4. bilaterally symmetrical worms. marine worms, and organisms hereafter, kick it up a notch...

4. Bilaterally Symmetrical Worms4. Bilaterally Symmetrical Worms


• Marine worms, and organisms Marine worms, and organisms hereafter, kick it up a notch hereafter, kick it up a notch exhibiting exhibiting bilateral symmetrybilateral symmetry (just like humans). (just like humans).

• Instead of addressing front and Instead of addressing front and back, we will discuss anterior, back, we will discuss anterior, posterior, dorsal and ventral.posterior, dorsal and ventral.

• Also pick up a CNS! Also pick up a CNS!

• Bilateral symmetry, and all Bilateral symmetry, and all that goes with it, results in that goes with it, results in enhanced motion and enhanced motion and sophisticated behaviors.sophisticated behaviors.


• AnteriorAnterior – head with brain or – head with brain or accumulation of nerve cells accumulation of nerve cells and sensory organs like eyesand sensory organs like eyes

• PosteriorPosterior – bottom/backside – bottom/backside

• DorsalDorsal – back – back

• VentralVentral – Belly – Belly

• Bilateral symmetry allows Bilateral symmetry allows organisms to actively pursue organisms to actively pursue prey and develop sophisticated prey and develop sophisticated behaviorsbehaviors

A. Flatworms: Phylum PlatyhelminthesA. Flatworms: Phylum Platyhelminthes

•Simplest flatworms – has CNSSimplest flatworms – has CNS

•Simple brain – aggregation of nerve cellsSimple brain – aggregation of nerve cells

•Several nerve cord running from brain through length of bodySeveral nerve cord running from brain through length of body

•Nervous system coordinates movement of well-developed muscular system.Nervous system coordinates movement of well-developed muscular system.


•Gut has an openingGut has an opening

•Have a middle layer of tissues, in developing embryos it is called mesodermHave a middle layer of tissues, in developing embryos it is called mesoderm

•Mesoderm gives rise to muscles, reproductive system and other organsMesoderm gives rise to muscles, reproductive system and other organs

•20,000 known species20,000 known species

•Turbellarians are the most common – striking color patternsTurbellarians are the most common – striking color patterns• Live in or on oysters, crabs, and other invertebratesLive in or on oysters, crabs, and other invertebrates


Flukes (trematodes)Flukes (trematodes)•Largest group (6,000 species)Largest group (6,000 species)•All parasiticAll parasitic

• Feed on tissues, blood, or intestinal contentsFeed on tissues, blood, or intestinal contents• Adult flukes live in vertebratesAdult flukes live in vertebrates• Larvae may inhabit invertebrates like snails and clams Larvae may inhabit invertebrates like snails and clams

or vertebrates like fish or vertebrates like fish • Larva must be eaten by a vertebrateLarva must be eaten by a vertebrate

•Common in fish, seabirds, and whalesCommon in fish, seabirds, and whales


Tapeworms (cestodes)Tapeworms (cestodes)•ParasiticParasitic

•Have long body with repeating unitsHave long body with repeating units

•Head attaches to walls of gut by suckers and Head attaches to walls of gut by suckers and hookshooks

•Lack gut or mouthLack gut or mouth

•Absorb nutrients from host across body wallAbsorb nutrients from host across body wall

•Found in invertebrates and vertebratesFound in invertebrates and vertebrates

•Longest recorded in sperm whale was 50 Longest recorded in sperm whale was 50 feet!!feet!!

B. Ribbon Worms: Phylum NemerteaB. Ribbon Worms: Phylum Nemertea

•More complex than flatwormsMore complex than flatworms

•Complete digestive tract (mouth, gut, anus)Complete digestive tract (mouth, gut, anus)

•Have a circulatory systemHave a circulatory system

•ProboscisProboscis – long flesh tube to capture prey – long flesh tube to capture prey• Everted in cavity above mouthEverted in cavity above mouth

•Feed on worms and crustaceansFeed on worms and crustaceans

•900 species, mostly marine900 species, mostly marine

•Found in all oceans, most common in shallow temperate Found in all oceans, most common in shallow temperate waterswaters

B. Ribbon Worms: Phylum NemerteaB. Ribbon Worms: Phylum Nemertea

•Some nocturnal, some brightly colored found under rocks at low tidesSome nocturnal, some brightly colored found under rocks at low tides

•Elastic, and proboscis may extend to a meter or more beyond body lengthElastic, and proboscis may extend to a meter or more beyond body length

•Longest invertebrate – reaches 100 ft!!Longest invertebrate – reaches 100 ft!!

C. Nematodes: Phylum NematodaC. Nematodes: Phylum Nematoda

• Roundworm numbers are staggering in Roundworm numbers are staggering in the marine world, yet hardly ever seenthe marine world, yet hardly ever seen

• Many are parasitic and found in most Many are parasitic and found in most marine organisms.marine organisms.

• Adapted to live in sediment or tissues Adapted to live in sediment or tissues of other organismsof other organisms


• Typically pointed at both endsTypically pointed at both ends

• Anus lies within body cavity filled with fluid that Anus lies within body cavity filled with fluid that transports nutrientstransports nutrients

• Layer of muscle in the tough but flexible body Layer of muscle in the tough but flexible body pushes and squeezes against the fluid which acts as pushes and squeezes against the fluid which acts as hydrostatic skeleton that provides support and aids hydrostatic skeleton that provides support and aids in locomotionin locomotion


• 10,000 to 25,000 species and estimates that half a million 10,000 to 25,000 species and estimates that half a million still undiscoveredstill undiscovered

• AnisakisAnisakis and few related inhabit seals and dolphins and few related inhabit seals and dolphins– Larvae found on flesh of many types of fish and may infect humans Larvae found on flesh of many types of fish and may infect humans

who eat raw or poorly cooked fishwho eat raw or poorly cooked fish

– Often larvae are vomited or coughed up without further Often larvae are vomited or coughed up without further complicationscomplications

– Sometimes penetrate into walls of stomach or intestine causing Sometimes penetrate into walls of stomach or intestine causing symptoms similar to ulcerssymptoms similar to ulcers

D. Segmented Worms (phylum Annelida)D. Segmented Worms (phylum Annelida)

• 20,000 spp. known as Annelids20,000 spp. known as Annelids

• First example of segmentation. First example of segmentation.

• Gut through all segments and lies in cavity known Gut through all segments and lies in cavity known as coelomas coelom– Coelom fluid filled and divided by partitionsCoelom fluid filled and divided by partitions

D. Segmented Worms (phylum Annelida)D. Segmented Worms (phylum Annelida)

• Segments acts as hydrostatic skeleton contracting Segments acts as hydrostatic skeleton contracting in sequence by muscles in bodyin sequence by muscles in body

• Efficient crawlers and burrowersEfficient crawlers and burrowers

i. Polychaetes (class Polychaeta)i. Polychaetes (class Polychaeta)

•Body segments of most have a pair of flattened extensions or parapodiaBody segments of most have a pair of flattened extensions or parapodia• Parapodia have stiff sharp bristles (setae)Parapodia have stiff sharp bristles (setae)

•Have closed circulatory systemHave closed circulatory system

•Muscular contractions help circulation of bloodMuscular contractions help circulation of blood

•In small organisms, oxygen in water can easily move across body wall to all In small organisms, oxygen in water can easily move across body wall to all tissuestissues

•Large organisms have gills on parapodia Large organisms have gills on parapodia • ParapodiaParapodia - - One of the fleshy paired appendages that function in

locomotion and breathing

• GillsGills - thin wall extensions of body that have capillaries where gas - thin wall extensions of body that have capillaries where gas exchange takes placeexchange takes place

Sandworm Sandworm NereisNereis


•Have planktonic larval stage – trochophoreHave planktonic larval stage – trochophore

•Biologists compare larvae stage of polychaetes with other invertebrates to Biologists compare larvae stage of polychaetes with other invertebrates to examine evolutionary relationshipsexamine evolutionary relationships

•Body 5-10cmBody 5-10cm

•Many crawl and hide under rocksMany crawl and hide under rocks

•Have several pairs of eyes and other sensory organsHave several pairs of eyes and other sensory organs

•Use proboscis with jaws to capture preyUse proboscis with jaws to capture prey

•Others are deposit feeder Others are deposit feeder


•Many live in temporary or permanent tubes made from mucus, proteins, bits Many live in temporary or permanent tubes made from mucus, proteins, bits of seaweed, cemented mud particles, sand grains, or tiny fragments of shellsof seaweed, cemented mud particles, sand grains, or tiny fragments of shells

• Tube dwelling have reduced parapodiaTube dwelling have reduced parapodia• Have tentacles which have cilia and mucus that catch organic particles Have tentacles which have cilia and mucus that catch organic particles

and move them to their mouthsand move them to their mouths• Some use feathery tentacles covered with cilia to capture, sort, and Some use feathery tentacles covered with cilia to capture, sort, and

transport particlestransport particles• Some of calcium carbonate tubes built on rocks and other surfacesSome of calcium carbonate tubes built on rocks and other surfaces

This feather-duster worm, This feather-duster worm, Sabella melanostigmaSabella melanostigma, is a perfect example, is a perfect exampleof beauty, form and function.of beauty, form and function.


•Some are ptanktonic and use flat parapodia to swimSome are ptanktonic and use flat parapodia to swim

•The Palolo worm break off & posterior half swims up to surface to spawnThe Palolo worm break off & posterior half swims up to surface to spawn• Timed with phases of the moonTimed with phases of the moon• Some places people with gather worms for foodSome places people with gather worms for food

•Live on external surface of sea stars & sea urchins, in burrows of Live on external surface of sea stars & sea urchins, in burrows of invertebrates, and shells of hermit crabsinvertebrates, and shells of hermit crabs

Beard worms (pogonophorans)Beard worms (pogonophorans)

•Highly specialized lack gut and mouthHighly specialized lack gut and mouth

•TuftTuft (thousands of long tentacles) absorb nutrients in dissolved water (thousands of long tentacles) absorb nutrients in dissolved water

•Some have symbiotic relationship w/ bacteriaSome have symbiotic relationship w/ bacteria• Bacteria use the nutrients to manufacture food for the wormBacteria use the nutrients to manufacture food for the worm

•Mostly restricted to deep waterMostly restricted to deep water

•4-7 feet4-7 feet

•Related vestimentiferans grow larger and found at hydrothermal ventsRelated vestimentiferans grow larger and found at hydrothermal vents

ii. Oligochaetes (subclass Oligochaeta)ii. Oligochaetes (subclass Oligochaeta)

•Small and found in mud and sand feeding on detritusSmall and found in mud and sand feeding on detritus

•Lack parapodiaLack parapodia

iv. Leeches (class Hirudinea)iv. Leeches (class Hirudinea)

•Blood sucking found attached to fish and other invertebratesBlood sucking found attached to fish and other invertebrates

•Distinguished by suckers and no parapodiaDistinguished by suckers and no parapodia

E. Peanut Worms (phylum Sipuncula)E. Peanut Worms (phylum Sipuncula)

•Soft unsegmented bodiesSoft unsegmented bodies

•Burrow in muddy bottoms, rocks, corals, and empty shellsBurrow in muddy bottoms, rocks, corals, and empty shells

•All are marine living in shallow watersAll are marine living in shallow waters

•Deposit feedersDeposit feeders

•Long anterior portion of body contains mouth and set of small lobes or Long anterior portion of body contains mouth and set of small lobes or branching tentaclesbranching tentacles

•Tentacles can be pulled into remaining body, become compactTentacles can be pulled into remaining body, become compact

•1-35 cm in length1-35 cm in length

F. Echiurans (phylum Echiura)F. Echiurans (phylum Echiura)

•Soft segmented sausages buried in mud or in coralSoft segmented sausages buried in mud or in coral

•Look like peanut w/out retractable spoon-like or forked proboscisLook like peanut w/out retractable spoon-like or forked proboscis

•Deposit feeders that use proboscis to gather organic matterDeposit feeders that use proboscis to gather organic matter

•Urechis caupo Urechis caupo lives in U-shaped tubes in mudlives in U-shaped tubes in mud

4. bilaterally symmetrical worms. marine worms, and organisms hereafter, kick it up a notch...

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