The life-cycle of nasitrematids (or that of the related campulids) is not
known, but it is likely to take a typical digenean sequence. Where the
metacercaria exists is a conundrum.
If you contact me directly and specify your requirements, then I can provide
the available references on the genus Nasitrema.
Dr David I. Gibson
Parasitic Worms Division Tel. +44-(0)171-938-9485
Department of Zoology Fax. +44-(0)171-938-8754
The Natural History Museum
London SW7 5BD
Work e-mail: dig at nhm.ac.uk
Home e-mail: p-d.gibson at dial.pipex.com