General IntroductionThe Annelids (Latin anellus ="little ring) are a large phylum comprising of segmented worms.About 15,000 modern species (including the earthworms and leeches). Found in most wet environments (freshwater & most marine).Most prefer aquatic but some are terrestrial.Some are parasitic or mutualistic. Range in length from under a millimeter to over 3meters.Feed a wide range of material ingest sediments and blood-suckers.

Species commonly known to human beings: The Rain, Dew or Earthworms that work so hard to make our soils healthy.

The Ragworms and Lugworms used by marine fishermen.

Tubifex or Red worms used by aquarists to feed their fish.

Leeches for medicinal purposes.

Fan Worms & Bristle worms Polychaetes

General charateristicsBilaterally symmetrical and vermiform.

Body has more than two cell layers, tissues and organs.

Body cavity is a true coelom, often divided by internal septa.

Body possesses a through gut with mouth and anus.

Body possesses 3 separate sections, a prostomium, a trunk and a pygidium.

Has a nervous system with an anterior nerve ring, ganglia and a ventral nerve chord.

Has a true closed circulatory system.

Has no true respiratory organs.

Reproduction normally sexual and gonochoristic (a distinct sex) or hermaphoditic.

Phylum Annelida*Annelid CharacteristicsDefining CharacteristicsOne or more pairs of chitinous setaeThe phylum includes polychaetes, earthworms, leeches, and vestimentiferansTrue segmented wormsMetameric segmentation

Phylum Annelida*Body StructureThe body is a tube within a tube

The coelom is important to annelids for:

The epidermis is what secretes the tough cuticle

Annelid Body PlanSetae

Phylum Annelida*LocomotionOn each side of the animal is a parapod (parapodia) consisting of fleshly lobes, which are supported by chitinous rodsEach parapod have setae, which can be sharp (protection), and aid in locomotion

Phylum Annelida*FeedingAnnelids range from carnivores, herbivores, scavengers, deposit feeders, and filter feedersWith very few defenses, many remain in a burrow or secreted tube Carnivores can capture prey with strong jaws and quickly drag it back to its burrowCan use a muscular pharynx = eversible proboscis

Phylum Annelida

Phylum Annelida*Digestive System

Phylum Annelida

Phylum Annelida*Circulatory SystemBlood flows entirely in closed vesselsSome spp. have hearts

Blood contains hemoglobin, which increases oxygen carrying ability

Phylum Annelida*Excretory & Nervous System

Phylum Annelida*ReproductionSexes are usually separate with gonads occurring in each segmentSome species have gonad specific segmentsBreeding is usually seasonal (spring or fall)As gametes mature they fill the coelom and are released by the nephridiaFertilization can be internal or external Trochophore larvae develop, which are remarkably similar to the Molluscs

Phylum Annelida

Asexual reproductionAsexual fragmentation - allows them to reproduce quickly. (e.g. Lumbriculus blackworm)

The body breaks off and forms a new identical worm. Each surviving fragment undergoes rapid regeneration of body segments to form a new head end, tail end, or both ends.

Each fragment grows into a normal sized worm comprising a combination of older and newer segments, representing two or more generations of development.

Never reach maturation / produce coccoons

Many other taxa (eg. most earthworms) cannot reproduce this way, though they can regrow amputated segments.

Sexual reproductionEarthworms, oligochaetes and leeches are hermaphroditic and mate periodically throughout the year in favoured environmental conditions.

Mate by copulation.

Two worms which are attracted by each other's secretions lay their bodies together with their heads pointing opposite directions.

The fluid is transferred from the male pore to the other worm.

Sperm transfer varies across genera, and may involve internal spermathecae (sperm storing chambers) or spermatophores that are attached to the outside of the other worm's body.

Phylum Annelida*Taxonomic SummaryPhylum AnnelidaClass PolychaetaFamily SiboglinidaeClass ClitellataSubclass OligochaetaSubclass Hirudinea

Classification

Annelid Phylogeny

Class Polychaeta - largest group of annelids and the majority are marine (Fan worms, Bristle worms etc.).

Class Clitellata Oligochaeta includes earthworms which are both aquatic and terrestrial, and tubificids. As traditionally defined, the Oligochaeta are paraphyletic. Leeches (Hirudinea) - These include both bloodsucking external parasites and predators of small invertebrates. Acanthobdellidea and Branchiobdella - small leech-like clitellates.

Class PolychaetaMost common marine organisms - colourful annelids of the sea

More than 10,000 species.

Living in the depths of the ocean, floating free near the surface, or burrowing in the mud and sand.

One common feature - Polychaetes have bristles on their legs.

Generally medium size < 10cm in length and 2 to 10mm diameter - Some, such as Eunice gigantea, may reach 3m long.

Phylum Annelida*Class PolychaetaDefining characteristicsParapodia?Some tube species lack parapodia but it is believed to have been lostParapodia differ from species to species and play an important role in identification

Class PolychaetaHighly specialized head regionsAntennaeSensory palpsFeeding appendagesPaired extensions of body (parapodia)Often tube-dwellingBurrow into substrate and secrete mucus

Bispira bunneasabellid worm

Polychaete Anatomy

Polychaete Anatomy (cross section)

used for movement

act as primary respiratory surfaces (external gills)

Parapodial muscles attach to circulairParapodiaChaetae Each parapodium 2 bundles of chaetae

New chaetae produced by chaetal sac when older chaetae lost or shed

Chaeta used to improve traction for locomotion through sediment or over surfaces

Tips of chaeta needles/hooks/serrated blades

Some chaeta spatule shovels for digging

Some chaeta - swimming

Wheres the head??Head region of polychaete prostomium + peristomium and one or more additional segments

Peristomium has sensory tentacular palps

Nervous system and sense organsBrain varies in structure, with mobile active forms having the most complex brains, and sessile or burrowing forms having simple brains with little differentiation.

Brain is connected to the ventral nerve cord by the circumpharyngeal connectives, which run down each side of the pharynx (part of the digestive tract just after its mouth).

Sense organs of Polychaetes 6 major sensory structures palps, antennae, eyes (ocelli), statocysts, nuchal organs and lateral organs

Palps and antennae are located on the head of many polychaetes. In some groups they are both sensory while in others the palps are used for feeding.

Nuchal organs are ciliated, paired, chemosensory structures, innervated from the posterior part of the brain detecting food

Sensory appendages of prostomium (antennae, palps), peristomium (tentacular cirri), parapodia (dorsal and ventral cirri), pygidium (pygidial cirri) sensory cells

Mechanoreceptors, chemoreceptors

Eyes (ocelli) located at the feathers of some feather duster worms can detect shadow

Circulatory systemA closed circulatory system is present in most polychaetes

Major blood vessels are present but the distal capillary vessels are missing in a number of polychaete groups.

A circulatory system is absent in many small polychaetes.

Digestive systemGut straight tube from mouth to the anus contain digestive enzymes

Pharynx, short esophagus, stomach, Intestines, rectum

Teeth some species grasping jaws in pharynx

Worms crawl or burrow feces released and abandoned

Tube-dwelling polychaetes pump water unidirectionally through tubes defecate into downsteam exhaust flow

Some avoid fecal contamination by living upside down in vertical tubes feather duster worms has ciliated groove transports fecal pellets from anus anteriorly out of tube

Many species consolidate their feces into high density fecal pellets or strings - tend not to resuspend or reenter burrow or tubes

Ways of feedinglying in its burrow and continually ingesting sand (up to 23 hours a day!). Arenicola (Arenicolidae)

Comprised of many radioles which are modified grooved palps.

Each radiole has pinnules that are lined with cilia and these create a current in the surrounding water.

The current passes through the radioles and food particles are trapped on the pinnules and carried into the ciliated groove by cilia.

The ciliary current carries the particles towards the base of the radioles where the material is sorted. The feathery crown of sabellids

living in a burrow with palps extended for gathering food.

Food particles are collected in the grooved palps which have cilia as well as mucus.

The palps are drawn back to the mouth region where they are 'wiped clean' by the upper lip and ventral buccal organ. Terebellid polychaete

Body wall and tubes of polychaetesTube material fibrous protein appearance of cellophane, parchment or silk barrier for protection or feeding (catch passing prey)

Incorporate mud, quartz, sand, shell fragments, plant debris and algae into wall of tube

A worm may permanently occupy its tube enlarging growth. (eg. Chaetopterus and feather-duster worms)

Or maybe abandon the tube, crawl to new location and secrete another. (eg. Diopatra)Diopatra cuprea (Plumed worm)

divided into 2 groups Active, mobile species - swim/crawlCircular muscles play a minor roleAction of parapodia - crawlingAcicula (chitinous support rods within parapodia) play an important role stiffening elementscilia

burrowing speciesSpend their lives in simple burrows in sediment or in protective tubesParapodia greatly reduced, some species absentAcicula are absent Lack protusible pharynx Locomotion

Tubeworms submerged in a pool and exit from its tube to have a quick look around.

Phylum Annelida*Polychaete LifestylesCrawling polychaetesPelagic polychaetes Burrowing polychaetesTube-dwelling polychaetes

Phylum Annelida

PolychaetaAmphitrite

Arenicola sp.Lugworm (Arenicola sp)

Sabellid Polychaeta

Chaetopterus sp.

Siboglinidae (formerly - Phylum Pogonophora)Ridgea sp

Giant tube worms (Vestimentifera)Riftia pachyptila trophosome

Bobbit wormsEunice spp.

Feather-duster worms

Polychaete ReproductionDioeciousTrochophore larvae

Some species develop specialized segments containing gametesEpitokesSegments are released and gametes burst out

Epitokes are essentially budsClues to ancestral origin of segmentationSegmentation may have been derived from incomplete budding processesPolychaete Reproduction

Phylum Annelida*Class ClitellataSubclass OligochaetaDefining characteristicsPronounced cylindrical glandular region of the body = clitellumSecond largest class in the phylum AnnelidaMost spp. are earthworms, very few are marine

Class Oligochaeta

Phylum Annelida*Polychaetes and OligochaetesOligochaetes differ from polychaetes in several ways:No parapods, fewer setae (if at all) Hermaphroditic with sex cells produced in a separate sectionNo larval stages

Oligochaete Anatomy

Oligochaete Anatomy

Seta: a.k.a. Bristles

Oligochaete Excretory System

Oligochaete Nervous System

Oligochaete Nerve Cord

Oligochaete Reproduction

Oligochaete DevelopmentFor terrestrial oligochaetes, development is direct without any larval formsSome aquatic oligochaetes retain a trochophore-like larval stage

Common Terrestrial Oligocheates: EarthwormsOctagonal-tail worm (Dendrobaena octaedra)Red marsh worm (Lumbricus rubellus)Dew-worm or nightcrawler (Lumbricus terrestris) Pink soil worm (Aporrectodea rosea)Canadian worm (Aporrectodea tuberculata)Pasture worm (Aporrectodea turgida) Woodland white worm (Octolasion tyrtaeum)Redworm (Eisenia fetida )

Quick and Easy Earthworm Morphology GuideAporrectodea turgida Lumbricus rubellus Morphology Number & location of GTs and TPs, location & shape of clitellum EcologyLocation of burrows

Aquatic Oligocheates

Hirudinea

Phylum Annelida*Leech AnatomyAnterior sucker is small and contains the mouthAnterior sucker creates a wound with saw like jawsLeeches drink other animals blood, usually vertebratesCan be carnivores, or scavengers; leeches are not set in their feeding habits

Phylum Annelida*Blood SuckerThe salivary glands excrete hirudin which prevents the blood from coagulatingMay also secrete an anaesthetic and substance to dilate small blood vesselsBlood is broken down by symbiotic bacteria that is then used by the leechesLeeches were commonly used in the 19th century for bloodletting Recent medical uses are to relieve pressure after vascular tissue is damaged Snake bites or the reattachment of a finger or ear

Phylum Annelida

Phylum Annelida*Leech ReproductionLeeches are simultaneous hermaphrodites that lack a free-living larvae stageFertilization is internal through copulation Development occurs in a cocoon similar to the Oligochaetes

*****Fig. 17.1*******Fig. 17.22**Fig. 17.2b*Fig. 17.3*Fig. 17.3d*************Fig. 17.4*Fig. 17.5*Fig. 17.10*Fig. 17.11*Fig. 21.7***Fig. 17.6**Fig. 17.12b**Fig. 17.12a*Fig. 17.12c*Fig. 17.13*Fig. 17.14*Fig. 17.15*Fig. 17.16*Fig. 17.Fig. 17*Fig. 17.18*Fig. 17.20***