Annelids
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Annelids. Phylum Annelida. Class Aelosomata. Class Polychaeta. Class Clitellata. Aelosomata. Marine worms. Subclass Errantia. Subclass Sedentaria. Subclass Oligochaeta. Subclass Hirudinae. earthworms. Leeches. Annelids. Class Polychaeta marine worms segmented

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Annelids

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Annelids


Phylum Annelida

Class

Aelosomata

Class

Polychaeta

Class

Clitellata

Aelosomata

Marine worms

Subclass Errantia

Subclass Sedentaria

Subclass

Oligochaeta

Subclass

Hirudinae

earthworms

Leeches


Annelids

  • Class Polychaeta

    • marine worms

    • segmented

  • Class Clitellata

  • Subclass Oligochaeta

    • earthworms

    • segmented

  • Subclass Hirudinea

    • Leeches

    • segmented


Characteristics

  • Segmentation (metameric body plan)

  • Eucoelomate

  • 15,000 species

  • Closed circulatory system, but no heart

  • Hydrostatic skeleton

  • Excretion- protonephridia, metanephridia, diffusion or gills

  • Simple gut

  • Respiration- diffusion or gills

  • Central nervous system- brain and nerve cord

  • Reproduction- asexual or sexual (many gonochoric)

  • Sensory system of tactile organs, taste buds, statocysts,photoreceptor cells, and eyes with lenses.


Subclass Oligochaeta

  • Lack parapodia and have few setae

  • Lack the distinctive head region of polychaetes and have no eyes.

  • Scavengers that consume soil that contains organic matter

  • The ingested soil moves into a storage chamber called the crop, then to an area called the gizzard, where grinding action breaks down the soil particles. Undigested material passes out the anus in a form called castings, which are prized as soil fertilizer.


Metamerism (segmentation)

  • Each segment is also known as a metamere

  • Each metamere has a parapodia with numerous setae

parapod

chaetae


gut

Body Cavities

Mesoderm

coelom

Eucoelomate- body cavity completely lined with mesoderm

Ectoderm

Endoderm


Hydrostatic Skeleton

EarthwormPhylum Annelida


Closed Versus Open Circulatory Systems


Closed Circulatory System


  • Nervous System and Behavior

  • A mass of ganglia (neural masses) forms an anterior brain that is usually dorsal to thepharynx.

  • They have either a pair of ventral nerve cords(primitive) or a single ventral nerve cord that runsthe length of the body.

  • Each segment has a swelling of the nerve cord called a segmental ganglion.

  • Sensory receptors include: chemoreceptors, touchreceptors, photoreceptors, statocysts and vibration receptors.

  • Behaviors vary depending on class/life style.


Oligochaete Nervous System


Digestive System

Esophagus

Gizzard

Pharynx

Crop

Buccal cavity

Intestine

Mouth


Reproductive System

Seminal

vesicle

Ovary

Testes

Egg funnel

and oviduct

Sperm duct

Seminal receptacle


Oligochaete Reproduction


Oligochaete Excretory System


Subclass Hirudinea

  • Leeches

  • Most live in fresh bodies of water, but some live among moist vegetation.

  • Suckers found on both ends

  • Unlike other annelids, its segments are not separated internally

  • Leeches lack both setae and parapodia

  • Most are predators or scavengers. Very few are parasites.

  • They secrete anticoagulants, hirudin, to keep blood from clotting and anesthetic that prevents the host from feeling their presence.


Subclass Hirudinea


Hirudo medicinalis


Class Polychaeta

  • Largest group of annelids

  • Primarily marine

  • Most segments include a pair of paddle–like parapodia

  • Well-developed head with eyes and other sensory structures


Class Polychaeta

Subclass Sedentaria

  • Fan worms,

  • Christmas-tree worms

  • Spaghetti worms

  • Chaetopterus

  • lugworms

  • Subclass Errantia

  • Sand worms,

  • Scale worms

  • Fire worms

  • palolo worms


featherduster worms

Subclass Sedentaria


Lugworm

Subclass Sedentaria


Chaeopteris

Subclass Sedentaria


Spaghetti worm

Lanice conchilega

  • Hawaii has 11 species

  • 5 are endemic

Subclass Sedentaria


Christmas tree worms

Spirobranchus giganteus

Subclass Sedentaria


Scale worm

Subclass Errantia


Fire worm

Eurythoe complanata

Subclass Errantia


The pharynx is everted by contraction of body wall muscles.


Parapodia- movement and respiration


Polychaete Trochophore Larvae


Polychaete Larvae (setiger)


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