1. Annelids

2. Annelids Phylum Annelida – “little ring” – segmented body
Round worm-like animal that has a long, segmented body
Sizes range from .5mm to 3m
True coelom lined with mesoderm
“tube-within-a-tube” digestive tract – mouth to anus
Segments separated by internal walls celled septa. Most segments are identical, some modified

3. Anatomy of an Earthworm
Anus
Clitellum
Circular muscle
Longitudinal muscle
Nephridia
Ganglia
Ring vessels
Reproductive organs
Ventral blood vessel
Ganglion
Brain
Mouth
Dorsal blood vessel
Crop
Gizzard
Body segments
Setae

4. Anatomy of an Earthworm

5. Feeding in Annelids Filter feeders to predators
Pharynx – very muscular, may be armed with jaws (predators and herbivores), may be sticky (mucus, detritus feeders), act like a pump (deposit feeders and parasites)
Mucus bag – filter feeders
Feather-like structures – filter feeders
Pharynx – esophagus – crop (storage) – gizzard (ground up) – intestine

6. Circulation in Annelids
Closed circulatory system – blood contained within blood vessels
Blood moves toward the head (dorsal vessel)
Blood moves away from the head (ventral vessel)
Ring vessels in each segment connect dorsal to ventral vessels
Vessels act as “hearts” which help pump blood through the system

7. Respiration in Annelids
Gills – aquatic
Skin – must stay moist, secrete cuticle (earthworm)

8. Excretion in Annelids Solid wastes pass through the anus
Waste from cellular metabolism eliminated by nephridia

9. Response in Annelids Brain and several nerve cords
Ventral nerve runs entire length of body
Sense organs most often found in polychaetes
True eyes that see shapes, Statocysts, chemical receptors, sensory tentacles, vibration sensors
Defense, runaway and hide, a few fight with jaws (sandworm)
Marine fireworms have irritating bristles

10. Movement in Annelids Muscles
Longitudinal – lengthwise – make worm longer and shorter
Circular – make worm fatter and skinnier

11. Reproduction in Annelids
Most reproduce sexually
External (broadcast) spawners – worms swarm to surface to spawn by millions
Some hermaphrodites – exchange sperm; clitellum secretes mucus ring containing eggs and sperm which forms cocoon (earthworm)

12. Groups of Annelids Three classes of Annelids Class Oligochaete
Class Polychaete
Class Hirudinea

13. Class Oligochaetes Few “bristles” – few setae
Earthworms and tubifex worms
Deposit feeders, eat dirt and produce “castings” – aerate and fertilize the soil
Tropical earthworms produce castings 18cm long and 2cm in diameter
Soil or freshwater

14. Examples of Class Oligochaetes

15. Class Polychaetes Many “bristles”
Paired, paddle-like, appendages tipped with bristles (setae) (sea mouse)
Live in all sorts of marine habitats
Some free-living, some tube-builders
May be brightly colored, iridescent, or luminescent

16. Examples of Class Polychaetes

17. Class Hirudinea Most parasitic, some carnivorous, most freshwater
6cm to 30cm long, two suckers, one at each end
Penetrate skin by use of proboscis or sharp jaws
Produce secretions that prevent clotting and anesthetizes wound
Can swallow ten times its weight

18. Examples of Class Hirudinea

19. Comparing Flatworms, Roundworms, and Annelids
CHARACTERISTIC
Shape
Segmentation
Body cavity
Digestion and excretion
Respiration
FLATWORMS
Flattened No
Acoelomate
Gastrovascular cavity with one opening only; flame cells remove metabolic wastes
Through skin; no respiratory organs
ROUNDWORMS
Cylindrical with tapering ends No
Pseudocoelomate
Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall
Through skin; no respiratory organs
ANNELIDS
Cylindrical with tapering ends
Yes
Coelomate
Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes
Through skin; aquatic annelids breathe through gills

20. Comparing Flatworms, Roundworms, and Annelids (Continued)
CHARACTERISTIC
Circulation
Response
Movement
Reproduction
FLATWORMS
No heart, blood vessels, or blood
Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli
Gliding, twisting, and turning
Sexual (hermaphrodites); asexual (fission)
ROUNDWORMS
No heart, blood vessels, or blood
Several ganglia in head region; nerve cords run length of body; several types of sense organs
Thrashing
Sexual (primary males and females)
ANNELIDS
Blood circulated through blood vessels in closed circulatory system
Well-developed nervous system with brain and several nerve cords; many sense organs
Forward peristaltic movement
Sexual (some are hermaphrodites; some have separate sexes)

21. Mollusks

22. Phylum Mollusca Phylum Mollusca 100,000 species
Most share trocophor larval stage (free-swimming larval stage)
Defined as soft-bodied animals that have an internal or external shell

23. Anatomy of a Clam Stomach Coelom Heart Shell Nephridium
Mouth
Shell
Stomach
Coelom
Heart
Nephridium
Adductor muscle
Anus
Excurrent siphon
Incurrent siphon
Gills
Mantle cavity
Foot
Intestine

24. Form and Function in Mollusks
Body Plan – four parts: mantle, foot, shell, visceral mass
Mantle – thin layer of tissue that covers most of the mollusk body – contains shell glands
Foot – movement, mouth, and associated feeding structures
Shell – protection
Visceral mass – contains all organs

25. The Mollusk Body Plan Squid Snail Shell Mantle cavity Foot Gills
Digestive tract
Clam
Early mollusk

26. Feeding in Mollusks Herbivores, carnivores, or filter feeders
Radula – found in snails and slugs – rasp-like tongue
Herbivores scrape food
Predators drill shells or “dart” food
Cephalopods – beaks
Clams, oysters, scallops – filter feeders use gills
Octopi use siphon (tube-like structure) to trap plankton

27. Respiration in Mollusks
Gills in mantle cavity in aquatic species
Modified mantle in terrestrial species

28. Circulation in Mollusks
Open circulatory system – blood flows through vessels and “sinuses” (open spaces) (clams and snails)
Closed circulatory system – blood always flows inside vessels (cephalopods)

29. Excretion in Mollusks
Remove ammonia with use of tube-shaped organs called nephridia

30. Response in Mollusks
Simple to very complex nervous systems (scallops, octopi)
Cephalopods, highly evolved eyes and brains

31. Movement in Mollusks Mucus in snails and slugs
Jet propulsion in octopi

32. Reproduction in Mollusks
In most mollusks, sexes are separate, broadcast spawners
Cephalopods, internal fertilization
Some gastropods are hermaphroditic

33. Groups of Mollusks Three classes of mollusks Class Gastropoda
Class Bivalvia
Class Cephalopoda

34. Class Gastropoda “stomach foot” Snails, slugs, abalones, nudibranchs
Some snails have operculum (hard disk on foot that forms a “door” when inside shell)
Nudibranchs feed on cnidarians; utilize nematocysts for their own defense
Bright colors mean bad taste or even poison

35. Examples of Class Gastropoda

36. Class Bivalvia “two shell” Clams, oysters, scallops Most are sessile
Epifaunal – on top of bottom (oyster, mussels)
Infaunal – in bottom (clams)
Some are motile – scallops can move by flapping shells and have eyespots (Ocelli)

37. Scallop Swimming

38. Examples of Class Bivalvia

39. Class Cephalopoda “head foot” Squid, octopus, cuttlefish, nautilus
Predators, beak for mouth
Seem to be intelligent
Move quickly via jet propulsion
Little or no shell
Highly developed eyes and brains

40. Examples of Class Cephalopoda

41. Ecology of Mollusks
Fried calamari
Shipworms
aquaculture

42. Comparing the Three Major Groups of Mollusks
MOLLUSK GROUP
Gastropods
Bivalves
Cephalopods
SHELL
Shell-less or single-shelled
Two shells held together by one or two muscles
Internal shell or no shell
FOOT
Muscular foot located on ventral side and used for movement
Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot.
Head is attached to a single foot. The foot is divided into tentacles or arms.
EXAMPLES
Snail, slug, sea hare, nudibranch
Clam, oyster, mussel, scallop
Octopus, squid, cuttlefish, nautilus