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Review sheet 7c (Arthropods, Echinoderms, Chordates)
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Know that phylum Arthropoda contains more animal species than any other phyla
Understand that the majority of marine arthropods are crustaceans (class Crustacea)
Know that arthropod means “jointed foot” and refers to jointed appendages such as legs and
mouthparts
Know that the body of arthropods is bilaterally-symmetric and segmented
Know that arthropods possess an external skeleton, called an exoskeleton
Know that the exoskeleton is made of chitin and must be shed regularly in order for the
arthropod to grow
Understand that crustaceans are distinct from other arthropods in having a pair (at least) of
biramous (two-part) limbs and a nauplius (naupliar) larval stage
Know that lobsters, crabs, barnacles, shrimp, copepods, krill, amphipods and isopods are all
crustaceans (class Crustacea, phylum Arthropoda)
Understand that most crustaceans possess gills in order to respire underwater
Understand that amphipods are flattened sideways and isopods are flattened dorsoventrally
Know that decapods are a group of crustaceans that have 5 pairs of appendages
Understand that because they must constantly molt (shed their exoskeleton) to grow,
arthropods have a limit on what size they can achieve
Understand that other than crustaceans, there are relatively few marine arthropods
Understand that horseshoe crabs are not crustaceans, but rather belong to subphylum
Chelicerata, and are characterized by having 6 pairs of appendages
Know that chelicerae are pointed appendages used to grasp and capture food
Know that subphylum chelicerata includes the arachnids (spiders) and so horseshoe crabs are
more closely related to spiders than to crabs and are not true crabs at all! (not decapods)
Understand that horseshoe crab blood is blue because it contains hemocyanin (not hemoglobin)
Know that sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers are members of
phylum Echinodermata
Know that Echinodermata means “spiny skin” or “hedgehog skin”
Know that phylum Echinodermata is exclusively marine (no freshwater members)
Know that adult echinoderms exhibit pentamerous symmetry, whereby the body is arranged in
5 parts around a central axis
Understand that because of the penatmeous symmetry, there is only an aboral and oral side, no
ventral, dorsal, anterior or posterior
Understand that echinoderms have an internal skeleton, or endoskeleton
Know that crinoids are echinoderms
Know the four major characteristics of phylum chordate: dorsal hollow nerve cord; notochord,
postanal tail and pharyngeal slits or gill slits
Understand that phylum Chordata includes 3 subphyla: Urochordata, Cephalochordata, and
Vertebrata
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Understand that Urochordates and Cephalochordates are invertebrate, while only Vertebrates
have a backbone
Understand that members of subphylum Urochordata exhibit all 4 characteristics of chordates
only during development (not as adults)
Understand that members of subphylum Cephalochordata exhibit all 4 characteristics of
chordates their entire lives (larvae and adult form)
Know that salps and sea squirts are Urochordates, while lancelets are Cephalochordates