DESCRIPTION OF THE PHYLUM PHORONIDA (HATSCHEK 1888)
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PHORONIDA LINKS
| Phoronida (fo-RON-i-da) is derived from a single Greek word that means Isis, the Egyptian goddess [Phoronis (φορονισ)]. The name was coined by Hatschek (1888). |
| INTRODUCTION TO THE PHORONIDA The phoronids are filter-feeding benthic (text with tooltip) A benthic (adj.) organism is one that lives in or on the bottom of marine or freshwater environments. invertebrates that have a lophophore system similar to that of the brachiopods. They live in a tube that they secrete and is buried in loose substrate; so, only the anterior end emerges when feeding (Figures 1 and 2). The phoronids are now made up of two genera; however, they seem to have been quite important during the Cambrian and were among the dominant animals found in the Burgess Shale. The phoronids have a true coelom. Internally, the body is divided into three regions: a small preoral lobe or epistome (text with tooltip) The epistome is a part of the head in different arthropods. It is the region behind the mouth in insects and between the antennae and the mouth in crustaceans. It also is the preoral lobe of phoronids. that overhangs the mouth, a short mesosome (text with tooltip) The mesosome is a body region in phoronids that bears the lophophores. that bears the lophophore; and a long cylindrical trunk. The trunk, mesosome (and possibly epistome) all have enterocoelic body cavities. The coelom is well-developed and even extends into the tentacles of the lophophore. The characters of the living members of the phylum are similar to those of the Phylactolaemata Ectoprocts. Very likely, the ectoprocts evolved from a phoronid line that became colonial. Brusca and Brusca (2003) and Margulis and Schwartz (1998) assume that the relationship between the lophophorate groups (bryozoans, brachiopods, and phoronids) is natural. However, Nielsen (2001) considers the lophophorate condition to be ancestral in the clade of the Bilateria. Indeed, Tudge (2000) includes them in a protostome group called the Lophotrochozoa. If this is true, the lophophorates cannot exist as a natural unit as is suggested by the Animal Tree of Life of Giribet et al. (2007). As with the brachiopods, the developmental history of the phoronids is similar to that of the deuterostomes such that Nielsen (2001) and Margulis, Schwartz (1998), and Brusca and Brusca (2003) place them into that group (this is consistent with most of the earlier work on brachiopods). Certainly more extensive developmental, structural, and molecular studies will be required to sort this out. Halanych et al. (1995) first suggested a relationship between Phoronida and Brachiopoda by analyses using 18S rDNA. The relationship held consistently such that (Cohen 2000) made the phoronids a valveless subclass of the brachiopods. We have kept the Phoronida as a sister group to the Brachiopoda in a clade called Brachiozoa (Figure 3). |
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| FIGURE 1. A field of Phoronopsis with only their anterior ends above the substrate. Image from: http://www.horta.uac.pt/species/Phoronida/Phoronopsis_harmeri/Phoronopsis_harmeri.htm | FIGURE 2. Phoronopsis removed from their tubes. Image from: http://www.ucmp.berkeley.edu/brachiopoda/phoronida.html |
 | FIGURE 3. Placement of the Phoronida within the protostomes. T = Trochozoa B = Brachiozoa |
| 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. 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. Hatschek, B. 1888. Lehrbuch der Zoologie, 1. Lieferung. Gustav Fischer. Jena. pp. 1–144. Hickman, C. P. 1973. Biology of the Invertebrates. The C. V. Mosby Company. Saint Louis. 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. 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. |
| By Jack R. Holt. Last revised: 04/10/2013 |
