[| 57 J 
Meduse as Hosts for Larval Trematodes. 
By 
Marie V. Lebour, M.Sc., 
Assistant Lecturer in Zoology, Leeds University. 
Temporary Naturalist in the Plymouth Laboratory. 
With Figure 1 in the Text. 
Tue larval form (late cercaria stage) of Pharyngora bacillaris (Molin) has 
been recorded by Nicoll (1910) from Plymouth as occurring free in the 
coarse-meshed tow-nettings in August. The adult is a common parasite 
of the mackerel, and the above is the only record of its larval stage. 
Whilst examining tow-nettings at Plymouth in 1915 it was found 
that certain medusz were at times abundantly infected with a trematode 
which proved to be the larval form of Pharyngora bacillaris. As it also 
occurred free, although almost certainly having originally come from 
the medusz, it is obviously the form recorded by Nicoll, who expected 
the host to be a crustacean and unsuccessfully examined copepods in 
order to find it. 
The medusz found to contain the trematode were Obelia sp., Cosmetira 
pilosella, and Turris pileata. Cosmetira pilosella was the commonest host 
in the early summer when Pharyngora was most abundant, but in the 
later summer Obelia was found to contain it frequently, Cosmetira not 
occurring at those times in the tow-nettings. Phialidium hemisphericum 
was also a host in the later summer and autumn. Even in December it 
still occurred, though very rarely. A ctenophore may also serve as host 
for this trematode, as it is occasionally found clinging to the inside of the 
stomach of Pleurobrachia pileus. 
The parasite is generally to be found clinging to the manubrium or 
stomach wall of its host, but sometimes it occurs underneath the umbrella 
wall, so that it looks as if it were on the top, the wall being so transparent ; 
on further examination, however, it is seen to be underneath. It seems 
to be undoubtedly a case of parasitism as so many of the medusz were 
infected, sometimes every specimen in a haul, and, with the exception of 
an occasional ctenophore, none of the other animals in the same haul 
contained them or had them clinging to them. 
