As mesokaryotic cells contain a well-organised nucleus like that of eukaryotic cells, but its nucleus divides through amitosis like that of prokaryotes, so the cells are termedmesokaryotes which indicates its nucleus resembles both eukaryotic and prokaryotic nucleus.

Dinoflagellate is mesoaryotic but according to ncert u will refer it to be eukaryotic

Mesokaryotes are intermediates between prokaryotes and eukaryotes.

dinoflagellates are eukaryotic according to NCERT class11 BIOLOGY

IN GENERAL THEY ARE CONSIDERED 

In general they are considered EUKARYOTIC