EUTROCHOZOA

TAXA OF LIFE	KINGDOM ANIMALIA
PHYLUM NEMERTEA

INTRODUCTION TO THE NEMERTEA

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

The ribbon worms are found in almost all environments and some are parasitic. They are worm-like with a characteristic evertible proboscis that resides in a cavity called a rhynchocoel (Figure A). Some are quite colorful and showy (Figure B), and many are quite long. Lineus longissimus (Figure C), 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. 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.

A. A nemertine with its proboscis everted (top).

B. A showy banded nemertine.

C. A preserved nemertine (Lineus longissimus), likely the longest animal on earth with records up to 30 meters.

Images taken from:
A&B: http://www.ucmp.berkeley.edu/nemertini/nemertini.html
C: From the Systematics biodiversity image collection.

SYNOPTIC DESCRIPTION OF THE NEMERTEA

The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Storer and Usinger (1965), Tudge (2000), and Walker and Anderson (2001).

I. SYNONYMS: ribbonworms, rhynchocoels, nemertines.

II. NUMBER: >900 species known.

III. PHYLUM CHARACTERISTICS:

A. Structure

Symmetry: Bilateral

Body Cavity: Not present. Organ systems in parenchymatous mesoderm. Evertible proboscis in a cavity called a rhynchocoel, dorsal to the intestine.

Body Covering: Ciliated epithelium.

Support: Hydrostatic skeleton.

Digestive System: Complete food tube with mouth and anus. Captures food with an evertible proboscis, often armed with a stylet at the tip.

Circulatory System: Blood vessel system in parenchymal mesoderm.

Locomotion: Ciliated epithelium and muscular contractions.

Excretory System: Specialized excretory canals.

Nervous System: Anterior ganglion with 2 major lateral nerves.

Endocrine System: None.

B. Reproduction:

Reproductive System: Most are dioecious. Oviparous.

Development: Zygote develops into pilidium or desor larva with a flatworm-like gut.

C. Ecology: Freshwater, marine, or terrestrial. Some are commensals or parasites. Usually carnivores. Marine species are usually benthic.

SYSTEMATICS OF THE NEMERTEA

Brusca and Brusca (2003) indicate that the nemertines and turbellarians share many characters (protonephridia, ocelli, 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.

HIERARCHICAL CLASSIFICATION OF THE NEMERTEA

Taxonomy of the Phylum follows the system of Brusca and Brusca (2003). Descriptions of the following taxa were taken from Brusca and Brusca (2003), Hickman (1973), Storer and Usinger (1965), Tudge (2000), Valentine (2004), and Walker and Anderson (2001).

CLASS ANOPLA (2 ORDERS)

Separate mouth and proboscis openings; mouth below or behind cephalic anterior ganglion. Proboscis uniform and unarmed. Gut simple; nervous system within body wall.

Carinoma, Hubrechtella, Tubulanus, Cepahalothrix, Baseodiscus, Lineus, Cerebratulus, Micrura, Paralineus.

CLASS ENOPLA (2 ORDERS)

Mouth and proboscis open through common pore in front of ganglion; nervous system internal to body wall musculature.

Annulonemertes, Carcinonemertes, Emplectonema, Geonemertes, Paranemertes, Prostoma, Amphiporus, Hubrechtonemertes, Nectonemertes, Pelagonemertes, Malacobdella.

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. 3^rd 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: 01/28/2009