9 Metamerism & Repd

Dr. PARVISH PANDYA’s presentation

“Metamerism & Reproduction in

Annelida”A presentation compiled from various sources by

Dr. PARVISH PANDYA,Zoology Dept. Bhavan’s College, Andheri.

Sites from which presentations have been downloaded and later editted. I am indeed thankful to them for their kindness and support :http://esg-www.mit.edu:8001/esgbio/cb/org/organelles.htmlhttp://faculty.pnc.edu/jcamp/parasit/parasit.htmlhttp://www.amnh.org/rose/hope/creatinghope/http://www.biology.eku.edu/SCHUSTER/bio%20141/POWERPOINT%20NOTES/Intro%20to%20Protozoa_files/fullscreen.htmhttp://www.biosci.ohio-state.edu/~zoology/eeob405/http://www.tulane.edu/~wiser/protozoology/pwpt/http://www.iep.water.ca.gov/suisun/photos/wildlife.htmlhttp://www.uta.edu/biology/marshall/2343/http://www.uta.edu/biology/faculty/faculty.htmlhttp://www.okc.cc.ok.us/biologylabs/Documents/Zoology/PowerPoint.htmhttp://bio.fsu.edu/http://www.aw-bc.com/http://www.nhm.org/http://www.geo.cornell.edu/eas/education/course/descr/EAS302/presentations/

It is very easy to find mistakes in these presentations…..I request you to kindly rectify them and supply me the modifications needed at parvishpandya@yahoo.comThanks a lot and have fun in teaching & learning Zoology….

Phylum Phylum AnnelidaAnnelida

PHYLUM ANNELIDAPHYLUM ANNELIDA(Annulus: Little rings)(Annulus: Little rings)

•• HABIT: Free living or HABIT: Free living or EctoparasiticEctoparasitic..•• HABITAT:Sea water, fresh water, moist soil.HABITAT:Sea water, fresh water, moist soil.•• SIZE : It varies from 1 mm to 3SIZE : It varies from 1 mm to 3 metresmetres..•• SHAPE : Body is long, cylindrical or flattened.SHAPE : Body is long, cylindrical or flattened.

What is a segmented worm?What is a segmented worm?

•Long and narrow

•Closely related to crabs and snails

•Has a body built of ring-like segments

METAMERISMMETAMERISM

MetamerismMetamerism is the phenomenon in which the is the phenomenon in which the body of an animal is divided into body of an animal is divided into anteroantero--posterior row of similar part or sections.posterior row of similar part or sections.These sections are called as segments or These sections are called as segments or metamersmetamers or or somitessomites..It involves a longitudinal division of body of a It involves a longitudinal division of body of a bilaterally symmetrical organism into a linear bilaterally symmetrical organism into a linear series of similar segments.series of similar segments.

Metamerism

•Have an anterior prostomium and posterior pygidium; both nonsegmented • Body is divided into a linear series of similar parts or segments, and each segment is called a metamere• The pattern of repeated segmentation is called metamerism• Each metamere is separated from the next by a transverse septum• Each metamere acts as a hydrostatic skeleton• Each metamere has longitudinal and circular muscles; longitudinal muscle contraction causes segments to shorten; circular muscle contraction causes segments to elongate• Each segment usually bears one or more chitinous bristles called setae;help anchor segments

TYPES OF METAMERISMTYPES OF METAMERISM

•• True & false True & false metamerismmetamerism..•• Complete and incomplete Complete and incomplete metamerismmetamerism..•• External and internal External and internal metamerismmetamerism..

Nervous System• Consists of a brain, which is connected to a pair of ventral longitudinal nerve cords, with a ganglion in each segment (metameric)

Circulatory System• Closed circulatory system, in which the blood is always enclosed within blood vessels that run the length of the body and branch to every segment• Several hearts (5 in earthworms) are used to pump blood through the closed circuit

Excretory System

• Consists of paired (metameric) metanephridia• Excretory tubes with ciliated funnels that remove waste from the coelomicfluid; open to the outside via excretory pores.

Note:Not all organ systems are metamericFor example, the digestive system extends the length of the organism and is differentiated along its length

Development

Metameric,

Coelomic

Spaces

Internal Structures of an Earthworm

NereisNereis

Sedentary Polychaete LugwormSedentary Sedentary PolychaetePolychaete LugwormLugworm

MouthMouth

AnusAnus

Sedentary PolychaeteAmphitriteSedentary Sedentary PolychaetePolychaeteAmphitriteAmphitrite

Earthworm Cross -Section

Class Polychaeta ("many bristles”)

General Characteristics

• Marine worms, including sandworms and clamworms.• Each segment is equipped with a pair of fleshy paddle-like structures -parapodia; used in locomotion• Parapodia contain a large number of chitinous bristles – setae; anchor the worms

Polychaetes: General Characteristics cont.

•Prostomium is well equipped with sensory and feeding structures

Polychaetes: General Characteristics cont.

• Mouth is located just below the prostomium, but in front of the modified segments - peristomium• Digestive system includes a muscular pharynx that can be everted through the mouth• Pharynx is equipped with pincer-like jaws

• Although many of the smaller polychaetes lack respiratory structures, the larger one do possess gills• Gills are usually modifications of the parapodia

• serial repetition of cavities and structures• transverse septa (mesoderm)• selection? • independent regulation• e.g., hydrostatic skeleton• hyp: burrowing efficiency enhanced - competitive edge

• relative energetic of cost of peristaltic waves• regional specialization - tagmatization• restriction of structures, divergence of repeated structures

Internal transport• closed• dorsal vessel is contractile (propels blood)• connected to ventral vessel at gut• hemoglobin• nephridial system• ciliated tube• uptake and removal of nitrogenous wastes• resorption of amino acids, H2O, ions

Class Polychaeta: Diversity• Although a number of polychaetes are active predators, some are sedentary and burrow into mud or live in protective tubes in themud• In several of these species filter feeding has evolved• A good example is the fan worm Sabella, with their feather-like head structures called radioles

Class Polychaeta: Diversity cont.

• Chaetopterus is tube dweller; lives in a U-shaped tube • Parapodia are highly modified into 3 fan-like structures that bring water into the tube• The notopodium secretes a mucous bag that traps food from the water flowing through the tube; the bag is periodically passed anteriorly toward the mouth

Class Polychaeta: Diversity cont.

• Arenicola lives in a J-shaped burrow• It employs peristaltic movements to generate a water flow• Food is filtered out from the front of the burrow

Class Oligochaeta cont.• Earthworms feed on vast quantities of soil that contains living and decaying organic material.• Digestive tract of the annelids shows specialization along its length: mouth, pharynx, crop (food storage), gizzard (grinding), calciferous glands (accessory glands that excrete excess calcium from the food) • Remainder of the gut is the intestine - for digestion and absorption• Its surface area is increased because of a dorsal longitudinal fold called the typhlosole

Class Oligochaeta ("few bristles")

• Many of the morphological structures are reduced when compared to the polychaetes• Prostomium lacks sensory structures• Parapodia are absent; each segment usually contains one or more pairs of setae; used in locomotion• Aquatic forms usually have larger setae than the terrestrial forms

Class Oligochaeta cont.

• Lack respiratory organs; gas exchanges occurs across the body wall• Hermaphroditic, but exchange sperm during copulation• During copulation, worms join their anterior ends; held together by mucous secretions from a clitellum• After reciprocal copulation, sperm is stored in seminal receptacles• Clitellum then secretes a mucous tube that serves as a cocoon• The cocoon moves anteriorly and eggs from the oviduct and sperm from the seminal receptacles are poured into it; fertilization occurs in the cocoon• Cocoon eventually slips off the anterior end of the worm• In time, young worms emerge from the cocoon

Class Hirudinea• Body is dorso-ventrally flattened• Anterior segments are modified as a small sucker which surrounds the mouth; posterior segments form a larger sucker• Setae are completely absent• Evidence of segmentation externally, but no internal septa• There is serial repetition of many of the organs (e.g., nephridia and testes)

tubes within tubes

dorsal vessel

c.musc.

l.musc.

septum2 layers

nephrostome

ventral vessel

nerve cord

cuticle(collagen)

epidermisglandularinnervated

G I tract

Tube Dwellers “Sedentaria”• straight or u-shaped• mucus, CaCO3 ,

sand “reefs”• modified setae• “tentacles”

gills (modified parapodia) cilia and gills move water

THEORIES ON METAMERISMTHEORIES ON METAMERISM

Different theories has been put forward because it Different theories has been put forward because it occurs both in occurs both in ArthropodaArthropoda & Vertebrates.& Vertebrates.

The various theories are as follows:The various theories are as follows:1)1) Fission theoryFission theory2)2) PseudometamerismPseudometamerism theorytheory3)3) CyclomerismCyclomerism theorytheory4)4) Embryological theoryEmbryological theory5)5) Locomotion theoryLocomotion theory

SIGNIFICANCE OF SIGNIFICANCE OF METAMERISMMETAMERISM•• LocomotionLocomotion•• BurrowingBurrowing•• ReproductionReproduction•• Rapid evolution of high grade of Rapid evolution of high grade of

organizationorganization

REPRODUCTIONREPRODUCTION

•• It takes place both asexually & sexually.It takes place both asexually & sexually.•• Asexual reproduction occurs without the Asexual reproduction occurs without the

fusion of male and female gametes.fusion of male and female gametes.•• Sexual reproduction takes place by the Sexual reproduction takes place by the

fusion of male and female gametes(sex fusion of male and female gametes(sex cells).cells).

Reproductive System

• Most annelids are hermaphroditic, but they are usually cross fertilizers.• Earthworms and leeches form pairs and reciprocally fertilize one another• Some annelids (e.g. marine sandworms) are dioecious and they release eggs and sperm into the marine environment, where gametes unite to form trochophore larvae

ASEXUAL REPRODUCTION ASEXUAL REPRODUCTION

•• PolychetesPolychetes & & aqaq..oligochetesoligochetes show asexual show asexual reproduction.reproduction.

•• Budding & fragmentation occurs in Budding & fragmentation occurs in polychetespolychetes..

•• Fragmentation is divided into two Fragmentation is divided into two types:a)Orderly and b)Spontaneous. types:a)Orderly and b)Spontaneous.

SEXUAL REPRODUCTIONSEXUAL REPRODUCTION

•• It is shown by all the three type classIt is shown by all the three type class•• Class Class polychaetapolychaeta e.g. Aphrodite, e.g. Aphrodite,

AmphitriteAmphitrite, , ArenicolaArenicola etc.etc.•• Class Class oligochaetaoligochaeta e.g. Pheretima.e.g. Pheretima.•• Class Class hirudineahirudinea e.g. e.g. HirudinariaHirudinaria..

Earthworm Reproduction

Class Hirudinea con’t

• Leeches are hermaphroditic but engage in cross-fertilization; some use hypodermic impregnation• Leeches have a clitellum and are capable of generating a cocoon

Reproduction• dioecious• epitoky• atokes bud epitokes• dispersal -> mating• trocophore larvae

MouthMouthMouth

AnusAnusAnus

Trochophore larvaTrochophoreTrochophore larvalarva Apical tuftApical tuftApical tuft

StomachStomachStomach

Ciliary bandCiliaryCiliary bandband

Annelid developmentAnnelid developmentAnnelid development

The EndThe End

9 Metamerism & Repd

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