KINGDOM ANIMALIA
| SYSTEMATIC BIOLOGY |
KINGDOM ANIMALIA |
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| HOME | SYLLABUS | WEEKLY ASSIGNMENTS | J. SYSTEMATIC BIOLOGY | TAXA OF LIFE | |
| PHYLUM 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. 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.
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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. |
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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). |
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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. |
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), and Walker and Anderson (2001). |
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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. |
This page is maintained by Jack R. Holt. Last modified: 01/07/08
