Molecular phylogeny and ultrastructure of two novel parasitic dinoflagellates,Haplozoon gracile sp. nov. and H. pugnus sp. nov

This study describes two novel parasitic dinoflagellates:Haplozoon gracile sp. nov. isolated from a bamboo worm (Maldanidae), 'cf.Petaloclymenesp.'sensuKobayashiet al. 2018; and,H. pugnus sp. nov. isolated fromNicomachesp. andNicomache personata(Maldanidae). Trophonts (feeding stages) were observed with light, scanning, and transmission electron microscopy. Molecular phylogenetic analyses were performed based on 18S rDNA. COI sequences were obtained for host organisms. Trophonts ofH. gracilewere linear (single longitudinal row) and relatively slender with a mean length of 190 mu m, and consisted of a long and narrow trophocyte, rectangular gonocytes (mean width = 10 mu m), and slightly rounded sporocytes. Trophonts ofH. pugnuswere pectinate (1-8 rows of sporocytes in one plane), with a mean length of 179 mu m, consisting of a bulbous trophocyte, rectangular gonocytes (mean width = 25 mu m), and rounded sporocytes. The body of both species was covered with many depressions that overlaid the amphiesmal vesicles. TEM observations of trophocytes inH. gracilerevealed a stylet with a central dense core and rich mitochondria subtending the amphiesma. Furthermore, amphiesmal vesicles appeared to contain thecal plates in both species. Phylogenetic analyses generally resolved aHaplozoonclade, andH. gracileandH. pugnuswere clearly distinguished from other species for which molecular data are available. Based on the morphological and host comparisons with all described species and their molecular phylogeny, we conclude that these two isolates are new species ofHaplozoon, H. gracile sp. nov. andH. pugnus sp. nov.