1. ANNELIDA
Segmented Worms

4. Phylum ANNELIDA
• means little ring Over 9K species Bilateral symmetry More advanced nervous (ganglia) and closed circulatory systems Body segmentation termed metamerism (body divided internally as well) Most have tiny bristles or setae which mainly aid in locomotion Group contains earthworms, leeches and their kin Classification: initially by setae arrangement and presence of a clitellum (packsaddle)

5. External Anatomy

6. BODY PLAN
1. usually a prostomium (lip)(mouth derived from blastophore) at 1 end and pygidium (anus) at the other 2. many septa (walls) separate segments internally 3. usually coelom serves as a hydrostatic skeleton (the use of body cavity fluids, confined by the body wall, to give support) 4. may have a fixed number of segments (leeches) 5. segments often added just before the anus tagmatization – the specialization of body regions (ex. Head – feeling sensory, thorax – locomotion, abdomen – visceral)

7. Annelids are segmented worms
Annelids are segmented worms. Their coelom is fluid-filled and serves as a hydrostatic skeleton against which muscles can pull. Septa divide the body into individual compartments. There is a closed circulatory system, ventral nerve cord, and there may be appendages on the segments.

8. Introduction to the Polychaeta the bristleworms

9. Class POLYCHAETA
• means many long hairs > 5-10cm long > largest (over 5K species) and most primitive class > mostly marine with some being bright red or green > eaten by fish, crustaceans, hydroids and others > paired appendages ( parapodia (are found beside little foot) – paired lateral extensions on each segment of polychaetes, may be used for swimming, crawling, and burrowing) but no clitellum > many crawl, burrow or live in tubes > have setae (bristles) at the ends of the parapodia > protomium – before mouth, numerous sensory organs, eyes, antenna, palps, ciliated pits and grooves, called nuchal organs > peristomium – first body segment > cuticle – protective coating    Ex: Arenicola   Amphitrite   Sabella   Chaetopterus

10. Specimen of Arenicola marina with proboscis everted. Image 17 cm

13. FEEDING straight tube
crop – storage sac
gizzard – grinding organ
RESPIRATORY
Most gases diffuse across the body wall
Closed circulatory system
Blood – colorless, red, green depends on long intestines respiratory pigment
NERVOUS & SENSORY
ganglia – nerves run dorsoventrally
…...along either side of pharynx
2-4pairs of eyes
most react negatively to increased light intensity
fanworm reacts with decreased light intensity
EXCRETE
Regulating water
Ammonia
Some across body wall
Excretory organs called Nephrida

14. REGENERATION
All polychaetes have remarkable powers of regeneration. They can replace lost parts, and some species have break points that allow worms to sever themselves when a predator grabs them. Lost segments are later regenerated.

15. REPRODUCTION & DEVELOPMENT
asexual (budding or fission) , sexual reproduction is more common Most dioecious Gametes are shed into the coelom, where they mature. Mature female worms are often packed with eggs. Gametes may exit worms by entering nephrostomes (the excretory organ of the embryo. The embryonic tube from which the kidney develops. Tubular osmoregulartory and excretory organ of many invertebrates. Functions in excretion, osmoregulation, or both) of metanephridia (an excretory organ in many invertebrates. It consists of a tubule that has one end opening at the body wall and the opposite end in the form of a funnel-like structure that opens to the body cavity) and exiting through the nephridiopore (The opening to the outside of a nephridium. An excretory opening in invertebrates), or they may be released, in some polychaetes, after the worm ruptures >Fertilization is external in most polychaetes, few species copulate >Epitoky – formation of a reproductive individual >Atoke - nonreproductive form of the species

16. CLAMWORMS Nereis clamworm
1. marine benthic " sand worms " 2. crawl out of their burrows at nite to feed 3. have about 200 segments, 4 eyes, 4 tentacles 4. swim with undulatory movements 5. seize little animals with chitinous jaws    Other polychaetes :   Scale worms Polynoe      Fireworms Hermodice    Parchment worm:   Chaetopterus a tube worm with fans

17. Clam worm (Nereis spp.)
Clam worms are free swimming, segmented worms with four pairs of tentacles and one pair of antennae. Each segment has a pair of bristly, paddle-like appendages (parapodia) that enable them to swim in the water or crawl along the seafloor. Clam worms feed on algae and other invertebrates that they find by burrowing in the sand or mud. They are food for bottom feeding fish and crabs.

18. Bearded Fireworm
gladiators

19. Parchment worm - Chaetopterus variopedatus Parchment Worm
Distribution in Britain and Ireland

20. Chaetopterus sp. Parchment worm

21. Class OLIGOCHAETA
• means few long hairs 1. earthworms have setae, lack parapodia 2. Lumbricus terrestris is the earthworm      burrow in moist rich soil      most active at nite 3. most are scavengers on leaves and animal matter 4. series of segments in the anterior half of an oligochaete is usually swollen into a girdlelike structure called clitellum, this secretes mucus during copulation and forms a cocoon. 5. food passage from the mouth > esophagus > crop > gizzard

22. Class OLIGOCHAETA
6. blood has hemoglobin and respiration is by diffusion 7. so-called brain is a pair of cerebral ganglia 8. fast escape is due to giant axons that increase conduction rate 9. sense organs include skin photoreceptors, chemoreceptors and tactile nerve endings (also a pair of setae per segment ) cuticle covers the body
11. nitrogenous wastes include ammonia and urea chloragogen tissue – similar to the vertebrate liver, it is an amino acid metabolism, it converts ammonia to urea, and excess carbs into glycogen and fat

25. EARTHWORM BEHAVIOR / REPRO.
1. must sense soil texture, acidity and calcium content 2. some learning ability (Ex: to avoid shock) 3. monoecious /segments usually mate at nite during warm moist weather 5. a tough band cocoon forms around the clitellum where fertilization occurs and hatching occurs     Freshwater Oligochaetes usually smaller but with larger setae seminal vesicles, sites for maturation and storage of sperm prior to their release

26. 7. seminal receptacles – receives sperm during copulation. 8
7. seminal receptacles – receives sperm during copulation during copulation two worms line up facing in opposite directions, with the ventral surfaces of their anterior ends in contact with each other. This orientation lines up the clitellum of one worm with the genital segments of the other worm. A mucous sheath that the clitellum secretes envelops the anterior halves of both worms and holds the worms in place. Some have penile structures, which help maintain contact between worms. The sperm duct releases sperm. Copulation lasts two to three hours, during which both worms give and receive sperm. The clitellum forms a cocoon for the deposition of eggs and sperm. The cocoon consists of mucoid and chitnous (exoskeleton) materials that encircle the clitellum. The clitellum secretes a food reserve, albumen, into the cocoon, and the worm begins to back out of the cocoon. Fertilization occurs in the cocoon. Hatching occurs in one to a few weeks freshwater oligochaetes also reproduce asexually usually by regeneration     Ex: Aeolosoma    Nais    Stylaria    Dero    Chaetogaster

27. Oligochaeta

28. Anterior end

29. Posterior end

30. Dorsal View of Anterior End

31. Ventral View of Anterior End

33. Class HIRUDINEA The Leeches
• means leech ; mostly freshwater predators 1. usually 1 to 12 inches long and any of 4 colors 2. clitellum only during the breeding season and are monoecious 3. setae replaced by suckers because they are fluid feeders and bloodsuckers 4. fixed number of somites / segments, usually 34, annuli – secondary divisions, on each true segment 5. most freshwater species are active predators or scavengers 6. freshwater species attack cattle, humans and others 7. land species feed on insect larvae, earthworms and slugs or even climb to reach birds and mammals

34. Cont.
8. the fluid feeders prefer blood and have an anticoagulant in their " saliva " to keep the flow going until they have gorged and swollen salivary glands secrete an anticoagulant called hirudin that prevents blood from clotting
10. can increase their body mass 2 – 10 times
11. gas exchange is through the body wall
12. all leeches reproduce sexually and are monoecious, none are capable of asexual reproduction or regeneration     Ex: Hirudo   Placobdella   Macrobdella