Chapter 33

Which of the following is characteristic of the phylum Platyhelminthes?

They are dorsoventrally flattened. This is why they are also called flatworms.

Which of the following is true of annelids?

They perform gas exchange across their skin. Cutaneous respiration occurs across their skins. Polychaetes have lateral extensions, called parapodia, which provide even more surface area for cutaneous respiration.

Which of the following is a hypothesis the researchers were testing in this study?

Through evolution, periwinkle populations with a history of predation by crabs have become less vulnerable to crab predation. The researchers' hypothesis was that southern periwinkle populations with a history of predation by crabs have become less vulnerable to crab predation through evolution.

Members of the phylum Mollusca _____.

are soft-bodied and often covered by a shell

The animal phylum most like the protists that gave rise to the animal kingdom is _____.

Proifera Evidence that supports this includes the lack of true tissue in sponges and the close similarity between choanocytes and choanoflagellates.

Which of the following are thought to be most closely related to humans? See Concept 33.5 (Page 711)

Sea Stars; Humans and sea stars are deuterostomes.

What evidence suggests that vertebrates are more closely related to echinoderms than are any other invertebrate phyla?

Shared DNA sequences; The clade Deuterostomia comprising chordates (including vertebrates) and echinoderms is defined primarily by DNA similarities. Read about deuterostomes. Return to Assignment

Based on the results shown in the graph, how has natural selection affected populations of flat periwinkles in the southern Gulf of Maine over the last century?

Southern populations of flat periwinkles have accumulated traits that make them less vulnerable than northern populations to predation by European green crabs.

Which of the following are thought to be most closely related to humans? Which of the following are thought to be most closely related to humans? sea stars ants snails earthworms jellies

sea stars Humans and sea stars are deuterostomes.

Why did the researchers set up four treatments?

to test whether the origin (northern site or southern site) of the crabs and periwinkles affected their interactions

Which of the following is an independent variable in this experiment?

the source of the periwinkles (northern or southern sites in the Gulf of Maine); One of the independent variables was the source of the periwinkle population--northern or southern sites in the Gulf of Maine. The source of the crab population was also an independent variable.

Why did the researchers present unshelled northern and southern periwinkles to northern and southern crabs in the second experiment?

to test if either population of periwinkles was unpalatable to either population of crabs; The researchers wanted to rule out the possibility that northern crabs didn't like the taste of southern periwinkles or that southern crabs didn't like the taste of northern periwinkles. This experiment allowed researchers to conclude that differences in numbers of southern and northern periwinkles killed were due to differing vulnerability to crab predation, not due to crab preferences.

Nematodes and arthropods are the largest ecdysozoan phyla. Which of the following statements are true?

Arthropods are named for their jointed appendages. Both nematodes and arthropods must molt in order to increase in size. Both nematodes and arthropods possess an external covering, or cuticle. Some nematodes are parasitic on humans. Arthropods possess an open circulatory system. (The ecdysozoans include nematodes, arthropods, and other phyla that have tough external coats, or cuticles, that must be shed as they grow. This process of shedding, or molting, is called ecdysis. Nematodes, or roundworms, are unsegmented pseudocoelomate worms that lack a circulatory system. Although most nematodes are free-living, some well-known nematodes, such as hookworms and pinworms, are parasitic.)

The phylum Arthropoda includes four major lineages: cheliceriforms (also called chelicerates); myriapods; insects and their relatives (together called hexapods); and crustaceans.

Chelicaeriforms: Arachnids, Horseshoe Crab, Possess Clawlike Feeding Appendages Myriapods: Millipedes and Centipedes, Exclusively Terrestrial Insects: Butterfly, Wings allow Flight, Body divided into Head, Thorax, and Abdomen, Three pairs of walking legs Crustaceans: Primarily Aquatic, Crabs and Isopods, Two pairs of Antennae Cheliceriforms, which are named for their clawlike feeding appendages, called chelicerae, include sea spiders, horseshoe crabs, spiders, scorpions, ticks, and mites. Myriapods include millipedes and centipedes, which are terrestrial species. Crustaceans are primarily aquatic animals such as lobsters, crabs, and crayfish. Insects possess three body regions (head, thorax, and abdomen), may have one or more pairs of wings, and have six legs. Insects are the largest and most diverse group of arthropods, including numerous species of butterflies, beetles, flies, ants, and many others.

- Differentiating between arthropods The phylum Arthropoda includes four major lineages: cheliceriforms (also called chelicerates); myriapods; insects and their relatives (together called hexapods); and crustaceans. What defines them?

Cheliceriforms, which are named for their clawlike feeding appendages, called chelicerae, include sea spiders, horseshoe crabs, spiders, scorpions, ticks, and mites. Myriapods include millipedes and centipedes, which are terrestrial species. Crustaceans are primarily aquatic animals such as lobsters, crabs, and crayfish. Insects possess three body regions (head, thorax, and abdomen), may have one or more pairs of wings, and have six legs. Insects are the largest and most diverse group of arthropods, including numerous species of butterflies, beetles, flies, ants, and many others.

In Figure 33.2 in your textbook, which two main clades branch from the most recent common ancestor of the eumetazoans?

Cnidaria and Bilateria

Insects are the most diverse group of organisms, in terms of numbers of species, dominating terrestrial habitats. More than 30 orders of insects have been described, with the order Coleoptera being the largest. Classification is based on traits such as wings and mouthparts. All insects have a three-part body plan consisting of a head, thorax, and abdomen; three pairs of walking legs; and one or two pairs of wings. The chart below indicates defining characteristics for eight of the more than 30 orders of insects. Complete the chart by following these steps: Drag blue labels onto blue targets only to identify wing characteristics. Drag white labels onto white targets only to identify the type of development. Drag pink labels onto pink targets only to identify examples of insects in each order.

Coleoptera: Hard forewings protect membranous hindwings, Complete metamorphosis, Beetles Diptera: Hindwings reduced to stabilizers, Complete metamorphosis, Flies Hemiptera: Thick forewings (except at tips), Incomplete metamorphosis, "True Bugs" Hymenoptera: Membranous forewings and hindwings, Complete metamorphosis, Ants, Bees, Wasps Lepidoptera: Wings have scales, Complete metamorphosis, Butterflies, Moths Orthoptera: One pair leathery, one pair membranous, Incomplete metamorphosis, Grasshopper, crickets Trichoptera: Hairy wings, Complete metamorphosis, Caddisflies Insects and their relatives are the most species-rich group of living organisms. The diversity of characteristics such as wing shape, mouthparts, and reproductive tactics enable insects to live in most terrestrial and freshwater habitats. The evolutionary tree below shows the relationship between the phyla and subphyla within the clade Ecdysozoa, which includes animals with tough outer coverings that must be shed for growth to occur. Myriapods, cheliceriforms, crustaceans, and insects and their relatives (hexapods) together comprise the phylum Arthropoda, which is marked by jointed appendages, segmented bodies, and hard exoskeletons. Note that the tree does not show all phyla in the clade Ecdysozoa, nor does it show all orders of insects and their relatives in the subphylum Hexapoda https://session.masteringbiology.com/problemAsset/1104618/26/1104618_025.jpg

Which of the following best summarizes the results shown in the graph?

Crabs are more successful in preying on northern periwinkles.

How was repeatability demonstrated in this experiment?

For each treatment, 12-14 crabs were offered a selection of periwinkles.

Which of the following combinations of phylum and description is incorrect?

Porifera-gastrovascular cavity, coelom present

A marine biologist dredges up a small animal from the bottom of the ocean. It is uniformly segmented, with short, stiff appendages and soft, flexible skin. It has a complete digestive system and a closed circulatory system, plus multiple true coeloms. Based on this, you determine that the animal must be a(n) _____.

annelid; The description matches the characteristics of annelids.

Which of the following is a characteristic of cnidarians?

gastrovascular cavity The gastrovascular cavity, characterized by a single opening, is the digestive compartment of cnidarians.