7 - Molluscs.pptx

Molluscs

1. Molluscs

2. Phylum Mollusca 200,000 species More species in ocean than any other animal group Soft body enclosed by calcium carbonate shell Body covered by mantle Thin layer of tissue that secretes the shell

3. Phylum Mollusca Displays Bilateral Symmetry Ventral muscular foot used for locomotion Most had have that includes eyes and other sensory organs

4. Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.

5. Phylum Mollusca Some have radula Ribbon of small teeth used to rasp food from surfaces Made of chitin

6. Phylum Mollusca Have paired gills Portion of body may be coiled and asymetrical Occupy all marine environments – rocky shores to hydrothermal vents

7. Essentially, a mollusc is a coiled mass of vital organs wrapped in a dorsal shell.

8. Gastropods (Class Gastropoda ), or stomach foot, are the most common mollusks. Snails, limpets, abalone, and nudibranchs . 75,000 spp. nudibranch, Phidiana crassicornis Cooper’s nutmeg snail Cancellaria cooperi giant keyhole limpet Megathrua crenulata red abalone Haliotis rufescens Cone snail, Conus geographus

9. Class Gastropod – Stomach Footed Coiled mass of vital organs enclosed by a dorsal shell resting on a foot

10. Class Gastropod – Stomach Footed Most use radula to scrape algae Mud snails are deposit feeders Whelks, oyster drills, and cone shells are carnivores that prey on clams, oysters, worms, and small fishes Modified Radula to drill and rasp prey

11. Class Gastropod – Stomach Footed Nudibranchs (sea slugs) No shell Colorful branches of the gut and gills Prey on sponges and other invertebrates Produce noxious chemicals or retain undischarged nematocysts taken undigested from prey

12. Bivavles : Class Bivalvia

13. Class Bivalvia Clams, mussels, and oysters Body laterally compressed and enclosed with two parts (valves) No head or radula Gills expanded and folded used to obtain oxygen, and filter and sort food particles from water

14. Scallops also filter feed. Many have striking color patters.

15. Class Bivalvia Inner surface of shell lined w/ mantle so whole body lies in mantle cavity Strong muscles used to close valves

16. Class Bivalvia Clams burrow in sand or mud and water drawn in and out of mantle by siphons Allow clam to feed and obtain oxygen while buried

17. Class Bivalvia Mussels secrete byssal threads that attach them to rocks and other surfaces

18. Class Bivalvia Oysters cement their left shell to hard surface and other to another oyster Pearls occur when irritating particles are lodged within the mantle cavity and covered by secretions (CaCO 3 ) from oyster

19. Class Bivalvia Some scallops can swim by rapidly ejecting water from mantle cavity with siphon

20. Class Bivalvia Shipworm bores in mangroves, driftwood, and pilings Have symbiotic relationship w/ bacteria in the gut that digests wood Valves lie at the inner end of tunnel lined w/ calcium carbonate and siphon protrudes from entrance Fouling organism = settles on bottoms of boats, pilings, and other submerged surfaces

21. Cephalopods “Putting Your Head and Feet Together”

22. Class Cephalopoda (head footed) Predators specialized in locomotion Octopi, squid, and cuttlefish Agile swimmers w/ complex nervous system and reduction or loss of shell All are marine

23. Cephalopod (General Morphology) While still following the basic body plan of a mollusc , octopi are highly specialized.

24. Cephalopod (General Morphology) Large eyes on side of head Thick muscular mantle which protects head Water enters mantel and leaves through siphon = jet propulsion

25. Cephalopod: Octopi Octopi Eight long arms (2 in to 30 feet) Bottom dwellers that live in crevices, bottles, etc Have beak-like jaws and radula to rasp flesh and secrete paralyzing substance Distract predators with dark fluid from ink sac

26. Cephalopod: Squid Squid Two triangular fins on mantle – better swimmers than octopi Can remain motionless, move forward, or backward Eight arms and two tentacles, all with suckers Has pen in upper surface of mantle Few cm to 60 feet!!

27. Cephalopod: Cuttlefish Cuttlefish Eight arms and two tentacles, but body flatten w/ fin running along the body Have calcified internal shell aids in buoyancy

28. Cephalopod: Chambered Nautilus Chambered Nautilus Coiled external shell containing gas filled chambers serves as buoyancy organ Has suckerless tentacles

29. Other Molluscs Chitons (class Polyplacophora – bearer of many plates) All marine Eight overlapping shell plates covering dorsal surface Live in shallow hard bottoms Have radula to rasp algae

30. Other Molluscs Tusk shells or scaphopods (class Scaphopoda ) Elongated shell tapered at end resembling elephant tusk Sandy muddy bottoms in deep water Many species have thin tentacles to capture small prey Tusk shell hermit crab

31. Biology of Molluscs : Nervous System Gastropods and bivalves have ganglia (local brains) located in different parts of body

32. Biology of Molluscs : Nervous System Cephalopods Most complex of invertebrates Brains coordinate and store information Complex eye reflects development Octopi and cuttlefish can learn

33. Biology of Molluscs : Nervous System Cephalopods Display rapid color change coordinated with behaviors and moods, from sexual display to camouflage Cuttlefish “flash lights” while octopi change color and behavior to mimic poisonous fish and sea snakes http://www.sciencefriday.com/video/08/05/2011/where-s-the-octopus.html

34. Biology of Molluscs : Reproduction and Life History Most have separate sexes (some hermaphroditic) Bivalves, chitons , tusk snails, and some gastropods release sperm and egg into water Cephalopods and most gastropods – internal fertilization

35. Biology of Molluscs : Reproduction and Life History Cephalopods – modified arm to transfer spermatophore Develop in yolk-filled eggs attached to crevices Female dies – guarding eggs = no food Some have trochophore larvae, displaying relationship to segmented worms

36. Kings of Camouflage https://www.youtube.com/watch?v=jk9CS1Z33Qw

37. This rotation is known as torsion which is distinct from coiling and is a much more drastic change, it occurs after coiling of the visceral hump. In torsion only a narrow part of the body and the organs which pass through it are twisted, it is that small part which lies between the visceral hump and the rest of the body. Torsion changes the orientation of the mantle cavity and its organs, and the organs of the left side tend to be reduced or even lost. Torsion in Gastropoda

38. Before torsion the mantle cavity opens posteriorly, ctenidia point backwards, the auricles are behind the ventricle, the nervous system is bilaterally symmetrical, and the mouth and the anus are at opposite ends. Torsion in Gastropoda

39. After torsion the mantle cavity opens in front just behind the head, ctenidia come to lie in front and point anteriorly, the ctenidium of the right side comes to lie on the left and that of the left side on the right, the auricles become anterior to the ventricle, the auricle of the right side comes to lie on the left and vice versa, the nervous system is twisted into a figure of 8 by the crossing of the two long nerve connectives running to the viscera, and the digestive system becomes U-shaped so that the anus comes to lie in front near the mouth. Torsion in Gastropoda

40. Why is Torsion necessary?  Without torsion, withdrawal into the shell would proceed with the foot entering first and the head entering last.         - With Torsion the head enters shell first, exposing head to less predators         - In some snails a covering called an  operculum , on the dorsal, posterior margin of the foot provides protection.   (refer to "Molluscan vocabulary"). Anterior opening of the mantle cavity allows clean water to enter from the front of the snail to mantle cavity, rather then risking contamination of silt stirred up by the snail's crawling.  The twist on the mantle's sensory organs around the head is a significant advantage because it makes the snail more sensitive to stimuli coming from the direction in which it moves.