DESCRIPTION OF THE PHYLUM NEMERTEA

EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> METAZOA> BILATERIA> PROTOSTOMATA> SPIRALIA> TROCHOZOA> EUTROCHOZOA> NEMERTEA

Nemertea (ne-MER-ti-a) is a reference to the Greek sea nymph Nemertes (Νεμερτεσ).

INTRODUCTION TO THE NEMERTEA The ribbon worms are found in almost all environments and some are parasitic (text with tooltip) A parasite is a symbiotic organism that benefits from the relationship at the expense of the host. . They are worm-like with a characteristic evertible (text with tooltip) An evertible proboscis is a proboscis that can be extended usually by hydrostatic muscular contraction. proboscis that resides in a cavity called a rhynchocoel (text with tooltip) A rhynchocoel is a fluid-filled body cavity (coelom? pseudocoelom?) into which the nemertene evertible proboscis retracts. (Figure 1). Some are quite colorful and showy (Figure 2), and many are quite long. Lineus longissimus (Figure 3), a nemertine of the north Atlantic commonly called the boot strap worm, can exceed 30 meters in length, making it the longest animal alive. There are two major groups of Nemertea: Anopla and Enopla (Figure 4). The anoplan nemertenes have separate mouth and proboscis openings. The mouth is located below or behind cephalic anterior ganglion (“brain”). The proboscis is uniform and unarmed. Also, the gut is simple. The nervous system is within the body wall. The enoplan nemertenes have a single opening for the mouth and proboscis, which open through a common pore in front of the cephalic anterior ganglion. In this group, the nervous system is internal to the body wall musculature. Brusca and Brusca (2003) indicate that the nemertines and turbellarians share many characters ( protonephridia (text with tooltip) Protonephridia (protonephridium, sing.) are excretory organs that are ciliated tubules. The flame cell lies at the internal terminus ciliated tubule. , ocelli (text with tooltip) An ocellus (ocelli, pl.) is a simple eye or eyespot characteristic of many invertebrate groups. , epidermis, organization of the nervous system, etc). However, since these characters are primitive and shared by other phyla as well, the nemertines and turbellarians need not be related except by a common ancestor. The nemertines may not be acoelomic anyway. The rhynchocoel may be the remnant of a coelom, most of which has been lost. Indeed, Walker and Anderson (2001) state that molecular and embryological evidence suggest affinities with the Sipuncula, Mollusca, and Annelida, a position that we have taken in this system.

FIGURE 1. A nemertine with its probiscis everted. Image from http://www.ucmp.berkeley.edu/nemertini/nemertini.html	FIGURE 2. A showy banded nemertine. Image from http://www.ucmp.berkeley.edu/nemertini/nemertini.html	FIGURE 3. A preserved nemertine (Lineus longissimus), likely the longest animal on earth with records up to 30 meters. Image from the Systematics Biodiversity Image Archive

FIGURE 4. MAJOR CLADES OF THE NEMERTEA (IN THE SHADED BOX) IN THE CONTEXT OF THE PROTOSTOMATA. The general topology of the cladogram is informed by Edgecombe et al. (2011).

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. 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. Walker, J. C. and D. T. Anderson. 2001. The Platyhelminthes, Nemertea, Entoprocta, and Gnathostomulida. In: Anderson, D.T., ed. Invertebrate Zoology. Oxford University Press. Oxford, UK. pp. 59-85. [L] Valentine, J. W. 2004. The Origin of Phyla. University of Chicago Press. Chicago. 614 pp.

By Jack R. Holt. Last revised: 04/10/2013