DESCRIPTION OF THE PHYLUM ENTOPROCTA (NITSCHE 1870)
| EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> BILATERIA> PROTOSTOMATA> SPIRALIA> TROCHOZOA> POLYZOA> ENTOPROCTA |
ENTOPROCTA LINKS
| Entoprocta (en-to-PROK-ta) is made of two Greek roots that mean anus on the inside [within -endon (ένδον); anus -proktos (πρωκτός)]. The reference is to the placement of the anus within the ring of lophophores. The name for the group was coined by Nitsche (1870). |
| INTRODUCTION TO THE ENTOPROCTA The entoprocts bear a strong resemblance to the Ectoprocta. Both groups usually live in sessile (text with tooltip) Sessile is sedentary or attached to a substrate. colonies of cup-shaped zoids (Figures 1-3) which have ciliated tentacles (lophophores) that function to filter out food particles. Like the ectoprocts, the entoprocts have a complete digestive tract, but in the Entoprocta, both the mouth and anus occur within the lophophore ring (Figure 4). An important difference is that the entoprocts lack a true coelom, a condition that is blastocoelic, also called pseudocoelomate. Other differences between the two taxa include the direction of water flow created by the lophophores (water moves from the bottom to the top of the lophophore tentacles in the entoprocts, movement is reversed in the ectoprocts). They also differ in the occurrence of protonephridia in entoprocts (ectoprocts have no nephridial organs). Thus, they appeared to be only superficially similar. The developmental history of the entoprocts clearly shows affinities with the Spiralia. Most importantly, they have determinate, spiral cleavage. Also, the entoprocts have a trochophore or trochophore-like larva. The confusion in the literature regarding the monophyly of Bryozoa (Entoprocta + Ectoprocta) stemmed from the question of the type of coelom and was further exacerbated by an early molecular phylogenetic study (Mackey et al. 1996) in which 18S rRNA comparisons implied that the ectoprocts and entoprocts were not monophyletic. Therefore, Brusca and Brusca (2003) and Nicholas (2001b) considered them to occupy separate phyla, but Tudge (2000), Nielsen (2001), and Margulis and Schwartz (1998) did not. Valentine (2004) declared that the two taxa occupy separate major clades of the protostomes and only superficially resemble each other. Giribet et al. (2007) have placed the entoprocts within the lophotrochozoans (=Spiralia) and removed the Ectoprocta (Bryozoa) to an equivocal position between the Paracoelomata (=Platyzoa) and the Lophotrochozoa (=Trochozoa). More recently, Hausdorf et al. (2007) and Helmkampf et al. (2008a and 2008b) used phylogenomic analyses and confirmed that Ectoprocta and Entoprocta form a monophyletic clade. From the discovery of Cycliophora, Funch and Kristensen (1995) suggested that they were related to the Entoprocta, and that proposal was confirmed by Giribet et al. (2004) and Hejnol et al. (2009), thus uniting all three taxa into a higher taxon that they called Polyzoa (see Figure 5). |
 |  |  |  |
| FIGURE 1. Bartensia, a common marine colonial entoproct. Image from http://animaldiversity.ummz.umich.edu/site/accounts/pictures/Entoprocta.html | FIGURE 2. Urnatella, an entoproct found in freshwater. Image from http://animaldiversity.ummz.umich.edu/site/accounts/pictures/Entoprocta.html | FIGURE 3. An illustration of Pedicellina. Image from http://biodidac.bio.uottawa.ca/ | FIGURE 4. A longitudinal section through the zoid of Pedicellina. Note the complete digestive tract with the mouth (L) and anus (R), both opening within the tentacular ring. Image from http://biodidac.bio.uottawa.ca/ |
 | FIGURE 5. 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 Barnes, R. D. 1980. Invertebrate Zoology. Saunders College/Holt, Rinehart and Wilson, Philadelphia. Barnes. R. S. K. 1984a. Kingdom Animalia. IN: R. S. K. Barnes, ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc., Sunderland, MA. pp. 129-257. Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass. Buchsbaum, R. 1938. Animals Without Backbones, An Introduction to the Invertebrates. The University of Chicago Press. Chicago. Dunn, C.W., A. Hejnol, D.Q. Matus, K. Pang, W.E. Browne, S.A. Smith, E. Seaver, G.W. Rouse, M. Obst, G.D. Edgecombe, M.V. Sørensen, S.H.D. Haddock, A. Schmidt-Rhaesa, A. Okusu, R.M. Kristensen, W.C. Wheeler, M.Q. Martindale, and G. Giribet. 2008. Broad phylogenomic sampling improves resolution of the animal tree of life. Nature. 452: 745-749. 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. Fuchs, J. M. Obst, and P. Sundberg. 2009. The first comprehensive molecular phylogeny of Bryozoa (Ectoprocta) based on combined analyses of nuclear and mitochondrial genes. Molecular Phylogenetics and Evolution. 52(1): 225-233. 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. Hickman, C. P. 1973. Biology of the Invertebrates. The C. V. Mosby Company. Saint Louis. Mackey, L. Y., B. Winnepenninckx, R. DeWachter, T. Backeljau, P. Emschermann, and J. R. Garey. 1996. 18S rRNA suggests that Entoprocta are protostomes, unrelated to Ectoprocta. Journal of Molecular Evolution 42:552-559. 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. Nicholas, W. L. 2001b. The pseudocoelomate Ecdysozoa. In: Anderson, D.T., ed. Invertebrate Zoology. Oxford University Press. Oxford, UK. pp. 98-119. Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford. Nitsche, H. 1870. Beobachtungen über die Entwicklungsgeschichte einiger chilostomen Bryozoen. Zeitschr. zeiss. Zool. 20: 1-37. Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. 6th edition. Saunders. Ft Worth, TX. 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. Storer, T. I. and R. L. Usinger. 1965. General Zoology. 4th Edition. McGraw-Hill Book Company. New York. 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. |
| By Jack R. Holt and Carlos A. Iudica. Last revised: 02/17/2019 |
