Research Article

‘Total evidence’ refutes the inclusion of Perkinsus species in the phylum Apicomplexa

M. E. SIDDALL a1 , K. S. REECE a1 , J. E. GRAVES a1 and E. M. BURRESON a1
a1 Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA


The phylogenetic affinities of the oyster pathogen Perkinsus marinus were investigated with morphology, 18S-like rDNA data and actin sequence data. Morphological investigations revealed that Perkinsus species do not have a conoid and that other criteria which have been used to place them in the Apicomplexa are general to alveolates. When considered separately, 18S-like rDNA and actin data sets each support a closer affinity for Perkinsus marinus with the dinoflagellates. However, each of these separate analyses possess their own biases and weaknesses. Use of the phylogenetic principle of ‘total evidence’ in which data sets are combined in simultaneous analysis yielded a more robust hypothesis that is stable both to character and taxonomic sampling. The resulting cladogram strongly corroborates the placement of Perkinsus species with the Dinoflagellida and not with the Apicomplexa.

(Received August 28 1996)
(Revised January 20 1997)
(Accepted January 20 1997)

Key Words: congruence; Dinoflagellida; Perkinsus; phylogeny; Apicomplexa.


Corresponding author. Present address: Museum of Zoology, University of Michigan, Ann Arbor, MI 48109, USA. Fax: 001 804 642 7399. E-mail: