DESCRIPTION OF THE PHYLUM CYCLIOPHORA (FUNCH AND KRISTENSEN 1995)

EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> BILATERIA> PROTOSTOMATA> SPIRALIA> TROCHOZOA> POLYZOA> CYCLIOPHORA

Cycliophora (si-kle-O-fo-ra) is derived from two Greek roots that mean wheel bearers [wheel- kyklos (κύκλος); and bearer -phoro (φέρω)]. The name refers to the apparent “turning” of the ciliary ring around the mouth.

INTRODUCTION TO THE CYCLIOPHORA The cycliophorans were found recently by Funch and Kristensen (1995) attached to the mouthparts of lobsters in the North Atlantic. Since then, they have been found on other decapod crustaceans. They are filter feeders like entoprocts, to which they appear to be related (Figure 1). Cycliophorans are sedentary animals and presumably feed from the leavings of the decapod crustacean host. The small and simple animal almost conceals a fairly complex sexual relationship and life cycle. As adults, the sexes are separate and highly dimorphic. Males are reduced, dwarfed, and live attached to females as little more than a packet of sperm. Females can also reproduce asexually by budding. Males somehow also fertilize the oocyte (egg) contained within the developing female bud. Upon its release, the fertilized egg develops into a swimming chordoid larva which seems to be a modified trochophore. The choroid then seeks out other decapods and begins to mature. The female bud is motile (called a Pandora larva) and it contains the bud of a feeding stage within it. Certainly, the lifecycle of this animal is bizarre for a free-living or commensal organism. Perhaps, Symbion, the only known genus in this phylum is derived from a parasitic organism. Winnepenninckx et al. (1998) confirmed the apparent relationship between the cycliophorans , rotifers, and acanthocephalans. However, as of 2005, only one species had been discovered (Pechenik 2005). Obst et al. (2006) reported a second species of Symbion one year later and suggested that the cycliophorans might have a hidden diversity in the oceans (Obst et al. 2006). From the discovery of Cycliophora, Funch and Kristensen (1995) suggested that they were related to the Entoprocta, and that proposal was accepted by Valentine (2004), but confirmed Giribet et al. (2004) and Hejnol et al. (2009), thus uniting the Cycliophora, Entoprocta, and Ectoprocta into a higher taxon that they called Polyzoa (see Figure 2).

FIGURE 1. An illustration of Symbion. Image from http://biodidac.bio.uottawa.ca/

FIGURE 2. A cladogram showing the sister relationship between Entoprocta and Cycliophora as proposed by Funch and Kristensen (1995) together with the monophyly of the Polyzoa (Po). The overall topology of the cladogram is a modification of the Protostome relationships in Edgecombe et al. (2011). T = Trochozoa.

LITERATURE CITED Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass. Edgecombe, G. D., G. Giribet, C. W. Dunn, A. Hejnol,R. M. Kristensen, R. C. Neves, G. W. Rouse, K. Worsaae, and M. V. Sorensen. 2011. Higher-level metazoan relationships: recent progress and remaining questions. Organisms Diversity and Evolution. DOI 10.1007/s13127-011-0044-4. Funch, P. and R.M. Kristensen. 1995: Cycliophora is a new phylum with affinities to Endoprocta and Ectoprocta. Nature. 378: 711-714. Giribet, G., C. W. Dunn, G. D. Edgecombe, and G. W. Rouse. 2007. A modern look at the Animal Tree of Life. Zootaxa. 1668: 61-79. Giribet, G., M. V. Sørensen, P. Funch, R. M. Kristensen, and W. Sterrer, W. 2004. Investigations into the phylogenetic position of Micrognathozoa using four molecular loci. Cladistics. 20: 1-13. Hausdorf, B., M. Helmkampf, A. Meyer, A. Witek, H. Herlyn, I. Bruchhaus, T. Hankeln, T. H. Struck, and B. Lieb. 2007. Spiralian, phylogenomics supports the resurrection of Bryozoa comprising Ectoprocta and Entoprocta. Mol. Biol. Evol. 24(12): 2723-2729. Helmkampf, M., I. Bruchhaus, and B. Hausdorf. 2008a. Phylogenomic analyses of lophophorates (brachiopods, phoronids, and bryozoans) confirm the Lophotrochozoa concept. Proceedings of the Royal Society. B. 275(1645): 1927-1933. Helmkampf, M., I. Bruchhaus, and B. Hausdorf. 2008b. Multigene analysis of lophophorate and chaetognath phylogenetic relationships. Molecular Phylogenetics and Evolution. 46: 206-214. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York. Meglitsch, P. A. and F. R. Schramm. 1991. Invertebrate Zoology. Oxford University Press, New York, Oxford. Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford. Obst M., P. Funch, and R. M. Kristensen. 2006. A new species of Cycliophora from the mouthparts of the American lobster Homarus americanus (Nephropidae, Decapoda). Organisms, Diversity & Evolution. 6:83-97. Obst, M., P. Funch and G. Giribet. 2005. Hidden diversity and host specificity in cycliophorans: a phylogeographic analysis along the North Atlantic and Mediterranean Sea. Molecular Ecology. 14: 4427-4440. Ruppert, E. E., R. S. Fox, and R. D. Barnes. 2004. Invertebrate Zoology: A Functional Evolutionary Approach. Seventh Edition. Thomson, Brooks/Cole. New York. pp. 1-963. Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York. Valentine, J. W. 2004. The Origin of Phyla. University of Chicago Press. Chicago. 614 pp. Winnepenninckx, B., T. Backeljau, and R. M. Kristensen. 1998. Relations of the new Phylum Cycliophora. Nature. 393:636-638.

By Jack R. Holt and Carlos A. Iudica. Last revised: 04/10/2013