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The Animal Kingdom
Mollusks, Arthropods, and
Echinoderms
Nancy G. Morris
Volunteer State Community College
Subgrade Coelomata
Mollusks
Includes chitons, oysters, clams,
snails, slugs. octopus, squid
General Characteristics:
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molluscus = soft body
coelom greatly reduced
main cavity is hemocoel - blood-filled
cavity in open circulatory system
show no segmentation
bilateral symmetry obscure
Subgrade Coelomata
Mollusks
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Soft body composed of 3 main parts:
1) foot – large muscular, usually ventral,
locomotion
2) visceral mass
– contains digestive system,
kidneys, heart, internal organs
3) mantle – heavy folds of tissue which cover the
visceral mass; secrete shell; form siphons,
develop gill & mouth
Subgrade Coelomata
Mollusks
radula – rasping, tongue-like organ
found in all except bivalves
 trochophore larvum – freeswimming; links mollusks and
annelids to a common flatworm
ancestor

Anatomy
of
a
Clam
Phylum Mollusca Classes
Class Amphineura - chiton
 Class Bivvalvia - clams, oysters,
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mussels
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Class Cephalopoda –
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Class Gastropoda –
chambered nautilus
squid, octopus,
snails, slugs,
abalones, whelks, periwinkles, giant conch
Review: Animal
Classification
Phylum Mollusca Classes
Class Amphineura  “both nerves”
 no eyes or tentacles
 marine
 elliptical, shell of 8 plates
 chiton
Polyplacophora:
chiton
Phylum Mollusca Classes
Class Bivalvia 
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soft body between two halves
of a hinged shell
highly developed muscular foot
bilateral symmetry obscured
most marine, some fresh water
no tentacles, head, radula
 clams, oysters, scallops, mussels
Phylum Mollusca Classes
Class Bivalvia 

Pearl Production – protective
function; foreign substance gets
between mantle & shell, mantle
secretes pearly layers of nacre
around substance
clams, oysters, scallops, mussels
Phylum Mollusca Classes
Class Cephalopoda –
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“head foot”
shell reduced & internalized in
squid
no shell in octopus
largest invertebrates
possess eyes and tentacles
most active & intelligent
Phylum Mollusca Classes
Class Cephalopoda –
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most highly developed mollusk
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squid & octopus possess ink sacs which
produce melanin ; protective function
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head-foot arrangement forms a siphon
through which water can be forcibly
expelled producing “jet propulsion”
 squid, octopus, chambered nautilus
Phylum Mollusca Classes
Class Gastropoda –
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“stomach foot”
univalve – single or one-piece shell
some have no shell
largest – giant conch – 1 foot length
Urosalprix – “oyster drill” bores hole in
oyster + digests
 snails, slugs, abalones, whelks, periwinkles, giant
conch
Phylum Onychophora
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missing link between annelids and
arthropods ???
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Peripatus
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Figure 33.26 Campbell

suggests a stage in evolution of
arthropods from a segmented,
coelomate ancestor common to both
the annelids & arthropods
Phylum Onychophora
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Annelid characteristics:
–
–
–
–
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segmentally arranged nephridia
muscular body wall
ciliated reproductive tract
eye structure
Arthropod characteristics:
–
–
–
–
–
tubular heart
tracheae
hemocoel
large ganglion
mouth parts modified appendages
Subgrade Coelomata
Phylum Arthropoda
General Characteristics:
most successful and adaptable of all animals
 largest phylum in terms of numbers of species
 means “jointed foot”
 all have segmented bodies & exhibit metamerism
 suggests a common ancestry w/annelids
 segments fused into specialized regions

Subgrade Coelomata
Arthropods
General Characteristics:
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Exoskeleton of chitin – semi-rigid but
flexible; permeable to water; waxy
cuticle prevents dessication
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coelom & hemocoel
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exhibit metamorphosis (change in form)
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exhibit molting (ecdysis)
Trilobite fossil
Phylum Arthropoda Classes
Class Archnida spiders, ticks, scorpions, mites
 arthropod w/ 8 legs
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Arachnids: scorpion & mites
Phylum Arthropoda Classes
Class Crustacea 
lobsters, crayfish, shrimp, crabs
Class Chilopoda 
“100 leggers” - centipeds; 1 pr legs per
segment carnivorous; poisonous
Class Diplopoda 
“1000 leggers”- millipedes; 2 pr legs per
segment; herbivorous
Crustraceans
Diplopoda: Millipede
Anatomy of a Crayfish
Phylum Arthropoda Classes
Class Insecta 
terrestrial & aquatic insects
Class Merostomata 
horseshoe crab, king crabs;
“thigh mouth”
Insect metamorphosis
Limulus: A
living fossil
Anatomy of a Grasshopper
Subgrade Coelomata
Echinoderms (Campbell p. 625)
General Characteristics:
“spiny skin”
 all members marine
 exhibit secondary radiality
(adults radials, but ancestors &
larval forms bilateral)
 bipinnaria larvum resembles
hemichordate larvum
 nearest in relation to chordates

Subgrade Coelomata
Echinoderms
General Characteristics:
endoskeleton w/ external spines or
ossicles
 unique water vascular system for
locomotion
 body parts in 5’s or multiples of 5
 dioecious
 external fertilization
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Subgrade Coelomata
Echinoderms
General Characteristics:
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no segmentation or well defined head region
autotomy (self-amputation) survival mechanism
regeneration
no parasitic members
deutrostomes (embrylogic development
resembles chordates)
Phylum Echinodermata Classes
Class Asteroidea –
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characterized by “star”
starfish, sea stars
Class Echinoidea –
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characterized by “spines”
sea urchins, sand dollars
Class Holothuroidea –
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characterized by “whole”
sea cucumbers
Echinoderms
Sea Cucumber
Echinoderm water vascular system
bivium
trivium
madreporite
stone canal
ring canal
radial canal
ampulla
ampulacral groove
tube feet
aboral
oral
This is where you draw and label the essential
components of a starfish. The list on the left
should guide you.