tree constructed using this data (Fig. 6) revealed that the sequence
of the microsporidian from P. monodon most closely grouped with
N. salmonis and E. bieneusi.
4. Discussion
This is the first report on ultrastructural features and a partial
SSU rRNA gene sequence of a microsporidian exclusively infecting
hepatopancreatic tubule epithelial cells of the black tiger shrimp P.
monodon. Its unique ultrastructural features linked it to the family
Enterocytozoonidae. Based on its distinction from the microsporidian
genera Nucleospora and Enterospora in the family and on its
similarity to the single species in the genus Enterocytozoon, we assigned
the new microsporidian infecting P. monodon to the genus
Enterocytozoon. We believe that its occurrence in an invertebrate
host and its relatively low SSU rRNA sequence identity with E. bieneusi
justify its assignment to a new species within the genus.
The name E. hepatopenaei is proposed for the new species with
justification based on ultrastructural characters that conform to
the unique features of the family Enterocytozoonidae but distinguish
it from other species in the family, i.e., E. beiniusi that also
develops in the host-cell cytoplasm and species in the genera Ent-