Discovery of adults of the gorgoderid trematode Cercaria duplicata with first morphological description, molecular identification and notes on host specificity.

Rhopalocercous Cercaria duplicata von Baer, 1827 develops in an intermediate host, the unionid bivalve Anodonta anatina (L.), but its adult form has been unknown. We examined eight fish species occurring in the presence of a highly infested population of A. anatina in the Zeslawice reservoir (S Poland). Gravid Phyllodistomum specimens were obtained from the ureters of ide, Leuciscus idus (L.) and common rudd, Scardinius erythrophthalmus (L.). One of the rudd specimens was doubly infected, a trematode was also found in the urinary bladder. In addition, a gravid Phyllodistomum specimen was found in the ureter of a tench Tinca tinca (L.), caught in Lake Ilmedas (Lithuania). In order to clarify the phylogenetic position of larval and adult gorgoderids and to establish their life cycle, ITS2 and 28S rDNA sequences were analysed. The analysis showed that adult Phyllodistomum specimens located in the ureters are conspecific with C. duplicata. The trematode found in the urinary bladder of S. erythrophthalmus was P. folium (Olfers, 1816). It is suggested that adult stages of C. duplicata should be referred to as Phyllodistomum duplicatum n. comb. The intercaecal position of the uterus and the deeply-lobed ovary are the main features distinguishing it from other Phyllodistomum species. Host specificity and ecology are discussed.

The size and shape of parasitic larvae of naiads (Unionidae) are not dependent on female size.

The naiads, large freshwater mussels (Unionida), have very long life spans, are large-bodied, and produce thousands to millions of larvae (glochidia) which typically must attach to host fish tissues to metamorphose into a juvenile mussel. Glochidia develop within a female's marsupial gill demibranch, thus their number is restricted by female size. However, larger mussels acquire more energy, which could be invested in either larger-sized glochidia, in a more glochidia, or a combination of both. The high level of host specialization seen in many naiads may constrain glochidial size and shape around a narrow optimum, while naiads that use a wide range of host fishes may be predicted to possess greater plasticity in glochidial morphology. In this paper, we investigated the relationship between maternal body size and progeny body size and shape, aided by modern digital microscopy. We analyzed the between- and within- species variation of glochidia size and shape relative to female size in four widespread species of European naiads: Anodonta anatina, Anodonta cygnea, Unio crassus and Unio tumidus. Whereas the total reproductive output is collinear with female body size, substantial differences between species in glochidia size were found within genus Anodonta, but not genus Unio where glochidial size is remarkably consistent. The glochidial shape, however, differed within both Unio and Anodonta. We interpret this constant within-species glochidial size in Unio as reflecting a constraint imposed by the likelihood of successful transmission onto and off from a narrow range of hosts, whereas their shape seems to be less constrained. The Anodonta species, inhabiting a wide spectrum of habitats and using more than twice the number of fish hosts than Unio spp., have larger glochidia with greater variation in size and shape. Our results suggest that measures of glochidial variability may also serve as an indicator of host specificity in other naiads.