Annelids

1.

2.

Phylum Annelida
Class
Polychaeta
Class
Clitellata
Class
Aelosomata
Aelosomata
Marine worms
Subclass
Errantia
Subclass
Sedentaria
Subclass
Oligochaeta
earthworms
Subclass
Hirudinae
Leeches

3.

Class Polychaeta
• marine worms
• segmented
Class Clitellata
Subclass Oligochaeta
• earthworms
• segmented
Subclass Hirudinea
• Leeches
• segmented

4.

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.

5.

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.

6.

Metamerism (segmentation)
• Each segment is also known as a metamere
• Each metamere has a parapodia with
numerous setae
parapod
chaetae

7.

Body Cavities
Mesoderm
Eucoelomatebody cavity
completely
lined with
mesoderm
coelom
gut
Ectoderm
Endoderm

8.

Hydrostatic
Skeleton
Earthworm
Phylum Annelida

9.

Closed Versus Open
Circulatory Systems

10.

Closed Circulatory System

11.

Nervous System and Behavior
• A mass of ganglia (neural masses) forms an anterior
brain that is usually dorsal to the pharynx.
• They have either a pair of ventral nerve cords
(primitive) or a single ventral nerve cord that runs
the length of the body.
• Each segment has a swelling of the nerve cord
called a segmental ganglion.
• Sensory receptors include: chemoreceptors, touch
receptors, photoreceptors, statocysts and vibration
receptors.
• Behaviors vary depending on class/life style.

12.

Oligochaete Nervous System

13.

Digestive System
Esophagus
Gizzard
Pharynx
Crop
Buccal cavity
Mouth
Intestine

14.

Reproductive System
Seminal
vesicle
Testes
Seminal receptacle
Ovary
Sperm duct
Egg funnel
and oviduct

15.

Oligochaete Reproduction

16.

Oligochaete Excretory System

17.

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.

18.

Subclass Hirudinea

19.

Hirudo medicinalis

20.

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

21.

Class Polychaeta
Subclass Sedentaria
Fan worms,
Christmas-tree worms
Spaghetti worms
Chaetopterus
lugworms
Subclass Errantia
• Sand worms,
• Scale worms
• Fire worms
• palolo worms

22.

featherduster worms
Subclass Sedentaria

23.

Lugworm
Subclass Sedentaria

24.

Chaeopteris
Subclass Sedentaria

25.

Spaghetti worm
Lanice conchilega
Hawaii has 11 species
5 are endemic
Subclass Sedentaria

26.

Christmas tree worms
Spirobranchus giganteus
Subclass Sedentaria

27.

Scale worm
1.
Subclass Errantia

28.

Fire worm
1.
Eurythoe complanata
Subclass Errantia

29.

The pharynx is everted by contraction of body wall muscles.

30.

Parapodia- movement and respiration

31.

Polychaete Trochophore Larvae

32.

Polychaete Larvae (setiger)