SYSTEMATIC BIOLOGY					THE CERCOZOAE
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PHYLUM HAPLOSPORIDIA

INTRODUCTION TO THE HAPLOSPORIDIA

Haplosporidia (hap-lo-spo-RI-di-a) is made from two Greek roots that mean simple (haplos -απλός); and seed (speiro -σπείρω).  The reference is to the simple lidded spores that they produce in dispersal.

The haplosporidians are intracellular parasites of marine invertebrates.  They are united by producing a spore with a lid and a spindle that remains persistent in non dividing nuclei.  Economically, the most important species in this small phylum is Haplosporidium nelsoni, which infects oysters causing significant mortality (Figure A).  Others in the genus Urosporidium infect clams and crabs.  Some species of Urosporidium are hyperparasites and infect flukes and nematodes that parasitize crabs.  A careful survey of more than economically important marine invertebrates would likely increase the known diversity many times over.  

SYNOPTIC DESCRIPTION OF THE HAPLOSPORIDIA

SYSTEMATICS OF THE HAPLOSPORIDIA

Once considered a member of a group of protozoans called sporozoans because they were intracellular plasmodium-forming species, the haplosporidians have been taxonomic nomads.  Sprague (1982) defined the group as a separate phylum.  However, the isolation did little to advance knowledge about them.  Since then Seagrave et al. (1980), Desportes and Nashed (1983), Perkins (1990), and Siddall et al. (1995) speculated on their relationships.  Desportes and Nashed (1983) suggested an affinity with the Microsporidians, a group now allied with the Fungi.  Margulis and Schwartz (1998, PR-22) isolate the phylum at the base of their "Protochtista" tree.  Trees based on single ssu-rRNA sequence comparisons initially pointed to an affinity with the Alveolates (Siddall et al. 1995; and Flores et al. 1996).  Cavalier-Smith and Chao (2003) in an analysis of 18S-rRNA found that the the haplosporids (=Ascetosporea) were sisters to the Plasmodiophorids (=Phytomyxea).  Nikolaev et al. (2004) in a more robust analysis of ssu-rRNA and actin genes concluded that the haplosporids emerged within the foraminfera (Granuloreticulosa) clade.  I remain cautious and present them as a separate phylum within the Cercozoae.

HIERARCHICAL CLASSIFICATION OF THE HAPLOSPORIDIA

Revised: 03/14/2008