SYNOPTIC DESCRIPTION OF THE PHYLUM ANNELIDA
| EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> METAZOA> BILATERIA> PROTOSTOMATA> SPIRALIA> TROCHOZOA> EUTROCHOZOA> ANNELIDA |
ANNELIDA LINKS
| The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Meglitsch and Schramm (1991), Ruppert and Barnes (1991), Storer and Usinger (1965), Valentine (2004), and Tudge (2000). |
I. SYNONYMS: segmented worms.
II. NUMBER: >15,000 species known.
III. PHYLUM CHARACTERISTICS:
- A. Structure
- Symmetry: Bilateral; anterior prostomium (text with tooltip) The prostomeum is the segment anterior to the mouth in annelids. , posterior pygidium (text with tooltip) The pygidium was the terminal tegma of trilobites; usually, a fused terminal shield, which was strong and the most common portion preserved as fossils. It is the fused terminal segments of annelids. , and in between them a series of metameric segments (text with tooltip) Metameric segments are body segments that are repeated and identical. . Pogonophoran body divided into 4 regions – a cephalic lobe, a region which secretes the tube, a trunk and a segmented opisthosome.
- Body Cavity: True coelom, but highly reduced in some. Schizocoelic (text with tooltip) Schizocoelic (adj.) describes a type of true coelom that develops by the separation of mesoderm tissue. within each segment in most. Schizocoelic within the trunk of echiurids and sipunculids.
- Body Covering: Covered by cuticle (text with tooltip) Cuticle is an acellular covering that is secreted by the epithelium. , chitinous spines or setae usually project from each segment. Echiurid proboscis with a ciliated groove.
- Support: Hydrostatic skeleton.
- Digestive System: Food tube simple, lined with gastrodermis. Absorptive surface increased by presence of typhlosole (text with tooltip) The trochophore is a fold into the lumen of the annelid gut and serves to increase the absorptive area of the gut wall. . Mouth at anterioventral and anus terminal. Pharynx sometimes eversible with jaws. Echiurids with extendible proboscis (it cannot be retracted within the trunk) with mouth at its base. Pogonophorans without a food tube. Sipunculids feed by ciliated tentacles and have a U-shaped digestive tract.
- Circulatory System: Closed (text with tooltip) A closed circulatory system has veins and arteries connected by capillary beds. Thus, the blood elements are contained within vessels. . Dorsal and ventral major vessels connected by segmented connections that may act as hearts. Some have respiratory pigments dissolved in plasma; some cells with hemoglobin.
- Locomotion: Animals move by differential hydrostatic pressure in the segments in concert with the setae or by whole body movements.
- Excretory System: Pairs of metanephridia (or protonephridia (text with tooltip) Protonephridia (protonephridium, sing.) are excretory organs that are ciliated tubules. The flame cell lies at the internal terminus ciliated tubule. ) per segment.
- Nervous System: A prostomial brain, a pair of ventral nerve cords, usually connected by ganglia (text with tooltip) A ganglion (ganglia, pl.) is a cluster of nerve cells. A brain is an enlarged ganglion. at each segment. Sensory organs may be complex; eyes and tentacles.
- Endocrine System: None.
- B. Reproduction:
- Reproductive System: Dioecious (text with tooltip) Dioecious organisms have separate male and female individuals. or hermaphroditic (text with tooltip) An animal that bears both male and female gonads. . Fertilization external or internal.
- Development: Zygote develops by spiral cleavage (text with tooltip) Spiral cleavage is typical of the Protostomata and is characterized by the division planes of early cytokinesis products of the zygote being oblique to the plane of the polar axis. This produces unequal cells in the developing blastula. Usually spiral cleavage is determinant. into a prostomatous embryo; some with trochophore larva (text with tooltip) The trochophore larva is a distinctive larval form of an assortment of protostomes (e.g. annelids, mollusks, bryozoans). Commonly found in the marine plankton, the trochophore is top-shaped with a marginal ring of cilia pygidium and a ciliary tuft near the mouth. . Sipunculids develop pelagic larva ( pelagosphaera (text with tooltip) The pelagosphaera is a distinctive larval form of the sipunculids. Clearly, it is a modified trochophore larva. ) after the trochophore.
- C. Ecology: Mostly free-living, terrestrial and aquatic (marine and freshwater). Many live in the bottom mud. Pogonophorans are sessile marine saprobes, often near deep ocean vents.
| 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. Conway Morris, S. and J. S. Peel. 2008. The earliest annelids: Lower Cambrian polychaetes from the Sirius Passet Lagerstätte, Peary Land, North Greenland. Acta Palaeontol. Pol. 53(1): 137-148. Darwin, C. R. 1881. The Formation of Vegetable Mould, Through the Action of Worms, With Observations on their Habits. John Murray. London. Frelich, L., C. Hale, S. Scheu, A. Holdsworth, L. Heneghan, P. Bohlen, and P. Reich. 2006. Earthworm invasion into previously earthworm-free temperate and boreal forests. Biological Invasions. 8(6): 1235-1245. 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. Halanych, K. M. 2004. The new view of animal phylogeny. Annu. Rev. Ecol. Evol. Syst. 35: 229-256. Halanych, K. M., T. G. Dahlgren, and D. McHugh. 2002. Unsegmented annelids? Possible origins of four lophotrochozoan worm taxa. Integ. and Comp. Biol. 42: 678-684. 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. McHugh, D. 1997. Molecular evidence that echiurans and pogonophorans are derived annelids. Proc. Nat. Acad. Sci. USA. 94: 8006-8009. 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. Pechenik, J. A. 2005. Biology of the Invertebrates. McGraw-Hill. New York. 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. Siddall, M. E., E. Borda, and G. W. Rouse. 2004. Toward a tree of life for Annelida. In: Cracraft, J. and M. J. Donoghue, eds. Assembling the Tree of Life. Oxford University Press. Oxford, New York. pp. 237-251. Storer, T. I. and R. L. Usinger. 1965. General Zoology. 4th Edition. McGraw-Hill Book Company. New York. Struck, T. H., N. Schult, T. Kusen, E. Hickman, C. Bleidorn, D. McHugh, and K. M. Halanych. 2007. Annelid phylogeny and the status of Sipuncula and Echiura. BMC Evolutionary Biology. 7:57 doi: 10.1186/1471-2148-7-57 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. Zrzavý, J., P. Ríha, L. Piálek, and J. Janouskovec. 2009. Phylogeny of Annelida (Lophotrochozoa): total-evidence analysis of morphology and six genes. BMC Evolutionary Biology. 9:189 doi: 10.1186/1471-2148-9-189 |
| By Jack R. Holt. Last revised: 01/25/2012 |
