Chapter 35 Mollusks and Annelids

1. static.blogr.com www.separationsnow.com Chapter 35 Mollusks and Annelids www.math.tamu.edu www.fcps.edu

2. PhylumMolluscaThings you should know about mollusks after this chapter • Key characteristics of mollusks. • The body plan of different mollusks. • Name three classes of mollusks. • Gastropods • Bivalves • Cephalopods

3. Characteristics of Mollusks: • 2nd largest animal phylum (Arthropoda = largest) • Invertebrates such as clams, snails, slugs, squids, and octopuses. • from Latin molluscus, which means “soft. • Many have soft bodies /some have a hard shell.) • Feeding • Some are sedentary filter feeders • others are fast-moving predators. • Mollusks are true coelomates. • Trochophore larval stage • Most aquatic mollusks and annelids (NOT ALL) have this stage

4. B.Mollusk Body Plan • Divided into 2 parts: • Visceral mass • which contains the heart and the organs of digestion, excretion, and reproduction • Head-foot, which consists of: • the head, contains the mouth (including Radula- a tongue like feeding adaptation with tiny teeth that point backwards) and sensory structures • the foot, a large, muscular organ for locomotion • Coelom -limited to space around heart. • Mantle-a layer of epidermis that covers the visceral mass. (secretes the shell)

6. C.Classes • Gastropoda (snails, slugs, albalone, conch) • Bivalvia (clams, oysters, scallops) 3. Cephalopoda (octopuses, squid, cuttlefish, chambered nautiluses) www.linsdomain.com www.mcaorals.co.uk www.iptek.net.id

7. Class Gastropoda • The largest and most diverse class of mollusks • Most, including snails, abalones, and conchs, have a single shell. Slugs have no shell. • Undergo the process of torsion during larval development. • Open circulatory system in which a heart pumps hemolymph from gills or lungs into the hemocoel.

8. Class Bivalvia • Aquatic mollusks (clams, oysters, & scallops) • Shell is divided into two valves connected by a hinge. • Most are sessile filter feeders. • Bivalves lack a distinct head

9. Clams • The mantle cavity of a clam is sealed except for a pair of hollow, fleshy tubes called siphons. • Water enters through the incurrent siphon. • Water leaves through the excurrent siphon. Other Bivalves • Oysters attach to a hard surface • Scallops can move through the water by repeatedly opening their valves and snapping them shut.

10. Class Cephalopoda • Means “head-foot.” • Free-swimming predators • Have tentacles & beaklike jaws on the head. • Nervous system is very advanced. • Have a closed circulatory system. • Many use pigments to hide and disguise themselves.

11. Squids • 10 tentacles. • Propels by pumping jets of water with the mantle through an excurrent siphon. Octopuses • 8 tentacles • They often crawl along the ocean bottom or lie in wait for prey. Chambered Nautiluses • The only existing cephalopod with external shell. • Shell is coiled & divided into chambers. • The body is confined to the outermost chamber.

12. Cephalopod Intelligence • Considered the most intelligent invertebrates. • Examples: • Dexterity, tool use and manipulation. Suction cups & arms are as efficient as human’s hand. • Can learn through observation (choose colored balls) • Can “Hide” & act like sea weed, • Assess their prey. • Scientists saw octopus complete & remember mazes & patterns • Notes John Messenger, a neurobiologist at the University of Sheffield. They learn these things rather faster than a vertebrate will – like a pigeon or a rat.“ "That is quite impressive." He also points out, however, that although cephalopods learn faster at first, their skills level off. A trained octopus will always make more mistakes than a trained rodent, he says. http://en.wikipedia.org/wiki/Cephalopod_intelligence , http://www.fortunecity.com/emachines/e11/86/cephpod.html

13. Phylum AnnelidaThings you should know: • Advantages of body segmentation. • Structures used to divide annelids into three classes. • Structures in earthworms • Name 3 classes of annelids.

14. A. Characteristics of Annelids • Bilaterally symmetrical, segmented worms. (earthworms, feather-duster worms, & bloodsucking leeches. • Annelids means “little rings” (many body segments). • True coelom that is divided into separate compartments by partitions. • Most annelids have external bristles called setae • Some have fleshy protrusions called parapodia

15. Class Oligochaeta • Live in the soil or in fresh water • Have no parapodia. • Oligochaeta means “few bristles”; have a few setae on each segment. • Most familiar is the earthworm. Structure and Movement • An earthworm’s body has over 100 nearly-identical segments. • Circular and longitudinal muscles line the interior body wall. • Locomotion is made possible by segmentation.

16. Earthworms Feeding /Digestion Ingest soil as they burrow through it. • Soil is moved through these structures: • mouth • pharynx • esophagus • crop • gizzard • intestine • includes the typhlosole • anus • Earthworms play an important role in the condition of soil.

17. Closed circulatory system. • Contractions of the aortic arches and the dorsal blood vessel force blood through body vessels Respiration and Excretion • O & CO2 diffuse through moist skin, • Cellular wastes and excess water are excreted through nephridia. Neural Control • Consists of a chain of ganglia connected by a ventral nerve cord. • Sensory structures are found in all segments but are concentrated at the anterior end.

18. Reproduction • Earthworms are hermaphrodites, but an individual worm cannot fertilize its own eggs. • During mating, earthworms press their ventral surfaces together. • Held together by their setae and by a film of mucus secreted by each worm’s clitellum.

19. Class Polychaeta • Most annelids are members of the class Polychaeta, which means “many bristles.” • Polychaetes differ from other annelids in that they have antennae and specialized mouthparts. • Are the only annelids that have a trochophore stage. Class Hirudinea • Hirudinea is the smallest class, consisting of about 500 species of leeches. • Leeches have no setae or parapodia. • Many leeches are carnivores but some are parasites that suck blood from other animals.

20. Earthworm diagrams

21. Haemophagic Leeches • Attach to their hosts & remain until they become full & they fall off to digest. • Bodies are 34 segments. • Have an anterior (oral) sucker formed from the first six segments of their body, used to connect to a host for feeding and releases an anaesthetic to remain unnoticed by the host. • Use a combination of mucus and suction to stay attached and secrete an anti-clotting enzyme into the host's blood stream. • http://en.wikipedia.org/wiki/Leech • Reading assignment: page 712

22. Comparing some Mollusks & Annelids Same in both: • Both phyla are true coelomates • Most aquatic forms develop from a trochophore larvae • Some Differences: • Annelids are segmented, flexible & soft • Mollusks are not segmented but divided into 2 areas- a head/foot & a visceral mass • Many mollusks have a shell (not octopus or slug) , annelids –no shell