1. Marine Annelids the Polychaetes
Lecture 4
Marine Annelids
the Polychaetes

2. polychaeta General characters
(pol'e-ke'ta) (Gr. polys, many, + chaiti?, long hair).
About 5300 species.
Segmented inside and out; parapodia used in locomotion with many large number of chitinous bristles setae
Distinct head with eyes, palps, and tentacles
No clitellum
Separate sexes
Trochophore larva usually present
Mostly marine.
Examples: Nereis
Jaws
Teeth
Postomial tentachels
Peristomial palps
Peristomial tentachels

3. Introduction marine worms of polychaeta
Almost all marine annelids are polychaetes (class Polychaeta), which are also known as “bristle worms” for their stiff and often sharp bristles stemming from each of their repeated segments
Bristles replaced by gills in many species
Planktonic larvae stage; named?????
Most free-living (living in substrate or free-swimming), but some live in mucus-supported tubes that are surrounded by substrate
Many are active predators, while others are filter feeders

4. Habitat Many crawl on or burrow in the seafloor.
A few drift and swim in the plankton.
Polychaetes include carnivores, scavengers, and planktivores.
Tube-dwelling polychaetes are suspension feeders, using feathery tentacles to trap and capture suspended material
The brightly colored fanworms trap planktonon by feathery tentacles.

5. External features
Hyperlink to external features..\..\Documents\Nereis, polychaete clamworm.mp4

6. Parapodium

7. Body wall
It consists of an outer cuticle which is secreted by The cells of the hypodermis just beneath it .
Several muscular layers under the hypodermis (could you mention these muscles?
The coelom (cavity between …….and ……..), it is divided into chambers by segments septa which is perforated beneath the intestine to allow the fluid to pass between chambers.

8. Polychaeta systems Nervous System Digestive system Circulatory System
Respiratory system
Excretory System
Reproduction

9. Nervous System
dorsal brain: (brain is fond above the pharynx in the head which is consists of a pair of supra-pharyngeal ganglia that connected with a pair of sub pharyngeal ganglia by acircum pharyngeal commissure on either side which from a ring around the pharynx) .
Ventral nerve cord with a pair of ganglia in each segment.
The brain gives off:-
A- An optic nerve to each eye
B- Palpal nerve to each palp
C- Atentacular nerve to each group of tentacles.
Three pairs of nerves arise from each of ganglia of the ventral nerve chain
- One pair to A- the parapodia
B- the anterior of the segment
C- the muscles of the segment

10. Nervous System

11. Digestive system
The mouth opens into the pharynx which forms assort of proboscis which is accomplished by protractor and retractor muscles this enable the muscular pharynx to everted through the mouth.
The pharynx leads into a slender esophagus which have digestive gland .
Straight stomach (intestine) following the esophagus it extending to the anus .

12. Feeding
Clamworms (Nereis) crawl about on marine surfaces hunting for food using well-developed sensory structures. Once located, prey are seized with chitinous jaws on a rapidly everted, muscular pharynx
..\..\Documents\Polychaete worm.mp4
..\..\Documents\Nereis virens feeding.mp4
Larval polychaete feeds on algae!!!!!!

13. Circulatory System
The blood is contained in contractile tube ( the blood vessels ).
There is a dorsal vessel , that lies between the two dorsal longitudinal muscles bands ( which carried blood anteriorly ).
A ventral vessel below the intestine which carries blood posteriorly.
In each segment , the longitudinal vessels are connected on either side by right and left transverse vessels to
form networks of capillaries in parapodia.

14. Respiratory system
Although many of the smaller polychaetes lack respiratory structures, the larger one possess gills (the parapodia)
Gills are usually modifications of the parapodia

15. Excretory System
Every segment contains a pair of nephridia except the peristomium and the anal segment .
Each nephridium opens into the coelomic cavity by means of a ciliated funnel.
Each nephridium passes posteriorly through the septum into the following segment. Where it forms coiled tube .
It opens at the base of aparapodium on the ventral surface through nephridiopore.

16. Reproductive system and reproduction
Sexes are separate. 
No well defined gonads are present but during breeding season ova or spermatozoa arise from the wall of the coelom in each segment except near the anterior end.
At this time the worm is differentiated into 2 regions:
An anterior atoke.
A posterior epitoke which contains the gonads
The specialized worm is called aheteronereid.
(Could you summarize the morphological changes that takes place in heteroneries?
Fertilization occurs (external ) in the open water.
Trochophore larvae develop from the fertilized eggs.
..\..\Documents\Spawoing Sandworms (Nereis virens) with Tidepool Tim of Gulf of Maine, Inc..flv