Transcript Ch. 29 PowerPoint Notes

Chapter 29
Mollusks and Annelids
Section 29.1
Mollusks
Mollusks
 Snails
 Slugs
 Oysters
 Clams
 Scallops
 Octopuses
 Squids
A True Coelem
 Mollusks and annelids are likely the first animal groups
to have true coelems
 Body Cavity
 The gut and other organs are suspended from the body wall
and cushioned by fluid
 Mollusks and Annelids
 Also contain trochophores
 Larval stage developed from fertilized eggs
Key Characteristics
 Body cavity
 True coelem
 Symmetry
 Mostly bilateral
 3-part body plan
 Visceral mass
 Central section containing the
organs
 Mantle
 heavy fold of tissue forming the
outer layer of the body
 Foot
 Muscular region used for
locomotion
 Organ systems





Excretion
Circulation
Respiration
Digestion
Reproduction
 Shell
 1 or 2 shells that serve as
exoskeleton
 Radula
 Tongue-like organ
Organ Systems
 Excretion
 Beating cilia pulls fluid from coelom
into nephridia
 Respiration
 Gills (aquatic)
 Primitive lung (terrestial)
 Recover useful molecules from
the coelomic fluid
 Reproduction
 Circulation
 3-chambered heart
 Most have male and female organs
 Snails and slugs are
hermaphrodites
Body Plans of Mollusks
 Differ in each class of mollusk
 Shell and foot are adapted to different living conditions
 Snails and slugs
Gastropods
 Single shell
 Foot for locomotion
 Terrestrial gastropods secrete
mucus from the base of their
foot
 Most are herbivores
 Some are predators

Radula may contain poison
Bivalves

Most are marine

Hinged shell (valves)

Adductor muscles connect valves

Do NOT have distinct head region or radula

Male and female

Filter feeders

Use foot to dig into sand

Siphons

Used to draw in sea water

Capable of producing pearls

Nacre
Cephalopods

Squids, octopus, cuttlefish, and nautiluses

Large head attached to tentacles
 Foot divided into many parts
 Squids have 10, octopus has 8

Nautilus has outer shell squids and cuttlefish have internal shells

Most intelligent of all invertebrates
 Well-developed brain

Draw water into mantle cavity
and expel it through a siphon
 Propulsion

Secrete fluid for protection

Active predators
 Tentacles
Section 29.2
Annelids
The First Segmented Animals
 2/3 of Annelids live in the sea
 Range in size from 1 mm to 3 meters
 Easily recognized by their segments
 Contain digestive, excretory, circulatory and locomotor organs
 Some segments are modified for reproduction, feeding or
sensation
 Cerebral ganglion
 Primitive brain
 Septa
 Internal body walls that separate segments
Characteristics of Annelids
 Coelom
 Large fluid-filled cavity
 Organ systems
 Show high degree of specialization
 The gut has different regions to perform different functions in
digestion
 Bristles
 Setae
 Found in pairs on segments of annelids
 Allow worm to crawl and anchor itself
 Parapodia
 Fleshy appendages
Annelid Groups
 Groups differ in number of setae found on each
segment
 Not all groups have parapodia
 These are the major characteristics used to classify
Annelids
Marine Worms
 Largest group of Annelids
 Iridescent colors
 Contain fleshy, paddle-like parapodia
 Many are burrowing species
 Some are free-swimming predators
Earthworms
 Contain setae on each segment
 Have no eyes
 They do have light-sensitive and touch-sensitive organs
located at the ends of their bodies
 Other sensory cells detect
moisture
 Scavengers
 Eat their way through soil
 Specialized digestive system
 Pharynx – esophagus – crop –
gizzard – intestine
Hydrostatic Skeleton
 Created by the fluid-filled coelom
 Supports each segment
 Segments become longer when circular muscles
contract
 Segments bunch up when longitudinal muscles contract
 These muscle allow them to crawl
Leeches
 Contain suckers at both ends of their body
 Most species are predators or scavengers
 Some are parasites
 Lack setae and parapodia
 Segments are not separated
internally