Phylum Phylum Annelida Annelida

By: Esther Lien

Harlan Cox

Siva Gandu

5th period

• General Characteristics– Annelids are all bilaterally symmetrical animals. They range in size from much less than 1 mm in

length to more than 3 m– Their bodies are divided into segments that may or may not be visible externally– Their body is composed of a series of ring-like segments that are specialized.– In most annelids there are usually two fluid systems, the coelom and the circulatory system, and

both (if present) are involved in the excretion of waste products.

• Classes – CLASS Polychaeta- Bristle worms– CLASS Clitellata- Leeches – CLASS Pogonophora- Beard Worm – CLASS Echiura- Spoon Worm– CLASS Oligochaeta- Earthworms

Phylum

Body Plan• Triploblastic

– is a condition of the blastula in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm

• Most remarkable advance is segmentation or metamerism• They have Elongate body which is usually round. For polychaetes and clitellidae,

the head has prostomium and peristomium which have sensory organs and feeding organs.

• Trunk segmentation appears in external annuli, and it is internally separated by coelomic compartments which are also separated by septae.

• Some are homonomous, with body segments mostly similar, others are heterononmous, with specialized segments

Feeding• For polychaetes and oligochaetes

– Raptorial• Prey captured with Head Appendages and then swallowed as a whole

– Deposit• They ingest the substrate and then they derive the nutrients from it

– Suspension• They use tentacles or mucus webs to filter nutrients from fluid environment

• Clitellata– Have a straight gut

• It has specialized organs and accessory organs, but the digestion is extracellular

• Echiura– They have a coiled gut

• The mouth is by the anus and the gut is long and coiled

• Pogonophora– Have no known digestive system

http://www.okc.cc.ok.us/biologylabs/Images/Animal_Images/annelida.jpg

Respiration

• They have no true respiratory organs.• Respiratory gas exchange through skin, gills, parapodia. • They secrete moisture from the dorsal pore • The skin has many tiny blood vessels to gather oxygen across the moist

film covering it. • Since they breathe with their whole body surface, they will suffocate if

their skin becomes dry.

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http://coris.noaa.gov/glossary/new_annelid_186.jpg

http://www.bumblebee.org/invertebrates/images/earthworm1.jpg

Circulation

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• Their blood is red because it has hemoglobin• Most annelids have closed and well-develop circulation• In certain smaller forms, the circulation is reduced or absent. They have

Coelomic canals that serve as their blood “channels”.• The enlarged and heavily muscular vessels at the anterior end serve as the

hearts that pump the blood.• Their blood is carried from dorsal to ventral vessel in the head.• Earthworms have five pulsating blood vessels that help pump blood from the

main dorsal vessel to the main ventral vessel.

Excretion• Each segment has a pair of nephridia which are long coiled ciliated tubes

to excrete their metabolic wastes.• Blood and coelomic fluid enter these tubes where nutrients, water and

salts are removed.• Their waste products are transported out of the body through the coelom

by specialized excretory tubes.

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Response• The nerve cord has two sorts of fibers: normal and giant nerves

– The nerve cord runs down the whole body .– The giant nerves are only important during rapid escape maneuvers.

• Polychaeta– Bodies organized into regions according to the function and structures.– They have a well-developed head with specialized sense organs

• Oligochaeta– They have no eyes, but they have many photoreceptors, chemoreceptors, and

mechanoreceptors that are concentrated near the ends of their body.– They have fewer setae than polychaetes and no parapodia or head region.

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http://tolweb.org/tree/ToLimages/eyes.jpg

Movement• Polychaetes

– Parapodia, paired, fleshy, paddlelike flaps, used for swimming, burrowing, or slow crawling.

– Fast crawling is performed by undulating the body.• Oligochaeta

– Chaetae – tiny hairs that provide anchoring points for burrowing

– They deform either the whole body, or segments of the body by contracting the circular and longitudinal muscles alternately

• Hirudinea– Swim with snake-like motions– Use suckers to anchor themselves to objects– Non-aqueous leeches crawl by extending and contracting

their body

Reproduction• Polychaetes

– Involves separate sexes and external fertilization, usually in water away from both parents

– Lack permanent gonads, the gamete producing sex organs– Gametes are produced from the germ cells in the lining of the coelom or in

the septa• Oligochaeta

– Hermaphrodites – each worm has both eggs and sperm– When reproducing sperm goes in both directions to and from each worm– Fertilized eggs are put in a cocoon that forms over the parent body and then

falls off• Hirudinea

– Internal fertilization within the female’s body.– A sperm sac passes over the eggs which are deposited inside

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Works Cited"Annelida." Bumblebee.org. Web. 17 Apr. 2010.

<http://www.bumblebee.org/invertebrates/ANNELIDA.htm>. Mehaffey, Leathem. "Outline for Annelids." Vassar College. 2001. Web. 17 Apr. 2010.

<http://faculty.vassar.edu/mehaffey/academic/animalstructure/outlines/annelida.html>.

Ramel, Gordon. "The Annelids (Phylum Annelida)." The Earth Life Web. Web. 15 Apr. 2010. <http://www.earthlife.net/inverts/annelida.html>.

Raven, Peter H., and Peter H. Raven. Biology. 6th ed. New York: McGraw-Hill, Higher Education, 2002. 906-09. Print.

Rouse, Greg W. "Characteristics of Annelida." Tree of Life Web Project. 2002. Web. 16 Apr. 2010. <http://tolweb.org/articles/?article_id=57>.