1. Biology Chapter 37 Mollusks and Annelids

2. I. Mollusk & Annelid Similarities Both have spiral cleavage Both have the formation of mesoderm Both have a true coelom (eucoelomate) Both have trochophore larvae (a trochophore is a larval form that have tufts of cilia at its ends and a band around the middle) – The trochophore later becomes a veliger in many free-swimming mollusks.

3. II. Phylum Mollusca “Meaning soft-bodied” Ex.’s clams, snails, oysters, squid, octopi, and chambered nautiluses

4. Phylum Mollusca Bilateral Symmetry Two main body sections – head-foot, visceral mass Complete body systems present mantle radula

5. Body Plan Have two main body regions (A head-foot and a visceral mass) A mantle covers and protects the visceral mass. It also secretes a shell. (made of calcium carbonate) The mantle cavity is a space that forms between the body and the mantle.

6. Body Plan continued… Most mollusks are bilaterally symmetrical. Therefore they have ganglia. (paired clusters of nerve cells connected by long nerve chords which extend to the body muscles and the sense organs) The feeding adaptation of mollusks is a radula. This is a tongue like strip covered by tough abrasive teeth that point backwards. (see picture on page 726)

7. B. Classification Gastropoda – stomach-footed, single shelled mollusks – Ex.’s = slugs, conches, abalones, and aquatic and terrestrial snails. – These organisms undergo a process called torsion during development. – Have an open circulatory system. Their blood called hemolymph does not remain in vessels. Instead, it is pumped through the dorsal heart and fills a cavity called the hemocoel.

8. B. Classification (continued) Bivalvia - two shelled mollusks. – Clams, oysters, scallops, and mussels. – Called bivalves because they have two shells with a hinge connecting them. Held together by adductor muscles. – Unlike gastropods, bivalves are mainly sessile as they filter feed with the use of siphons The incurrent siphon draws water over the gills The excurrent siphon sends cleaned water out of the clam

9. Bivalve Shell Layers 1. Pearly layer- the smooth, shiny layer next to the mantle. - If an grain of sand gets caught in the mantle, the pearly layer builds up around the object and forms a pearl. 2. Prismatic layer- middle layer made of calcium carbonate 3. Horny Layer- The outermost layer that looks like dried varnish.

12. 3. Cephalopoda Head-footed mollusks The foot is usually divided into tentacles Known for free-living predatory existence – ex. squid, octopi, cuttlefish, chambered nautiluses

13. Cephalopods continued…. Also known for a having a complex nervous system and a large brain. – Can process sensory info. In sophisticated ways – Even can solve simple problems and performs complex tasks such as building their own shelter from ocean debris.

14. Additional Characteristics Have a closed circulatory system Have separate sexes Contain chromatophores, giving them the ability to suddenly change colors

15. Squid 10 tentacles (the 2 longest catch the prey while the other 8 force the food into their mouth) The mantle is muscular and has the ability to pump jets of water through their body enabling them to move swiftly Most are about 1 ft. in length although the giant squid can reach a length of 60 feet and weigh as much as 3.5 tons. It is the largest known invertebrate.

16. The Octopus Octopi have only 8 tentacles More likely to catch prey on the ocean floor than squid Also about 1 foot in length, although the giant Pacific octopus can reach a size of about 8 feet.

17. III. Phylum Annelida segmented worms, marine worms, leeches

18. Phylum Annelida cont… Name means little rings and comes from the fact that the body cavity is divided into many sections or segments.

19. A. General Characteristics 2/3 of all annelids are marine, others are freshwater or terrestrial. Body is divided into segments. All major body/organ systems present in annelids. Most have bristles or setae and fleshy protrusions called parapodia.

20. B. Classes 1. Polychaeta (meaning “many bristles” – these organisms are mostly marine or found in wet sand. – ex. christmas tree worm, fireworm, and all marine worms. Fireworm Christmas tree worm

21. Polychaetes continued… Unlike other annelids they have antennae and specialized mouthparts They are also the only annelids that have the trochophore larvae They live in marine environments and free swim to feed on small animals 2/3 of all Annelids fit into this class

22. B. Classes (continued) 2. Hirundea – these organisms are external parasites. They have an anterior and posterior end and cling to animals with suckers. – ex. leeches

23. Hirundea Continued…. The smallest class of annelids (about 30 separate species) Live in fresh water Parisitize small animals and suck their blood Fact- if undisturbed, a leech can ingest 10 times their own weight in blood

24. B. Classes (continued) 3. Oligochaeta – these organisms are freshwater or terrestrial and have few bristles. – ex. earthworms

25. IV. Common Earthworm Lumbricus terrestris

26. A. General Characteristics Have approximately 100 segments. Anterior end is darker and more pointed.

27. A. General Characteristics (continued) The mouth is crescent shaped and underneath the upper lip called the prostomium. The anus is the opening at the posterior end. Both are specialized segments.

28. A. General Characteristics (continued) Segments 32-37 have a distinct swelling called the clittellum.

29. A. General Characteristics (continued) Each section except the first and the last have four pair of setae on the bottom and side to aid in locomotion.

30. B. Digestive System Takes up most of the anterior end of the body. Has no jaws or teeth, instead uses its’ muscular pharynx to suck in soil.

31. B. Digestive System (continued) Organic food particles and inorganic soil particles go through long tube-like esophagus into a round organ called the crop. The crop stores the food until it is forced through the gizzard.

32. B. Digestive System (continued) The gizzard contracts and expands causing grains of sand and food to rub together. Food is finally digested in the intestine. Intestine Food Particles

33. B. Digestive System (continued) Digested food is absorbed by the blood circulating through the intestinal wall. Wastes pass out of the anus.

34. B. Digestive System (continued) Extra Information As worms feed they loosen soil, soil would be very compacted and hard with out worms. Steps of Digestion Mouth – Pharynx - Esophagus – Crop – Gizzard – Intestine - Anus

35. C. Circulatory System Blood Flows through a set of tubes or vessels. After digestion, blood carries the products of digestion to all body cells.

36. C. Circulatory System (continued) Earthworm have no true heart. instead the have five pairs of pumping vessels called aortic arches.

37. D. Respiration and Excretion The skin is protected by a thin cuticle Thin skin enables them to absorb oxygen & give off carbon dioxide. Wastes are passed to the outside of the body through nephridia. They are a simplistic version of our kidneys.

38. E. Nervous System and Sense Organs Segment number three contains a pair of fused ganglia made up of nerve cells; function as the brain. Nerves (Ventral Nerve Chord) branch from these ganglia to control the muscles and to receive stimuli from each segment.

39. E. Nervous System and Sense Organs (continued) Earthworms have no eyes or ears but are sensitive to light and vibrations.

40. F. Muscular System have an outer and inner layer of circular muscles in the body wall. Also have longitudinal muscles. Both of these together, along with setae, are use in locomotion.

41. G. Reproductive System Are hermaphroditic but do not self-fertilize. Sperm is produces in two pair of testes and stored in sacs called seminal vesicles. A sperm duct carries the sperm to the male genital pore.

42. G. Reproductive System (continued) Eggs are produced in the ovaries and mature in the body cavity. mature eggs are carried by oviducts to the female genital pore.

43. G. Reproductive System (continued) Sperm is passed from one worm to another on the spot called the seminal receptacles. The clittellum secretes a slime ring which contains the eggs. The eggs are then in turn fertilized by the sperm.