DESCRIPTION OF THE KINGDOM HACROBIAE (CAVALIER-SMITH 2010)

EUKARYA> CHROMALVEOLATA> HACROBIAE

Hacrobiae (ha-KRO-bee-ee) was coined by Cavalier-Smith (2010) by taking the first two letters of the dominant taxa: HA (from Haptomonada) and CR (from Cryptomonada). The suffix comes from one of the Greek words for living or life: BIOS (βίος).

INTRODUCTION TO THE HACROBIAE Members of this kingdom are eukaryotic protists with flattened or tubular cristae. Presently, the kingdom is made up of three phyla: the cryptomonads, the haptophytes, and the centrohelids. These groups seem to be sisters and form a loose clade that is a sister to the heterokonts (stramenopiles) +alveolates (Baldauf 2003a). In her synthesis, though, Baldauf (2003a) has the cryptomonads and haptomonads associated with the base of the typical heterokont – alveolate line in a sister group relationship. Harper et al. (2005) use a 6-protein phylogeny of eukaryote taxa and provide further evidence of the cryptomonad+haptomonad clade and its sister relationship with the alveolates+heterokonts. Keeling (2004) also suggests the same relationship in a supergroup called the chromalveolates [formalized to Chromalveolata]. On the other hand, Cavalier-Smith and Chao (2003c) and Nikolaev et al. (2004) suggest that the haptophytes are sisters to the stramenopiles+rhizaria+alveolata while the cryptophytes are sisters to the plants. Hackett et al. (2007) provide convincing evidence that the Chromalveolata+Rhizaria are sisters to the Haptophytes + Cryptophytes. The centrohelid heliozoans emerge erratically as sisters of the cryptomonads (Nikolaev et al. 2004); and of the haptomonads (Cavalier-Smith 2003a); so, as a convenience, we have placed them in this kingdom. Analyses of Burki et al. (2009) and Okamoto et al. (2009) confirm that the existence of a monophyletic taxon (named Hacrobia by Cavalier-Smith 2010b) that includes centrohelids cryptophytes and haptophytes. The relationship of the Hacrobia with the other chromalveolates, however, needs more work.

FURTHER READING: DISCOVERY OF THE DOMAINS OF LIFE INTRODUCTION TO THE DOMAIN EUKARYA

LITERATURE CITED Baldauf, S. L. 2003a. The deep roots of eukaryotes. Science. 300 (5626): 1701-1703. Cavalier-Smith, T. 2003a. Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology. 39:338-348. Cavalier-Smith, T. and E. E. Chao. 2003c. Molecular phylogeny of centrohelid heliozoan, a novel lineage of bikont eukaryotes that arose by ciliary loss. Journal of Molecular Evolution. 56:387-396. Cavalier-Smith, T. 2010b. Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree. Biology Letters. 6: 342-345. Hackett, J. D., H. S. Yoon, S. Li, A. Reyes-Prieto, S. E. Rummele, and D. Bhattacharya. 2007. Phylogenomic analysis supports the monoplyly of Cryptophytes and Haptophytes and the association of Rhizaria with Chromalveolates. Molecular Biology and Evolution. 24(8): 1702-1713. Harper, J. T., E. Waanders, and P.J. Keeling. 2005. On the monophyly of chromalveolates using a six-protein phylogeny of eukaryotes. International Journal of Systematic and Evolutionary Microbiology. 55: 487-496. Keeling P. J. 2004 The diversity and evolutionary history of plastids and their hosts. American Journal of Botany. 91(10): 1481-1493. Kühn, A. 1926. Morphologie der Tiere in Bildern. 2 H. In: Protozoen. Berlin. pp.107-272. Margulis, L. and K. Schwartz. 1998. Five Kingdoms, An Illustrated Guide to the Phyla of Life on Earth. W. H. Freeman and Co. New York. Nikolaev, S. I., C. Berney, J. Fahrni, I. Bolivar, S. Polet, A. P. Mylnikov, V. V. Aleshin, N. B. Petrov, and J. Pawlowski. 2004. The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes. Proceedings of the National Academy of Sciences. USA. 101(21): 8066-8071. Okamoto, N., C. Chantangsi, A. Horak, B. S. Leander, and P. J. Keeling. 2009. Molecular phylogeny and description of the novel katablepharid Roombia truncata gen. et sp. nov., and establishment of the Hacrobia taxon nov. PLoS One 4(9):e7080.

By Jack R. Holt. Last revised: 02/23/2014