Penilia avirostris has been reported to feed efficiently
on prey such as heterotrophic microflagellates,
small diatoms and autotrophic flagellates (Turner et al.,
1988). Small diatoms such as Skeletonema costatum,
which is the dominant diatomduring spring in the Gulf
of Trieste, were found in the guts of P. avirostris when
analyzed with SEM by Kim et al. (1989). They also
found a lot of unidentifiable small particles, probably
flagellate remains. In our study, we found no diatoms
in the guts of P. avirostris observed under the epifluorescence
microscope.