A DESCRIPTION OF HAPLOZOON AXIOTHELLAE N. SP., AN ENDOSYMBIONT OF THE POLYCHAETE AXIOTHELLA RUBROCINCTA¹²

Abstract

SUMMARY A new parasitic dinoflagellate, Haplozoon axiothellae sp. nov., is described from the intestine of the marine polychaete Axiothella rubrocincta. The parasites are 40–175 μm long with 2–26 cells arranged in single or double rows. Two cytoplasmic inclusions previously unknown in this genus are described. The first is globular and varies in size, while the second is approximately 2 μm long and peanut‐shaped. The function and composition of the inclusions are unknown. Nuclear structure and karyokinesis are apparently different from those of typical dinoflagellates.

CHARACTER EVOLUTION IN POLYKRIKOID DINOFLAGELLATES1

“…The pseudocolonial cell organization of Polykrikos species is among the most novel features of these dinoflagellates. A similar cellular organization has also been described for parasitic dinoflagellates, such as Haplozoon Dogiel, where, for example, H. axiothellae Siebert forms a compartmentalized syncytium (Siebert 1973, Siebert and West 1974, Leander et al 2002). The compartments in the pseudocolonies of H. axiothellae each contain at least one nucleus, are partitioned by alveolar membranes, and are enveloped by a continuous plasma membrane.…”

Surface morphology of the marine parasite Haplozoon axiothellae Siebert (Dinoflagellata)

“…The posteriormost surface of each trophocyte was distinctly smooth and identified as the "neck", where the dorsal region of the neck was much broader (7-11 µm at maximum breadth) than the ventral region (Figs 1, 2a-c). We infer that the neck region contains the nucleus of the trophocyte as TEM data demonstrated that the nucleus is located in the posterior third of each trophocyte (Siebert 1973;Siebert and West 1974).…”

“…Accordingly, we have examined the surface morphology of thirteen different individuals of H. axiothellae using scanning electron microscopy (SEM) to complement the two original papers describing H. axiothellae with TEM (Siebert 1973;Siebert and West 1974). We not only report new findings on the structures noted above, but we provide evidence for what we suspect are unusual episymbionts and evidence which indicates that each individual parasite is surrounded by a single membrane.…”

“…The light microscopical observations of Chatton (1919) led to predictions that hap-pyramid), pictinate (cells arranged in one plane as a triangular sheet), and linear (cells arranged as a single longitudinal row) (Chatton 1919;Shumway 1924). The remaining species, Haplozoon axiothellae Siebert, was collected from the eastern Pacific Ocean and described with light and transmission electron microscopy as a linear form that occasionally produced a double row of cells near the posterior end (Siebert 1973;Siebert and West 1974). These observations suggested that H. axiothellae had a number of surface features that were impossible to adequately characterize with TEM, such as patterns of thecal plates, the distribution of thecal barbs, surface details of the attachment apparatus, and patterns of thecal pores.…”

Parasitic Life Styles of Marine Dinoflagellates1

“…For example, Myxodinium pipiens is presumably restricted to the chlorophyte genus Halosphaera, yet this parasite is only known from one study of Mediterranean plankton. Similarly, the 10 species of Haplozoon most of which have been reported only once, are believed to be highly host specific, with each infecting a single host species (Shumway 1924;Siebert 1973).…”