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Mollusks, Arthropods and
Echinoderms RG
Mollusks (Ch. 35.1): Phylum _Mollusca_
snails_, _slugs_ and _octopi_ belong to this phylum,
Clams, _
soft_. Mollusks are coelomates. What does that mean and what
which means _
advantages are there to this body design?
It means they have a true body cavity and it
allows parts of their body to move
independently.
Most mollusks have a larval stage called a _trochophore_ that has cilia to
swim around with.
The body of a mollusk is divided into two parts, the _
contains sensory organs, and the _
head-foot_, which
visceral mass_, which contains the
organs for digestion, circulation, excretion and reproduction. Covering this is a layer
mantle_. Mollusks have _bilateral_ symmetry, as evidenced by
called the _
pairs of nerve clusters called _
ganglia_. Mollusks have a unique feeding feature
called a radula. Describe what it is and how it works.
“tongue” covered with “teeth” that cuts
through plants or scrapes algae
Class Gastropoda:

Means “stomach foot.” Why do you think this is an appropriate name (this isn’t
in the book, but look at how they move)?
They move around on their stomach

Includes what examples?
Snails, abalone, conch, slugs, nudibranches

torsion_ where the visceral mass turns around 180o during
Undergoes _
development.

Have an open circulatory system. What does this mean?
Hemolymph not entirely contained in vessels;
in hemocoel, “blood cavity”
 Gastropods breathe through a set of _gills_ in the mantle cavity.

Gastropods show great _
diversity_ in reproduction, some have separate
sexes_, but some are hermaphrodites.
_
Below is a picture of a gastropod. Identify the following structures:
foot
mouth
gill
heart
stomach
anus
shell
head
Class Bivalvia:

Includes what examples?
Clams, oysters, scallops

How do they get their name?
Shell has 2 halves (‘valves”)

In contrast to gastropods, most bivalves are _
most of them are _

filter_-feeders and do not have a radula.
They do not have a head or brain but have _
system. Some have rows of small _

sessile_. Because of this,
3_ pairs of ganglia for a nervous
eyes_.
Clams breathe and eat through two tubes called _
siphons_, which lead to
cilia_ on the gills circulate the water and filter out food.
a set of gills. _

Most clams have separate _
sexes_, and release the eggs and sperm into the
water to be fertilized. This is called external fertilization.
Below is a picture of a gastropod. Identify the following structures:
foot
stomach
mouth
anus
gill
shell
head-foot_)
Class Cephalopoda: (which means __

Includes what examples?
Octopi, squid, cuttlefish, nautilus

Why do think this is a good name for them?
Move head first
heart
siphon

Their nervous system is _
more_ _advanced_ than any other
invertebrate. It is divided into several _
lobes_ and has millions of nerve
cells.
eyes_ that form images.

Have complex _

Have a _

Have _

What two defenses do cephalopods have to use against predators?
closed_ circulatory system.
separate_ sexes.
Ink and chromatophores (change color)
You don’t have to label it, but
here is a picture of Cephalopod
anatomy.
Arthropods (Ch 36, Phylum: _Arthropoda_)
Arthropods are members of phylum _
Arthropoda_, which means _
jointed foot_. They are segmented animals, but have jointed extensions
_
appendages_. Support comes from an _exoskeleton_, made
called _
3_ layers. Arthropods have a high degree of _cephalization_,
up of _
including segmented antennae and compound eyes. What are these?
Many individual light detectors each with
own lens
All arthropods have open circulatory systems. What does this mean?
Heart pumps fluid into vessels that empty
into open spaces
What is molting and why do arthropods molt?
Shed exoskeleton so they can grow
Subphylum Crustacea:

Is very diverse, so only has one defining characteristic: _
2 pairs of
antannae_

Includes the following species:
Crabs, pill bugs, crayfish, lobsters, shrimp
mandibles_ to chew with

Most have a pair of “jaws” called _

Most have _

Many body segments are _

Some small ones respire through _
1 pair of_ appendages per body segment
larger ones have _

fused_ together
their exoskeleton_, while the
gills_.
They have indirect development, with a larva called a _
naupilus_.
The Crayfish (since we’ll do a crayfish dissection, we’ll use it as an example of a
crustacean)
 Is a decapod. What does this mean and why is it an appropriate name?
10 feet

it has 5 pairs of appendages
The body is divided into two parts, the _cephalothorax_ (head, first 5
segments and thorax) and the _

abdomen_ (last 6 segments).
What’s the difference (in structure and function) between antennae and
antennules?
Antennae…long, for taste & touch
Antennules…short, for taste, touch &
balance

mandibles_ to chew food and _maxillae_ and
They have _
maxilipeds_ to manipulate (move) food. These are also used in
_
respiration.
chelipeds_, ends in pincers.

The last set of walking legs, the _

The smallest legs on the abdomen are called _
swimmerets_, and are
used to create water currents and for reproduction.

Does the crayfish have a complete or incomplete digestive system? Explain.
Complete…2 openings

gills_ for respiration, located from the base of the
Crayfish have feather-like _
walking legs to beneath the carapace. When they walk, they circulate water
across their gills.

Does the crayfish have an open or closed circulatory system? Explain.
Open: heart pumps hemolymph to
regions/spaces and bathes tissues

How does the crayfish get rid of wastes?
Green glands

The nervous system consists of a pair of _
and a ventral __
ganglia_ above the esophagus
nerve cord_ that runs the length of the body.
Subphylum Chelicerata and Myriapoda

Chelicerata includes what members?
Spiders, scorpions, mites, horseshoe crabs

Most of their systems are similar to crustaceans like the crayfish. What is
unique about the way spiders respire?
Book lungs

Myriapoda includes what members?
Millipedes, centipedes

What does its name mean?
Many feet
Class Insecta (Ch 37)

Share these characteristics with other arthropods:
Segmented body
Jointed legs

The body is divided into _
exoskeleton
3_ parts. The _head_, the _thorax_ and the
abdomen_.
__

Identify the order for the following insects, the meaning of its name and their
impact on humans:
o Aphids, Cicadas: _
impact:
Homoptera_ means __like wing_,
crop and plant damage
o Termites: _
isoptera_ means _equal wing_, impact:
Decompose wood
o Dragonflies and damselflies: _
impact:
Odonata_ means _toothed_,
destroys harmful insects, nymph ios
part of food chain
Orthoptera_ means
__straight wing_, impact: damage crops and
plants
o Grasshoppers and crickets: _
Coleoptera_ means __sheathed
wing_, impact: destroy crops
Eat other bugs
o Ladybugs and beetles: _
Diptera_ means _two wings_,
impact: spread disease, pollinators, destroy
crops, decomposers
o Mosquitoes, fleas and gnats: __
o Bees, wasps and ants _
Hymenoptera_ means
membrane wing_, impact: pollinate, make
_
honey, sting, destroy other insects
o Butterflies and moths: _
Lepidoptera_ means __scaled
wing_, impact: pollinate, silk, crop/clothing
damage

Insect development. Insects go through a series of _
molts_ as they change
from egg to adult. They also undergo changes, called
metamorphosis_.
_

Label the following on the diagrams below:
o the name of the kind of metamorphosis
o the name of each stage
__complete
metamorphosis__
_incomplete
egg
metamorphosis_
egg
larva
adult
adult
nymph
pupa

In _
complete_ metamorphosis, a butterfly hatches into a worm-like
organism called a _
larva_ or caterpillar. During this stage, the organism
consumes a huge amount of food. It then spins a protective covering around
itself and the butterfly inside becomes a _
pupa_. The covering itself is called
cocoon_ or chrysalis. While inside the covering, it changes into an
a_
adult_.
_

In _
incomplete_ metamorphosis, a grasshopper egg hatches into a
nymph_. This is an immature form that looks similar to an adult, but
_
does not have _
wings_. As it grows, it _molts_, shedding its
exoskeleton and getting larger and more mature until it reaches __
adult_
stage.
Echinoderms (Ch. 38.1): Phylum _Echinodermata_
sea stars_,
This phylum, whose name means “spiny skin”, includes _
sand dollars_, _sea urchins_, and sea cucumbers. They are
_
radially_ symmetrical and do not show signs of _cephalization_.
_
They develop from larvae that are _
bilaterally_ symmetrical.
They have 4
major characteristics that are not shared by any other phylum. Explain each.

pentameral_ symmetry
_
Based on 5

endoskeleton made of _
ossicles_.
Calcium carbonate plates

water__-vascular system.
_
Not blood or hemolymph

tube_ feet.
_
Water filled
Lily-like_)
Class Crinoidea: (means _

Includes what members?
Sea lilies, feather stars
Class Ophiuroidea: (means _

snake tail_)
Includes what members?
Basket stars, brittle stars

How are they different from sea stars (starfish)?
Long, narrow arms, break off and regenerate
easily
Class Echinoidea: (means __

spine-like_)
Includes what members?
Sea urchins, sand dollars

test_.
Have a rigid endoskeleton called a _
water polyp_)
Class Holothuroidea: (means _

Includes what members?
Sea cucumbers
Class Asteroidea: (means _

star-like_)
Includes what members?
Sea stars

The two sides of sea stars are called the _
oral_ side, because it has a
mouth_ and the __aboral_ side.
_

Describe the vascular (circulatory) system of the sea star.
Water enters madreporite, into stone canal, to
arms, to tube feet

What is unique about how the sea star feeds and what does it eat?
2 stomachs…cardiac moves outside body and
takes up food, passes to pyloric

Describe the sea star’s nervous system.
Nerve ring around mouth, then a nerve down
each arm; nerve net near body surface, eye
spots at each arm.

Most sea stars (and other echinoderms) have _
pair of ovaries and testes in each _
separate_ sexes.
With a
arm_. Fertilization takes place
externally_ when eggs and sperm are shed into the water.
__

Echinoderms have remarkable powers of regeneration. Explain.
Very slow…up to a year
Regenerate arms form central part of body.
Below is a picture of a sea star. Identify the following structures:
arm
stomach
anus
tube feet
ring canal
radial canal
eye spot
oral side
aboral side
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/gastropodanatomy.gif
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/bivalveanatomy.gif
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/cephalopodanatomy.gif