Phylum Annelida

Annelid Characteristics“annulatus” = ringedMetamerism =>not limited toexternal,schizocoelous, vermiformProtostomesSuccessful invaded all moistenvironmentsSegments arise throughteloblastic growthHead & tail = not consideredsegments

General AnatomyMetameres = annuliHomonomous vsheteronomous =regional specializationsetaeGut separated from bwby coelomSegmentation internallyEversible pharynx withjaws or proboscisComplete digestivetractMeta-or protonephridia

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1. Dorsal blood vessel 4. Gut 2. Longitudinal muscles 5. Ventral nerve cord3. Coelom 6. Ventral blood vessel

Mircoanatomy

General Feeding/DigestionComplete gut (onewayfood movement),mesodermalMouth -> buccal cavity(pharynx) -> esophagus(crop/gizzard) ->intestine -> rectum ->anusProtease, carbohydrase,lipase, even cellulaseDigestion predominantlyextracellularFeeding = great diversityin form and function

Respiration/Circulation/ExcretionNone to many gillsWhen none = whole body ordorsal surfaceGills associated with parapodia,i.e. 2-3 paired or fanlike gillsRespiratory pigmentshemoglobin, -erythrin andchlorocruorin

Closed circulation, dorsal(anterior)/ventral (posterior) bvUnidirectional flow by valves

Metanephridia, pair/segment

Nervous System/Sensory Organs1. Anterior ganglion2. Circumesophagealconnectives3. Single median nerve cord4. Giant motor axons

1. Eyes = prostomium2. Chemoreceptors3. Touchreceptors4. Vibration receptors5. Statocysts6. Proprioceptors7. Nuccal organ

Reproduction/Early Development1. Asexual = uncommon,fission2. SexualDiecious, externalSpawning controlledhormonallyFormation of epitokeGamete release =nephridiophoreCopulation

Spiral development, zygote

Early trochophore Trochophorelarvae ofdifferentpolychaetespecies.

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1. Apical tuft2. Mouth3. Stomach4. Ciliary band5. Anus

Typical Protostome Larvae: Trochophore

Later stage trochophores. The specimen on theright has already three segments.No typicsl metamorphosis but growth bysegment addition.

Typical Protostome Larvae: Trochophore

Annelid Taxonomy

ClassPolychaeta

Photo of the anterior end ofthe clam worm, Nereis.

1. Prostomial tentacles2. Palp 3. Peristomial tentacles4. Prostomium 5. Peristomium

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Photo of a parapodium of Nereis.

Biramous appendageVentral neuropodium and a dorsal notopodiumEach supported by a stiff chitinous rod = aciculumDorsal and ventral cirrus projectdark staining setae extend beyond the parapodium

1. Dorsal cirrus2. Notopodium3. Setae4. Neuropodium5. Ventral cirrus6. Acicula

Polychaete Jaws

Identifying characteristics for polychaeteOften distinct only on EM level

The sedentary polychaetes are the “couchpotatoes” that live in fixed tubes andoften do not contain parapodia, sensorystructures and a distinc head.

Sedentia

Sedent ia Err antia Body Segments Limit ed number,

may be separated into diff ere nt regions

A large number

Anter ior Appendag es

May be absent or few to many simil ar appendages

Few in number and diff ere ntia ted in to pa lps, antennae, cirri etc.

Lif e Habit Burrowing Free li vin g a nd generally rapacious

Feeding Mode Filt er fee din g All wit h jaws

Clam worms (Nereis) crawl about on the oceans floorhunting for food using well-developed sensorystructures. Once located, prey are seized with chitinousjaws on a rapidly everted, muscular pharynx.

This is an image of anerrant (mobile)polychaete Nereis.

Errantia: Predators

Blood worms (Glycera) are gallery dwellers, “sit and wait”or “lurking” predators with an eversible pharynx (1/2 to1/3 total animal length with4 black jaws equipped withvenom glands.

This is an image of anerrant (mobile)polychaete Glycera(Japan).

Errantia: Predators

Lugworms (Arenicola) live in L-shaped burrows in softsubstrate and draw water into their tube to create afeeding current. They separate organic from inorganicparticles in their pharynx which is unarmed but mucouscovered.

Errantia: Direct Deposit FeedersThese are images of the tubes and the live animalArenicola.

Bamboo worms (Clymenella torquata) live in L-shapedburrows in soft substrate and draw water into their tubeto create a feeding current. They separate organic frominorganic particles in their pharynx which is unarmed butmucous covered.

Errantia: Direct Deposit Feeders

This is an image ofan errantpolychaeteCymenella torquata.

Terebellids have mucous covered ciliated tentacles whichare curled into gutters. Ciliary beats cause food particlesto be moved into the mouth.

Errantia: Selective Deposit Feeders

This is an image of aTerebellid worm(Polychaeta).

Feather duster worms (Sabellids) have radioles (pennatestructures) which are ciliated and mucous covered.Particles get trapped on mucous and moved by ciliary beatto the midrib. The midrib contains gutters that separateparticles according to size.

Errantia: Suspension Feeders

This is an image ofSabella.

Parchment worms (Chaetopterus variopedatus) live in U-shaped tubes and contain aliform (wingshaped) parapodiawhich are mucous covered and created a feeding current.Particles stick to mucous and are rolled up to form foodbolus.

Errantia: Filter Feeders

This is an image ofChaetopterus variopedatus.

Class Oligochaeta

Pharynx

Esophagus

Calciferous Glands

Crop

Gizzard

Intestine

Class OligochaetaNo biramous appendages, contain seatae, lack ofcephalization, movement through peristalsis, digestiveregional specialization

1. Cuticle 3. Dorsal blood vessel2. Longitudinal muscles 4. Chloragogue tissue

5. Intestinal lumen

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51. Setae2. Cuticle3. Hypodermis 4. Circular muscle layer5. Longitudinal muscle layer

Class Oligochaeta

Class Hirudinea

Superficial annulation, dorsoventrally flattened, twopronounced suckers, ectoparasites, may containproboscis

Class Hirudinea