Chapter 33 - An Introduction to Invertebrates

Question 1

Invertebrates -

Answer 1

are animals that lack a backbone

Question 2

Phylum Porifera -

Answer 2

Animals in the phylum Porifera are known informally as sponges

Question 3

Filter feeders -

Answer 3

filter out food particles suspended in the surrounding water as they draw it through their body

Question 4

The spongocoel -

Answer 4

water is drawn through the pores into a central cavity

Question 5

The Osculum

Answer 5

where water flows out of the sponge through a larger opening

Question 6

tissues

Answer 6

groups of similar cells that act as a functional unit as in muscle tissue and nervous tissue.

Question 7

Choanocytes

Answer 7

lining the interior of the spongocoel are flagellated choanocytes, or collar cells (named for the finger-like projections that form a “collar” around the flagellum). These cells engulf bacteria and other food particles by phagocytosis

Question 8

Mesohyl

Answer 8

gelatinous region separating the body of a sponge consisting in two layers of cells

Question 9

amoebocytes

Answer 9

named for their use of pseudopodia. These cells move through the mesohyl and have many functions. For example, they take up food from the surrounding water and from choanocytes, digest it, and carry nutrients to other cells. Amoebocytes also manufacture tough skeletal fibers within the mesohyl.

Question 10

totipotent

Answer 10

capable of becoming other types of sponge cells

Question 11

Hermaphrodites -

Answer 11

meaning that each individual functions as both male and female in sexual reproduction by producing sperm and eggs

Question 12

Sequential hermaphroditism -

Answer 12

They function first as one sex and then as the other

Question 13

eumetazoans (“true animals”)

Answer 13

members of a clade of animals with tissues

Question 14

Cnidarians -

Answer 14

diversified into a wide range of sessile and motile forms, including hydras, corals, and jellies (commonly called “jellyfish”). Yet most cnidarians still exhibit the relatively simple, diploblastic, radial body plan that existed in early members of the group some 560 million years ago

Question 15

the gastrovascular cavity -

Answer 15

a central digestive compartment with a single opening to this cavity functions as both mouth and anus

Question 16

Polyps

Answer 16

cylindrical forms that adhere to the substrate by the aboral end of their body (the end opposite the mouth) and extend their tentacles, waiting for prey

Question 17

A medusa (plural, medusae) -

Answer 17

resembles a flattened, mouth-down version of the polyp. It moves freely in the water by a combination of passive drifting and contractions of its bell-shaped body. Medusae include free-swimming jellies

Question 18

cnidocytes

Answer 18

cells unique to cnidarians that function in defense and prey capture. Cnidocytes contain cnidae (from the Greek cnide, nettle), capsule-like organelles that are capable of exploding outward and that give phylum Cnidaria its name

Question 19

nematocysts

Answer 19

contain a stinging thread that can penetrate the body surface of the cnidarian’s prey

Question 20

noncentralized nerve net

Answer 20

Cnidarians have no brain. Instead, movements are coordinated by a noncentralized nerve net that is associated with sensory structures distributed around the body. Thus, even though it lacks a brain, the animal can detect and respond to stimuli from all directions.

Question 21

Medusozoa -

Answer 21

All cnidarians that produce a medusa are members of clade Medusozoa, a group that includes the scyphozoans (jellies) and cubozoans (box jellies) shown in Figure 33.6a, along with the hydrozoans. Most hydrozoans alternate between the polyp and medusa forms,

Question 22

Anthozoa

Answer 22

Sea anemones and corals belong to the clade Anthozoa. These cnidarians occur only as polyps

Question 23

exoskeleton

Answer 23

external skeleton of calcium carbonate

Question 24

Bilateria

Answer 24

whose members exhibit bilateral symmetry and are triploblastic. Most bilaterians also have a digestive tract with two openings (a mouth and an anus) and a body cavity

Question 25

lophotrochozoans

Answer 25

unique morphological features are widely shared within the group—in fact, the lophotrochozoans are the most diverse bilaterian clade in terms of body plan. This diversity in form is reflected in the number of phyla classified in the group: Lophotrochozoa includes 18 phyla, more than twice the number in any other clade of bilaterians.

Question 26

Flatworms

Answer 26

(phylum Platyhelminthes) live in marine, freshwater, and damp terrestrial habitats. In addition to free-living species, flatworms include many parasitic species, such as flukes and tapeworms.

Question 27

triploblastic

Answer 27

lack a body cavity. Their flat shape increases their surface area, placing all their cells close to water in the surrounding environment or in their gut. Because of this proximity to water, gas exchange and the elimination of nitrogenous waste (ammonia) can occur by diffusion across the body surface.

Question 28

protonephridia -

Answer 28

networks of tubules with ciliated structures called flame bulbs that pull fluid through branched ducts opening to the outside

Question 29

planarians

Answer 29

abundant in unpolluted ponds and streams, planarians prey on smaller animals or feed on dead animals. They move by using cilia on their ventral surface, gliding along a film of mucus they secrete. Some other rhabditophorans also use their muscles to swim through water with an undulating motion. features a pair of light-sensitive eyespots as well as lateral flaps that function mainly to detect specific chemicals

Question 30

Syndermata

Answer 30

the rotifers (former phylum Rotifera) and the acanthocephalans (former phylum Acanthocephala), should be combined into a single phylum

Question 31

rotifers

Answer 31

have an alimentary canal, a digestive tube with two openings, a mouth and an anus. Internal organs lie within the hemocoel (see Figure 32.9b). Fluid in the hemocoel serves as a hydrostatic skeleton. Movement of a rotifer’s body distributes the fluid throughout the body, circulating nutrients.

Question 32

parthenogenesis

Answer 32

Some species consist only of females that produce more females from unfertilized eggs, a type of asexual reproduction

Question 33

acanthocephalans

Answer 33

a group of highly modified “rotifers.” All acanthocephalans are parasites that have complex life cycles with two or more hosts

Question 34

Ectoprocta and Brachiopoda

Answer 34

Bilaterians in the phyla Ectoprocta and Brachiopoda have a lophophore, a crown of ciliated tentacles around their mouth (see Figure 32.12a). As the cilia draw water toward the mouth, the tentacles trap suspended food particles. Other similarities, such as a U-shaped alimentary canal and the absence of a distinct head, reflect these organisms’ sessile existence

Question 35

Ectoprocts

Answer 35

are colonial animals that superficially resemble clumps of moss. (In fact, their common name, bryozoans, means “moss animals.”) In most species, the colony is encased in a hard exoskeleton studded with pores through which the lophophores extend

Question 36

Brachiopods -

Answer 36

superficially resemble clams and other hinge-shelled molluscs, but the two halves of the brachiopod shell are dorsal and ventral rather than lateral, as in clams. All brachiopods are marine. Most live attached to the seafloor by a stalk, opening their shell slightly to allow water to flow through the lophophore

Question 37

molluscs

Answer 37

molluscs are marine, roughly 8,000 species inhabit fresh water, and 28,000 species of snails and slugs live on land. All molluscs are soft-bodied, and most secrete a hard protective shell made of calcium carbonate.

Question 38

foot

Answer 38

a muscular foot, usually used for movement

Question 39

a visceral mass

Answer 39

containing most of the internal organs

Question 40

a mantle

Answer 40

a fold of tissue that drapes over the visceral mass and secretes a shell (if one is present)

Question 41

the mantle cavity

Answer 41

a water-filled chamber, which houses the gills, anus, and excretory pores

Question 42

a radula

Answer 42

a straplike organ used to feed as it scrapes up food

Question 43

Polyplacophora

Answer 43

chitons, Chitons have an oval-shaped body and a shell composed of eight dorsal plates. The chiton’s body itself, however, is unsegmented. A chiton can also use its foot to creep slowly over the rock surface. Chitons use their radula to scrape algae off the rock surface.

Question 44

Gastropoda

Answer 44

snails and slugs, Gastropods move literally at a snail’s pace by a rippling motion of their foot or by means of cilia—a slow process that can leave them vulnerable to attack. Most gastropods have a single, spiraled shell into which the animal can retreat when threatened. The shell, which is secreted by glands at the edge of the mantle, has several functions, including protecting the animal’s soft body from injury and dehydration. One of its most important roles is as a defense against predators

Question 45

Bivalvia

Answer 45

clams, oysters, and other bivalves. Bivalvia are all aquatic and include many species of clams, oysters, mussels, and scallops. Bivalves have a shell divided into two halves. The halves are hinged, and powerful adductor muscles draw them tightly together to protect the animal’s soft body. Bivalves have no distinct head, and the radula has been lost. Some bivalves have eyes and sensory tentacles along the outer edge of their mantle

Question 46

Cephalopoda

Answer 46

squids, octopuses, cuttlefishes, and chambered nautiluses. Cephalopods are active marine predators. They use their tentacles to grasp prey, which they then bite with beak-like jaws and immobilize with a poison present in their saliva. The foot of a cephalopod has become modified into a muscular excurrent siphon and part of the tentacles

Question 47

a closed circulatory system

Answer 47

in which the blood remains separate from fluid in the body cavity

Question 48

ammonites

Answer 48

Shelled cephalopods called, some of them as large as truck tires, were the dominant invertebrate predators of the seas for hundreds of millions of years until their disappearance during the mass extinction at the end of the Cretaceous period, 66 million years ago

Question 49

Threats to molluscs are especially severe in two groups:

Answer 49

freshwater bivalves and terrestrial gastropods

Question 50

Annelids

Answer 50

segmented worms that live in the sea, in most freshwater habitats, and in damp soil. Annelids, which have a coelom (and no hemocoel), range in length from less than 1 mm to more than 3 m

Question 51

Polychaeta

Answer 51

the polychaetes, a paraphyletic group

Question 52

Oligochaeta

Answer 52

the oligochaetes, a subgroup of the polychaetes

Question 53

Hirudinea

Answer 53

the leeches, a subgroup of the oligochaetes

Question 54

errantians

Answer 54

many errantians are mobile; some swim among the plankton (small, drifting organisms), while many others crawl on or burrow in the seafloor. Many are predators, while others are grazers that feed on large, multicellular algae. The group also includes some relatively immobile species

Question 55

Sedentaria

Answer 55

Sedentaria, tend to be less mobile than those in Errantia. Some species burrow slowly through marine sediments or soil, while others live within tubes that protect and support their soft bodies. Tube-dwelling sedentarians often have elaborate gills or tentacles used for filter feeding

Question 56

a cuticle

Answer 56

a tough external coat

Question 57

molting

Answer 57

aka ecdysis, or when a cuticle is shed

Question 58

nematodes

Answer 58

nematodes , or roundworms, are found in most aquatic habitats, in the soil, in the moist tissues of plants, and in the body fluids and tissues of animals. The cylindrical bodies of nematodes range from less than 1 mm to more than 1 m long, often tapering to a fine tip at the posterior end and to a blunter tip at the anterior end. A nematode’s body is covered by a tough cuticle (a type of exoskeleton); as the worm grows, it periodically sheds its old cuticle and secretes a new, larger one. Nematodes have an alimentary canal, though they lack a circulatory system. Nutrients are transported throughout the body via fluid in the hemocoel. The body wall muscles are all longitudinal, and their contraction produces a thrashing motion.

Question 59

arthropods

Answer 59

with segmented body, hard exoskeleton, and jointed appendages

Question 60

an open circulatory system

Answer 60

in which fluid called hemolymph is propelled by a heart through short arteries and then into the hemocoel—the body cavity surrounding the tissues and organs

Question 61

Chelicerates

Answer 61

(clade Chelicerata) are named for clawlike feeding appendages called chelicerae, which serve as pincers or fangs. Chelicerates lack antennae, and most have simple eyes (eyes with a single lens).

Question 62

book lungs

Answer 62

gas exchange is carried out by book lungs, stacked platelike structures contained in an internal chamber (Figure 33.33). The extensive surface area of these respiratory organs enhances the exchange of and between the hemolymph and air

Question 63

complete metamorphosis

Answer 63

Insects with have larval stages specialized for eating and growing that are known by such names as caterpillar, maggot, or grub. The larval stage looks entirely different from the adult stage, which is specialized for dispersal and reproduction.

Question 64

echinoderms

Answer 64

slow-moving or sessile marine animals. Echinoderms have a coelom. A thin epidermis covers an endoskeleton of hard calcareous plates, and most species are prickly from skeletal bumps and spines

Question 65

water vascular system,

Answer 65

a network of hydraulic canals branching into extensions called tube feet that function in locomotion and feeding