Chapter 35
Section 35.1
 Means
“soft body”
 Most marine, some freshwater, a few terrestrial
 Largest marine phyla
 Diverse in size, anatomy, habitat, and behavior
 Definition:
a body cavity that is completely
lined by mesoderm and contains internal
organs
 Found in:





Molluska
Arthropoda
Echinodermata
Chordata
Annelida
 Trochophore:
larval stage of development for
aquatic mollusks and annelids

Use cilia for swimming and feeding
 Some
have a hard shell for protection
 Body
divided into 2 main section: headfoot & visceral mass:
 Head-foot:
head (mouth, sensory
structures) and foot (locomotion)
 Visceral
mass: heart & digestive,
excretion, and reproductive organs

Covered by the mantle
 Mantle:
layer of epidermis that excretes a hard
shell of calcium carbonate
 Mantle cavity: space between mantle and
visceral mass that protects the gills
 Ganglia: clustered nerve cells that control
locomotion & feeding
 Radula: flexible, tongue-like strip of tissue
covered with abrasive teeth
• radula – rasping “tongue” of chitin
1.
2.
3.
Class Gastropoda
Class Cephalopoda
Class Bivalvia
 Largest
and most diverse group of mollusks
 Most have 1 shell
 Locomotion: crawling

wavelike muscular contractions on mucus slime trail
 Can
withdraw head into mantle cavity when
threatened
 some have separate sexes,
some hermaphrodites
(Snails, slugs, nudibranchs, cowries, whelks)
Terrestrial
Marine
Fresh Water
 Hemolymph:
 Hemocoel:

circulatory fluid (clear fluid)
fluid filled spaces
A.k.a. blood cavity
tentacles- sense touch & have eyes on
ends
 respire with gills (aquatic) or exposed
blood vessels (terrestrial) by diffusion
 we eat muscular foot “escargot”

 Examples:
octopus, squid, cuttlefish,
chambered nautilus
 Marine animals, free swimming
 Meaning “head-foot”
 Foot divided into tentacles
 No shell (except chambered nautilus)

video
 Tentacles
have large suction cups
 Largest invertebrate brain
 Highly advanced eyes similar to humans
 Closed circulatory system
 Many release dark, inky fluid when alarmed
 Many have pigment cells called
chromatophores for camouflage
 video
 Separate
sexes
 Male uses tentacle to deposit sperm packet
into to the mantle cavity of female
 Internal fertilization
 Female lays mass of eggs and protects them
until they hatch

No trochophore stage
 Examples:
clams, oysters, mussels, scallops
 All have a two part shell connected by hinge
closed by adductor muscles
 aged by shell rings
 sessile
 filter feeders
 no radula
 Ganglia connected by nerve cords
 Lack a “head” region
 Live
buried in mud and sand
 Most have separate sexes
 External fertilization (except freshwater clams)
 Sealed mantle cavity (except siphons)
3
QTS./HR.
 2 SIPHONS AT POSTERIOR END
1. INCURRENT (H20, FOOD)
2. EXCURRENT (WASTE)
 DIG IN MUD <6” DEEP, SIPHONS STICK OUT
 Coelom-
body cavity containing organs
 Visceral mass- area containing digestive,
reproductive, excretory organs and heart
 Mantle- membrane encasing visceral mass;
secretes CaCo3 shell
 Also: incurrent & excurrent siphon, foot,
adductor muscles
Dorsal
Anterior
Posterior
Ventral
 ---------- /////////////
 -----------
protective outer layer
prismatic layer
pearly layer
 Most
produced by bivalves (commonly
oysters)
 CaCO3 secretion around a foreign object
He Was Shellfish
Section 35.2
 Examples:
earthworms, leeches
 Annelid means “Little rings”
 Segmentation allows for division of labor
 Bilateral symmetry
 Live in freshwater, marine water, and
terrestrial environments
 Setae:
external bristles
 Parapodia: fleshy protrusions on outside of body
 Number
of setae and parapodia divides this
phylum into three class:
Class Polychaeta
 Class Hirudinea
 Class Oligochaeta

 “Many

bristles”
Number of setae and parapodia
 Have
anetennae & specialized mouth parts
 Most are marine animals

Trochophore larvae
 Predatory
 Largest
class of annelids
 Smallest
class of annelids
 Example: leeches
 Live in calm freshwater & moist vegetation
 No setae or parapodia
 Most are carnivores & some are parasitic


Secrete anaestheic & anticlotting factors
Ingest 10 times it own weight in blood!
 “Few

bristles”
Few setae and no parapodia
 Live
in soil or freshwater
 Example: earthworms
 Divided
into over 100 segments
 Movement:





Anchor middle segments with setae
Contract muscles in front
Elongation of anterior
Setae of anterior grip ground
Pull posterior forward
 Ingest
soil as they burrow
 Digestion path: mouth  pharynx 
esophagus  crop (temp. storage)  gizzard
(releases & breaks up organic matter)  long
intestine (absorption of nutrients)  anus
Earthworm Internal Anatomy
 Closed
circulatory system
 Ventral (toward posterior) & dorsal (toward
anterior) vessels
 Aortic arches link ventral and dorsal vessels
 Respiration:
diffusion of oxygen and carbon
dioxide via moist skin

Secretion of mucus to keep moist
 Excretion:
via nephridia (excretory tubules in
every segment except first three)
 Chain
of ganglia connected by a ventral nerve
cord
 Each segment has a single ganglia
 Brain = fused ganglia
 Simple sensory skills




Light
Touch
Chemicals
temperature
 Hermaphrodites

Cannot fertilize own self
 Mating:
press ventral surfaces together, anterior
ends pointed opposite directions





Setae and mucus secreted from clitellum hold worms
together
Each worm injects sperm into mucus
Sperm enters seminal receptacles of other worm
Several days later chitin tube forms picking up eggs &
stored sperm  fertilization
Young worms develop inside tube and hatch 2-3 weeks
later
 Decomposers
of leaves and organic matter
 Recycle nutrients
 Release natural fertilizers (waste)
 Aerates the soil
 And are good for fishing
Nephridia