microphallus simillimus (Microphallidae), makes up 86% of the infections, with the rest of the species presumably (co)dominant to M. simillimus being less than 1% of the infections (Alda and Martorelli 2014).…”