Phylum Annelida: summary of Phylum Annelida: summary of characteristicscharacteristics

Name from Latin aName from Latin annulusnnulus meaning a ring. meaning a ring. Vermiform. Possess tissues and organs.Vermiform. Possess tissues and organs. Muscular gut with mouth and anus.Muscular gut with mouth and anus. Body divided into segments.Body divided into segments. Outer epithelium with clumps of bristles (except in forms Outer epithelium with clumps of bristles (except in forms

with suckers). May be covered with a cuticle.with suckers). May be covered with a cuticle. Body wall muscular with both circular and longitudinal Body wall muscular with both circular and longitudinal

muscles.muscles. Closed circulatory system.Closed circulatory system. Nervous system with supraoesophageal ganglion, Nervous system with supraoesophageal ganglion,

circum-oesophageal ring and ventral nerve cord.circum-oesophageal ring and ventral nerve cord. Nephridia responsible for most excretionNephridia responsible for most excretion

Phylum AnnelidaPhylum Annelida

The annelids (L. The annelids (L. annelusannelus: a little ring) are the : a little ring) are the segmented worms.segmented worms.

Annelids are coelomate, protostomes and the Annelids are coelomate, protostomes and the body is metameric being composed of serially body is metameric being composed of serially repeated segments or metameres.repeated segments or metameres.

Each segment is separate from the next Each segment is separate from the next segments being divided by partitions or septa.segments being divided by partitions or septa.

SegmentationSegmentation

Within each segment are components of Within each segment are components of most organ systems such as the most organ systems such as the circulatory, nervous and excretory circulatory, nervous and excretory systems.systems.

Thus, there is a degree of redundancy in Thus, there is a degree of redundancy in annelids so that if a segment is damaged it annelids so that if a segment is damaged it need not be fatal.need not be fatal.

SegmentationSegmentation

The evolution of segmentation is the great The evolution of segmentation is the great evolutionary innovation of the annelids.evolutionary innovation of the annelids.

Segmentation allows annelids to make Segmentation allows annelids to make more precise body movements than more precise body movements than organisms that have a hydrostatic organisms that have a hydrostatic skeleton, but lack segmentation e.g. the skeleton, but lack segmentation e.g. the pseudocoelomate nematodes.pseudocoelomate nematodes.

SegmentationSegmentation

Because the coelom is divided by septa the Because the coelom is divided by septa the force of muscle contraction in a segment is not force of muscle contraction in a segment is not transmitted throughout the body, but instead is transmitted throughout the body, but instead is confined to the single segment. confined to the single segment.

Thus, one segment may elongate while the Thus, one segment may elongate while the adjacent one contracts and this allows the adjacent one contracts and this allows the animal to make fine, controlled movements.animal to make fine, controlled movements.

MovementMovement With the exception of the leeches, the coelom is With the exception of the leeches, the coelom is

filled with fluid and acts as a hydrostatic filled with fluid and acts as a hydrostatic skeleton. skeleton.

Annelids possess circular and longitudinal Annelids possess circular and longitudinal muscles and this enables individual segment to muscles and this enables individual segment to be elongated or contracted. be elongated or contracted.

Crawling is achieved by alternating waves of Crawling is achieved by alternating waves of contraction by circular and longitudinal muscles contraction by circular and longitudinal muscles passing down the body (peristalsis).passing down the body (peristalsis).

MovementMovement

Because they have fine control of movement Because they have fine control of movement annelids have evolved a relatively sophisticated annelids have evolved a relatively sophisticated nervous system.nervous system.

Most annelids are burrowing forms and as an Most annelids are burrowing forms and as an adaptation to this lifestyle bear short chitinous adaptation to this lifestyle bear short chitinous bristles called setae on each segment. The bristles called setae on each segment. The setae enable the annelid to gain traction against setae enable the annelid to gain traction against the side of the burrow.the side of the burrow.

MovementMovement

In other annelids longer hair-like setae In other annelids longer hair-like setae assist the animal in swimming.assist the animal in swimming.

For the annelids that live in burrows or in For the annelids that live in burrows or in tubes the setae help to prevent the animal tubes the setae help to prevent the animal from being pulled out.from being pulled out.

AnnelidsAnnelids

Annelids occur worldwide being found in Annelids occur worldwide being found in the sea, freshwater, and in the soil.the sea, freshwater, and in the soil.

They feed on organic matter in the mud or They feed on organic matter in the mud or soil, by filtering suspended particles from soil, by filtering suspended particles from the water, act as predators, or suck blood.the water, act as predators, or suck blood.

AnnelidsAnnelids

The typical annelid body has a two part head The typical annelid body has a two part head made up of a made up of a prostomiumprostomium and a and a peristomiumperistomium, a , a series of segments, and a terminal series of segments, and a terminal pygidiumpygidium which contains the anus.which contains the anus.

Neither the head nor the pygidium are Neither the head nor the pygidium are considered true segments. In growth, new considered true segments. In growth, new segments form anterior to the pygidium. If an segments form anterior to the pygidium. If an annelid is cut in two the posterior segments can annelid is cut in two the posterior segments can be regrown.be regrown.

11.1

Figure 17.03a

Figure 17.03c

Annelid ClassificationAnnelid Classification

There are approximately 12,000-15,000 There are approximately 12,000-15,000 species of annelids divided into 4 classes:species of annelids divided into 4 classes: Polychaeta: polychaete wormsPolychaeta: polychaete worms Oligochaeta: earthwormsOligochaeta: earthworms Hirundinea: leechesHirundinea: leeches Siboglinidae: pogonophoransSiboglinidae: pogonophorans

Class PolychaetaClass Polychaeta

The polychaetes are the largest of the The polychaetes are the largest of the annelid classes and include more than annelid classes and include more than 10,000 described species, most of which 10,000 described species, most of which are marine. Morphologically very diverse.are marine. Morphologically very diverse.

The name “poly” “chaete” refers to the The name “poly” “chaete” refers to the numerous chaetae or bristles they numerous chaetae or bristles they possess.possess.

PolychaetesPolychaetes

Polychaetes have a well differentiated Polychaetes have a well differentiated head that has sense organs including eyes head that has sense organs including eyes and cirri (short tentacles), jaws (in and cirri (short tentacles), jaws (in predatory forms), or a fan for filter feeding.predatory forms), or a fan for filter feeding.

Most segments bear parapodia, which are Most segments bear parapodia, which are lobed structures used in swimming, lobed structures used in swimming, crawling, or for anchorage in tubes. crawling, or for anchorage in tubes. Parapodia also serve as gills. Parapodia also serve as gills.

Figure 17.03e

Figure 17.03c

Class PolychaetaClass Polychaeta Polychaetes follow one of two basic lifestyles being Polychaetes follow one of two basic lifestyles being

either sedentary/sediment burrowing (“sedentary”) or either sedentary/sediment burrowing (“sedentary”) or active hunting (“errant”) species.active hunting (“errant”) species.

Sedentary polychaetes usually exhibit variation in the Sedentary polychaetes usually exhibit variation in the structure of segments. All are filter-feeders or deposit structure of segments. All are filter-feeders or deposit feeders. feeders.

Sedentary polychaetes burrow in mud and soil or build Sedentary polychaetes burrow in mud and soil or build their own tubes from which they filter feed.their own tubes from which they filter feed.

Tubes may be made from calcium carbonate, a secreted Tubes may be made from calcium carbonate, a secreted paper-like material, or sand grains.paper-like material, or sand grains.

11.3B

Figure 17.02b

FanwormsFanworms

Most of the sedentary polychaetes, which Most of the sedentary polychaetes, which inhabit burrows or build tubes, are filter inhabit burrows or build tubes, are filter feeders and consume plankton or detritus.feeders and consume plankton or detritus.

Forms such as fanworms extend long, Forms such as fanworms extend long, modified feathery crowns of stiff prostomial modified feathery crowns of stiff prostomial tentacles to feed. Ciliary action draws in tentacles to feed. Ciliary action draws in food, which is trapped in mucus and food, which is trapped in mucus and delivered down grooves to the mouth.delivered down grooves to the mouth.

11.3A

Figure 17.02a

11.7

Figure 17.10

Burrowing polychaetesBurrowing polychaetes A number of families of sedentary polychaetes A number of families of sedentary polychaetes

burrow in soft sediments either swallowing burrow in soft sediments either swallowing sediment or scraping it of bacteria, algae, fungi sediment or scraping it of bacteria, algae, fungi and other live material. and other live material.

Many functionally resemble oligochaetes and Many functionally resemble oligochaetes and have reduced parapodia, lack prominent sense have reduced parapodia, lack prominent sense organs and have well developed circular muscles organs and have well developed circular muscles and septa.and septa.

Some have soft prehensile tentacles they use Some have soft prehensile tentacles they use collect food particles.collect food particles.

http://www.nw1design.com/clients/afen/images/pics/Polychaete.jpg

Burrowing PolychaetesBurrowing Polychaetes

Burowing polychaetes such as lugworms Burowing polychaetes such as lugworms are very common on estuaries.are very common on estuaries.

They make burrows in the sand and They make burrows in the sand and consume large quantities of sand. After consume large quantities of sand. After they’ve extracted the digestible material they’ve extracted the digestible material the remaining material is defecated and the remaining material is defecated and forms a characteristic pile outside the forms a characteristic pile outside the burrow. burrow.

Lugworm (two images above) fromhttp://marinebio.org/species.asp?id=57

Above right Lugworm casts.http://upload.wikimedia.org/wikipedia/commons/7/7b/Lugworm_cast.jpg

Burrowing PolychaetesBurrowing Polychaetes

Lugworms are an important source of food Lugworms are an important source of food for wading birds.for wading birds.

http://cache2.asset-cache.net/xc/88392324.jpg?v=1&c=IWSAsset&k=2&d=EDF6F2F4F969CEBD9BAF6D58632300DBDC286D88A6C0AC12DB7DFB94F05A5839

Predatory polychaetesPredatory polychaetes

Predatory forms of polychaetes such as Predatory forms of polychaetes such as NereisNereis have a muscular pharynx equipped have a muscular pharynx equipped with jaws that can be quickly everted to with jaws that can be quickly everted to grab prey.grab prey.

11.1

Figure 17.03a

Bobbit worm a predatory polychaete. http://www.tonywublog.com/20090319/fright-night.html  

http://weblog.greenpeace.org/defendingourmediterranean/images/180polychaete_worm_hermodice_carunculata__whole_worm_for_hibsy.jpg

Predatory polychaetesPredatory polychaetes

Predatory polychaetes typically can crawl Predatory polychaetes typically can crawl rapidly using their parapodia.rapidly using their parapodia.

They are active hunters that can sqeeze They are active hunters that can sqeeze through small spaces (e.g. in coral, through small spaces (e.g. in coral, crevices, etc.) is search of prey.crevices, etc.) is search of prey.

They consume any other invertebrates They consume any other invertebrates that they can catch and dismember.that they can catch and dismember.

11.6

Figure 17.09

Class OligochaetaClass Oligochaeta

There are over 3000 species of There are over 3000 species of oligochaetes, the most familiar of which oligochaetes, the most familiar of which are the earthworms.are the earthworms.

LumbricusLumbricus terrestris,terrestris, the common the common earthworm, grows from 4-12 inches, but earthworm, grows from 4-12 inches, but tropical forms may reach 12 feet in length.tropical forms may reach 12 feet in length.

Class OligochaetaClass Oligochaeta

Earthworms burrow in rich, damp soil and Earthworms burrow in rich, damp soil and leave their burrows at night to eat leave their burrows at night to eat vegetation and to breed.vegetation and to breed.

Earthworms play a significant role in soil Earthworms play a significant role in soil fertility by aerating the soil with their fertility by aerating the soil with their burrows, adding vegetable material, and burrows, adding vegetable material, and mixing subsoil and topsoil.mixing subsoil and topsoil.

http://www.cheshirewildlifetrust.co.uk/IMAGES/watch_earthworm.jpg

Class OligochaetaClass Oligochaeta

Darwin studied earthworms and published a book on Darwin studied earthworms and published a book on their effects on soil.their effects on soil.

He estimated that an earthworm eats its own weight in He estimated that an earthworm eats its own weight in soil daily and that in an acre of land 10-18 tons of dry soil soil daily and that in an acre of land 10-18 tons of dry soil passed through their guts annually. passed through their guts annually.

Earthworms consume dead organic material and partially Earthworms consume dead organic material and partially digest it, the waste passing out of them containing digest it, the waste passing out of them containing nutrients valuable to plants and supplemented with nutrients valuable to plants and supplemented with nitrogenous wastes from the worm.nitrogenous wastes from the worm.

Class OligochaetaClass Oligochaeta

In addition to the earthworms there are many In addition to the earthworms there are many freshwater species, most of which burrow in silt freshwater species, most of which burrow in silt and mud or creep along the bottom, although and mud or creep along the bottom, although some live among submerged vegetation. some live among submerged vegetation.

Freshwater forms usually are smaller than Freshwater forms usually are smaller than terrestrial and have more conspicuous setae. terrestrial and have more conspicuous setae.

Most respire through their skins, but some have Most respire through their skins, but some have gills. Most are algae or detritus feeders.gills. Most are algae or detritus feeders.

11.16

Figure 17.18

Freshwater oligochaetes

Class OligochaetaClass Oligochaeta

Oloigochaetes, like all annelids, have a Oloigochaetes, like all annelids, have a double circulatory system as both the double circulatory system as both the coelomic fluid and circulatory system are coelomic fluid and circulatory system are used to carry food, wastes and gases.used to carry food, wastes and gases.

The blood system is closed, with the The blood system is closed, with the dorsal blood vessel being the main dorsal blood vessel being the main pumping organ.pumping organ.

http://z.hubpages.com/u/94165_f520.jpg

Class OligochaetaClass Oligochaeta

The excretory organs are called nephridia and The excretory organs are called nephridia and there is a pair in each segment, each of which there is a pair in each segment, each of which occupies parts of two successive segments.occupies parts of two successive segments.

A ciliated funnel (the nephrostome) opens just A ciliated funnel (the nephrostome) opens just anterior of an intersegmental septum and from anterior of an intersegmental septum and from this a tubule leads into the posterior segment this a tubule leads into the posterior segment and forms a series of loops that are closely and forms a series of loops that are closely surrounded by blood vessels.surrounded by blood vessels.

Excretory organsExcretory organs

The tubule eventually opens to the outside The tubule eventually opens to the outside via an aperture called a nephridiopore.via an aperture called a nephridiopore.

The system works by cilia drawing The system works by cilia drawing coelomic fluid into the nephrostome and coelomic fluid into the nephrostome and selective reabsorbtion of salts and water selective reabsorbtion of salts and water occurs in the loops leaving only a dilute occurs in the loops leaving only a dilute urine to be excreted to the outside.urine to be excreted to the outside.

11.14

Figure 17.14

Reproduction in earthwormsReproduction in earthworms

Earthworms are hermaphroditic and mate Earthworms are hermaphroditic and mate by aligning their ventral surfaces together. by aligning their ventral surfaces together.

Each worm’s clitellum (thickened section Each worm’s clitellum (thickened section of some midbody segments) secretes of some midbody segments) secretes mucus, which holds the two worms mucus, which holds the two worms together.together.

Sperm is exchanged and stored in a Sperm is exchanged and stored in a seminal receptacle.seminal receptacle.

Reproduction in earthwormsReproduction in earthworms

After sperm has been exchanged the worms After sperm has been exchanged the worms separate and each secretes a cocoon around its separate and each secretes a cocoon around its clitelleum. The cocoon slides along the body clitelleum. The cocoon slides along the body and picks up eggs and sperm.and picks up eggs and sperm.

Fertilization occurs within the cocoon as does Fertilization occurs within the cocoon as does later embryonic development. later embryonic development.

As the cocoon slides off the worm its ends seal. As the cocoon slides off the worm its ends seal. Young worms emerge several weeks later.Young worms emerge several weeks later.

11.15

Figure 17.17

Class HirudineaClass Hirudinea

There are more than 500 species of There are more than 500 species of leeches, most of which are freshwater leeches, most of which are freshwater inhabitants.inhabitants.

Leeches have anterior and posterior Leeches have anterior and posterior suckers which they use in locomotion. suckers which they use in locomotion. With the exception of one group, leeches With the exception of one group, leeches lack septae and their coelom is largely lack septae and their coelom is largely filled with connective tissue and muscle.filled with connective tissue and muscle.

Class HirudineaClass Hirudinea

Many leeches are carnivorous, but leeches are Many leeches are carnivorous, but leeches are best known as blood-sucking ectoparasites. best known as blood-sucking ectoparasites.

The leech penetrates its host using its jaws or The leech penetrates its host using its jaws or proboscis and sucks blood with its powerful proboscis and sucks blood with its powerful pharynx. pharynx.

To ensure blood continues to flow the leech To ensure blood continues to flow the leech secretes a powerful anticoagulant (hirudin) in its secretes a powerful anticoagulant (hirudin) in its saliva.saliva.

11.18

Figure 17.20

11.17

Figure 17.19

World’s largest leechHaementeria ghilianii

Class HirudineaClass Hirudinea

For hundreds of years leeches were used For hundreds of years leeches were used for blood letting, in the belief that too much for blood letting, in the belief that too much blood caused a variety of medical blood caused a variety of medical conditionsconditions

After being discarded as a medical tool After being discarded as a medical tool leeches are again being used by leeches are again being used by surgeons.surgeons.

Class HirudineaClass Hirudinea

In reattachments of severed digits and in In reattachments of severed digits and in the case of skin grafts, because the blood the case of skin grafts, because the blood vessels are damaged, pooling of blood vessels are damaged, pooling of blood often threatens to kill the attached tissue. often threatens to kill the attached tissue.

Leeches, however, can remove the Leeches, however, can remove the pooling blood safely allowing time for veins pooling blood safely allowing time for veins to develop.to develop.

11.19

Figure 17.21

Medicinal leech feeding

Class Siboglinidae Class Siboglinidae (pogonophorans)(pogonophorans)

The pogonophorans (or beardworms) The pogonophorans (or beardworms) were formerly considered to be a phylum, were formerly considered to be a phylum, but now are considered to be derived from but now are considered to be derived from the polychaetes.the polychaetes.

These were first discovered during deep These were first discovered during deep sea dredging in 1900 off Indonesia, but sea dredging in 1900 off Indonesia, but since then about 80 species have been since then about 80 species have been identified in seas worldwide.identified in seas worldwide.

Class Siboglinidae Class Siboglinidae (pogonophorans)(pogonophorans)

While similar to tube dwelling polychaetes, While similar to tube dwelling polychaetes, the first pogonophorans were considered the first pogonophorans were considered to be a separate group because they lack to be a separate group because they lack a complete gut and appeared not to be a complete gut and appeared not to be segmented. segmented.

Class Siboglinidae Class Siboglinidae (pogonophorans)(pogonophorans)

The lack of segmentation proved to be illusory. The lack of segmentation proved to be illusory. Pogonophorans live buried in the mud and their Pogonophorans live buried in the mud and their lower ends were broken off when collected lower ends were broken off when collected during dredging.during dredging.

In 1964 complete pogonophorans were dredged In 1964 complete pogonophorans were dredged up and it was discovered that the posterior end up and it was discovered that the posterior end of pogonophorans (called the of pogonophorans (called the opisthosoma) opisthosoma) is is segmented and bears setae. segmented and bears setae.

Class Siboglinidae Class Siboglinidae (pogonophorans)(pogonophorans)

Most siboglinids live in the mud and silt of Most siboglinids live in the mud and silt of the seafloor usually at depths > 200m.the seafloor usually at depths > 200m.

The body is divided into a short forepart, The body is divided into a short forepart, which bears tentacles, a long, slender which bears tentacles, a long, slender trunk, and the small segmented trunk, and the small segmented opisthosoma. The body is covered with a opisthosoma. The body is covered with a cuticle and has setae on the trunk and cuticle and has setae on the trunk and opisthosoma.opisthosoma.

11.11

Opisthosoma

Siboglinum fiordicum

Class Siboglinidae Class Siboglinidae (pogonophorans)(pogonophorans)

Because siboglinids have no mouth or complete gut it’s Because siboglinids have no mouth or complete gut it’s unclear how they obtain nutrition.unclear how they obtain nutrition.

They absorb some nutrients in the water through their They absorb some nutrients in the water through their tentacles, but most energy apparently is derived from a tentacles, but most energy apparently is derived from a mutualistic association with chemoautotrophic bacteria. mutualistic association with chemoautotrophic bacteria.

The bacteria oxidize hydrogen sulfide to produce energy The bacteria oxidize hydrogen sulfide to produce energy and live in an expanded section of the midgut called a and live in an expanded section of the midgut called a trophosome. There is no foregut or hindgut.trophosome. There is no foregut or hindgut.

Phylum EchiuraPhylum Echiura The Echiura (from Greek -- The Echiura (from Greek -- echisechis: a viper and : a viper and uraura: a tail) are worms : a tail) are worms

that are closely related to the Annelids.that are closely related to the Annelids.

Like annelids thay have a trochophore larva, but differ from the Like annelids thay have a trochophore larva, but differ from the annelids in being unsegmented. annelids in being unsegmented.

They are widely distributed in shallow marine benthic habitats.They are widely distributed in shallow marine benthic habitats.

Possess a characteristic extensible proboscis (used in feeding on Possess a characteristic extensible proboscis (used in feeding on detritus) and a set of small hooks or spines on the tail.detritus) and a set of small hooks or spines on the tail.

Echiurans live in permanent burrows in soft sediments. Most are Echiurans live in permanent burrows in soft sediments. Most are unselective detritus feedersunselective detritus feeders

Echiura: http://www.usp.br/cbm//images/rsgallery/display/echiura02.JPG.jpg

Phylum EchiuraPhylum Echiura

Urechis caupoUrechis caupo the “innkeeper worm” is a common the “innkeeper worm” is a common inhabitant of mudflats along the coast of California. inhabitant of mudflats along the coast of California.

It builds and lives permanently in a U-shaped burrow and It builds and lives permanently in a U-shaped burrow and it uses a mucus net secreted by its proboscis to trap it uses a mucus net secreted by its proboscis to trap plankton in water it draws through its burrow.plankton in water it draws through its burrow.

UrechisUrechis is called the "innkeeper worm" because many  is called the "innkeeper worm" because many marine organisms, such as small crustaceans, marine organisms, such as small crustaceans, polychaete worms and fish, live commensally inside its polychaete worms and fish, live commensally inside its burrow. burrow.

Urechis caupo the Innkeeper wormhttp://www.ryanphotographic.com/images/JPEGS/Echiuran.jpg

Phylum SipunculaPhylum Sipuncula

The Phylum Sipuncula (from Latin: meaning The Phylum Sipuncula (from Latin: meaning “little pipe”) consists of approximately 250 “little pipe”) consists of approximately 250 species of benthic, marine worms, most from 15-species of benthic, marine worms, most from 15-30 cm in length. 30 cm in length.

Sometimes referred to as the “peanut worms” Sometimes referred to as the “peanut worms” most burrow in sand or silt or occupy crevices or most burrow in sand or silt or occupy crevices or empty mollusc shells or worm tubes.empty mollusc shells or worm tubes.

http://www.glaucus.org.uk/Sipunculus-nudus-RL.jpg

Phylum SipunculaPhylum Sipuncula

The body is unsegmented and divided into an The body is unsegmented and divided into an anterior introvert and a posterior trunk.anterior introvert and a posterior trunk.

Like the Echiurans the sipunculids are generally Like the Echiurans the sipunculids are generally non-selective deposit feeders and they use the non-selective deposit feeders and they use the tentacles surrounding the tip of the introvert to tentacles surrounding the tip of the introvert to collect food.collect food.

They produce a trochophore larva similar in They produce a trochophore larva similar in structure to that of the annelids.structure to that of the annelids.

http://www.brookscole.com/chemistry_d/templates/student_resources/0030244269_campbell/images/hottopics/Sipunculida.gif