Mollusca, Arthropoda and Echinodermata Review Sheet Answers:
1) Phylum, subphylum and class are:
a) Millipedes are in phylum arthropoda, subphylum uniramia and class diplipoda
b) Starfish are in phylum echinodermata (we didn’t learn the class)
c) Squid are in phylum mollusca, class cephalopoda
d) Crabs are in phylum arthropoda, subphylum crustacea.
e) Sea cucumbers are in phylum Echinodermata.
f) Clams are in phylum mollusca, class bivalvia.
g) Scorpions are in phylum arthropoda, subphylum chelicerata, class arachnida.
h) Sea urchins are in phylum Echinodermata.
i) Octopus are in phylum mollusca, class cephalopoda
j) Grasshoppers are in phylum arthropoda, subphylum uniramia, class insecta
k) Snails are in phylum mollusca, class gastropoda.
2) Functions are:
a) The respiratory system is involved in exchanging O2 and CO2 with the atmosphere.
b) The circulatory transports nutrients and sometimes O2 and CO2 to all of the cells of the body.
c) The digestive system breaks down food into its basic building blocks and absorbs the food into the blood
stream.
d) The excretory system gets rid of indigestible material and products of chemical reactions in our body
which are toxic to our body.
3) green glands are an excretory organ found in crustaceans and malpighian tubules are an excretory organ
found in land arthropods such as insects
4) Open circulatory systems are ones in which the blood is not always in blood vessels. Sometimes it will be in
haemocoels (blood sinuses). All molluscs except cephalopods (who have closed circulartory systems) have
open circulatory systems. Most arthropods also have open circulatory system.
5) Gills are found in marine arthropods and trachea and spiracles are found in terrestrial insects. Some
mollusks breather through their skin, some through gills. Echinoderms breath through their skin, and
through small “skin gills”
6) An endoskeleton is inside the animal with the muscles attached to the outside whereas exoskeletons are on
the outside of the animal and the muscle attachments are on the inside. The advantage of an endoskeleton is
that it is lighter and therefore the animal can grow to be larger. But since the animal has soft tissue on the
outside it can be injured more easily. Exoskeletons provide more protection but they are extremely heavy so
animals cannot grow as large. Animals in the ocean are able to become larger since the water will support
them but land arthropods are very small. Also, when they grow, they must shed the whole exoskeleton and
grow a new one. This takes a lot of energy and leaves them vulnerable after the shedding while they are
waiting for the exoskeleton to harden.
7) The ecological roles of :
a) Insects are involved in pollinating flowers and they are an important part of the food chain but they also
destroy crops and carry diseases.
b) Crustaceans are an important part of the food chain and fill many ecological niches in different
ecosystems.
8) Arachnids have a fused head and thorax called a cephalothorax giving them only two body segments
whereas insects have a head, thorax and abdomen. Arachnids also have 8 legs whereas insects have 6 legs.
Some of the arachnids, such as spiders have the ability to make silk whereas insects cannot.
9) Water come in through the sieve plate on the top of the sea star (or starfish) and enters the ring canal around
the central disk of the sea star. From there water travels through tubes down each arm and feed into the tube
feet of the sea star. The sea star can control how much water enters the tube feet, so it can extend, contract
and rotate them to allow for movement.
10) Phylum Mollusca all have bilateral symmetry, a “foot”, a mantle, a “shell”, no bones, a coelom, and 3 cell
layers. They all develop from a trochophore larva, and are protostomes.
11) An oyster has two shells, no head or eyes, and breathe/feeds using gills. These are the main features of class
bivlavia.
12) Gastro means “stomach” (in latin) and poda means “foot”. All the organisms in class gastropoda “walk” on
their bellies. Their “foot” is also the “stomach”.
13) Cephalopods need a closed circulatory system and two hearts because they are fast moving predators who
need to move blood efficiently through their bodies to be able to react quickly as they hunt.
14) A radula is a feeding organ common in mollusks. It is like a spike tongue that snails and slugs use to grind
away at their food.
15) For a surface to be useful for gas exchange it must be moist.
16) Chelicerae are fangs used for injecting poisons or digestive enzymes. Pedipalps are tiny little legs that work
as mouth part for handling and moving food around. Both are found on organisms in class arachnidia
(scorpions and spiders)
17) The following arthropods have antennae: subphyla crustacean, subphyla uniramia (class insect, class
diplopoda, class chilopoda)
18) A cephalothorax is a fused head/thorax common in organisms in subphyla chelicerata and crustacea.
19) A starfish eats by grabbing its prey with its arms (for example a clam) and slowly pulling it open. Then, the
starfish turns its stomach inside out into the clam, releasing a ton of digestive enzymes that slowly liquefy
the prey. Once liquefied, the starfish pulls its stomach back in, “drinking” the liquefied food with it. (yum!)