Bio 2 Chapter 33

Bdelloids

Rotifer that reproduces by parthenogenesis. There are no males. can tolerate very high levels of desiccation. When conditions improve and their cells rehydrate, DNA from other species enters their cells through cracks in the plasma membrane. Recent evidence suggests that this foreign DNA can be incorporated into the bdelloids' genome, thereby leading to increased genetic diversity.

What two are pseudocoelomates

Rotifers and Nemotodes

parthenogenisis

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

Cnidocytes

Special stinging structures on cnidarians tentacles that look like small harpoons.

How doe asteroidia eat

They turn there stomach inside out secreting juices begin digesting the mollusc within its own shell. The sea star then brings its stomach back inside its body, where digestion of the mollusc's (now liquefied) body is completed

in crustaceans, walking legs are present on the _________________, and, unlike their terrestrial relatives, the insects, crustaceans also have appendages on their post-genital region, or "tail."

Thorax

in crustaceans how many appendages are modified as mouthparts, including the hard mandibles

Three or more pairs

Holothuroidea (sea cucumbers)

Sea cucumbers lack spines, have a very reduced endoskeleton, and do not look much like other echinoderms Sea cucumbers have five rows of tube feet; some of these are developed as feeding tentacles

Choanocytes (collar cells)

a flagellated cell with a collar of protoplasm at the base of the flagellum, numbers of which line the internal chambers of sponges.

mesohyl

a gelatinous region between the two layers of cells of a sponge

A land snail, a clam, and an octopus all share distinct cephalization. a mantle. embryonic torsion .a radula .gills.

a mantle

Molluscs are coelomates, and their bodies have three main parts:

a muscular foot, usually used for movement; a visceral mass containing most of the internal organs; and a mantle, a fold of tissue that drapes over the visceral mass and secretes a shell (if one is present).

Chelicerata

a sub phylum of arthropods; includes Horseshoe crabs, spiders, scorpions, mites etc.

Myriapods

centipedes and millipedes

Which mollusk has a closed circulatory system

cephalopods

Chelicerates (clade Chelicerata) are named for clawlike feeding appendages called

chelicerae, which serve as pincers or fangs.

arthropods consist of three major lineages that diverged early in the phylum's evolution:

chelicerates (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders) myriapods (centipedes and millipedes) pancrustaceans (a recently defined, diverse group that includes insects as well as lobsters, shrimp, barnacles, and other crustaceans).

The phylum Arthropoda includes four major lineages:

cheliceriforms (also called chelicerates); myriapods; insects and their relatives (together called hexapods); and crustaceans.

The similarity between ______________________ in sponges and the cells of choanoflagellates supports molecular evidence suggesting that animals evolved from a choanoflagellate-like ancestor

choanocytes

The lining the interior of the spongocoel are flagellated ________________________________. These cells engulf bacteria and other food particles by phagocytosis

choanocytes, or collar cells (named for the finger-like projections that form a "collar" around the flagellum)

The collar cells of sponges bear a striking resemblance to a

choanoflagellate cell.

molluscs of the clade Bivalvia are all aquatic and include many species of

clams, oysters, mussels, and scallops.

What is reduced in a mollusk

coelom

Cephalization

concentration of sense organs and nerve cells at the front of an animal's body

shrimplike krill

copepod, crustacean, pancrustean, arthropoda, ecdyzoa

planktonic crustaceans

copepods

The only arthropods with two pairs of antennae are ___.

crustaceans

Most __________________________ live in tropical oceans and are equipped with highly toxic cnidocytes

cubozoans

Polyps

cylindrical tubes with mouth and tentacles facing upward

One species of soil nematode, ____________________________________, however, is very well studied and has become a model research organism in biology

Caenorhabditis elegans

These are colonial animals that superficially resemble clumps of moss.

Ectoprocts (from the Greek ecto, outside, and procta, anus)

annelids can be divided into two major clades

Errantia and Sedentaria

To date, however, the oldest fossil that is widely accepted as a bilaterian is of __________________________(or close relative) that lived 560 million years ago

Kimberella, a mollusc

Some planarians can reproduce asexually through ___________________ The parent constricts roughly in the middle of its body, separating into a head end and a tail end; each end then regenerates the missing parts. Sexual reproduction also occurs. Planarians are ______________________________, and copulating mates typically cross-fertilize each other.

fission. hermaphrodites

4 ways to maximizing Surface Area

flattening, folding, branching and projections

Platyhelminthes

flatworms (tapeworms, planarians, flukes); bilateral symmetry; central nervous system

Diptera

flies and mosquitoes

flatworms include many parasitic species, such as

flukes and tapeworms

All molluscs have inherited a _____________from their common ancestor. However, in different groups of molluscs, the structure has been modified over time by natural selection. In gastropods, it is used as a ________________________________________. In cephalopods, its has been modified into part of the tentacles and into an ___________________________, through which water is propelled (resulting in movement in the opposite direction).

foot holdfast or to move slowly on the substrate excurrent siphon

Medusae include ________________________________. The tentacles of a jelly dangle from the oral surface, which points downward.

free-swimming jellies

man made Threats to molluscs are especially severe in two groups,

freshwater bivalves and terrestrial gastropods

About three-quarters of all living species of molluscs are

gastropods

The basic body plan of a cnidarian is a sac with a central digestive compartment, the ______________________________________ A single opening to this cavity functions as both mouth and anus.

gastrovascular cavity.

Small crustaceans exchange gases across thin areas of the cuticle; larger species have _________________. Nitrogenous wastes also diffuse through thin areas of the cuticle, but a pair of glands regulates the salt balance of the hemolymph.

gills

Do annelids have a digestive tract

have a complete, one-way digestive tract with a mouth and anus. The digestive tract is not segmented.

Hemolymph reenters the arthropod heart through pores that are usually equipped with valves. The hemolymph-filled body sinuses are collectively called the ______________________, which is not part of the coelom.

hemocoel

Most molluscs have separate sexes, and their gonads (ovaries or testes) are located in the visceral mass. Many snails, however, are .

hermaphrodites

A land snail, a clam, and an octopus all share A. a mantle. B. a radula. C gills. D. distinct cephalization.

mantle

In many molluscs, the mantle extends beyond the visceral mass, producing a water-filled chamber, ______________________________ which houses the gills, anus, and excretory pore

mantle cavity,

sea spiders (pycnogonids) and horseshoe crabs

marine chelicerates

Both the polyp and the medusa are composed of an outer epidermis and an inner gastrodermis separated by a gelatinous layer, the _____________

mesoglea

The body of a sponge consists of two layers of cells separated by a gelatinous region called the

mesohyl

Snails and slugs, oysters and clams, and octopuses and squids are all

molluscs (phylum Mollusca)

centipedes and millipedes

myriapods

Specialized cnidae called __________________________ contain a stinging thread that can penetrate the body wall of the cnidarian's prey.

nematocysts

Do flatworms have a digestive track

no

In the incomplete metamorphosis of grasshoppers and some other insect groups, the young called _______________ resemble adults but are smaller, have different body proportions, and lack wings

nymphs

Cepholapods

octupus, squid, nautilus, cuttlefish

Unlike millipedes, centipedes are carnivores. Each segment of a centipede's trunk region has

one pair of legs

Placazoa species

only 1 species ; Trichoplax Adhaeren

Like many molluscs, arthropods have an____________________________ , in which fluid called _____________________________is propelled by a heart through short arteries and then into spaces called sinuses surrounding the tissues and organs

open circulatory system hemolymph

insects as well as lobsters, shrimp, barnacles, and other crustaceans

pancrustaceans

the diverse group of organisms referred to as crustaceans are monophyletic, paraphyletic or polyphyletic

paraphyletic

In many errantians, each body segment has a pair of prominent paddle-like or ridge-like structures called ________________________ ("beside feet") that function in locomotion

parapodia

In Errantian, the gills

parapodia are richly supplied with blood vessels and also function as gills.

Trichinella spiralis

parasitic nematode occurring in the intestines of pigs and rats and human beings and producing larvae that form cysts in skeletal muscles. acquire this nematode by eating raw or undercooked pork or other meat (including wild game such as bear or walrus) that has juvenile worms encysted in the muscle tissue.

Trematodes

parasitic rhabditophoran, that usually requres intermediate host in which larvae develop before infecting the final host

Flatworms are in which phylum under what clade

phylum Platyhelminthes clade lophotrochozoan

oligochaetes are a subgroup of the

polychaetes

Terrestrial arthropods generally have internal surfaces specialized for gas exchange. For example, most insects have tracheal systems, branched air ducts leading into the interior of the body from

pores in the cuticle.

Posterior to the scolex is a long ribbon of units called ______________________ which are little more than sacs of sex organs.

proglottids,

clade Ecdysozoa includes animals that __________________________________________________as they grow; in fact, the group derives its name from this process, which is called ecdysis,

shed a tough external coat (cuticle)

Furthermore, the symmetry of adult echinoderms is not truly radial. For example, the opening (madreporite) of a sea star's water vascular system is not central but ______________________

shifted to one side.

Gastropods

snails and slugs

The silk by spiders is spun by organs called ______________________________ into fibers that then solidify.

spinnerets

Posterior to the mouth, rotifers have jaws called __________________that grind up food, mostly microorganisms suspended in the water

trophi

Hemiptera

true bugs, stink bugs

Millipedes have a large number of legs, though fewer than the thousand their name implies. Each trunk segment is formed from

two fused segments and bears two pairs of legs

__________________________________________known species are arthropods, and members of the phylum Arthropoda can be found in nearly all habitats of the biosphere

two out of every three

Unique to echinoderms is the __________________________ a network of hydraulic canals branching into extensions called tube feet that function in locomotion and feeding

water vascular system,

Acanthocephalans

"Thorny-headed" or "spiny-headed" worms group of highly modified "rotifers."

Catenulida

"chain worms," reproduce asexually by budding

Crinoidea (sea lilies and feather stars)

-Sea lilies live attached to the substrate by a stalk -Feather stars can crawl using long, flexible arms -Both are suspension feeders -Crinoidea have changed little over the course of evolution

Echinoidea (sea urchins and sand dollars)

-Sea urchins and sand dollars have no arms but have five rows of tube feet -Their spines are used for locomotion and protection -Sea urchins feed on seaweed using a jaw-like structure on their underside

Cnidarians (Hydra and Jellyfish)

-radial symmetry -polyp- body plan (vase shaped) which is mostly sessile -medusa- body plan (upside down bowl shaped) mostly motile -life cycle- free swimming larva to asexually producing (polyp) or sexual reproducing (medusa) -dipoblastic 2 cell layers only: ectoderm and endoderm connected by noncellular mesoglea -gastrovascular cavity where extracellular digestion occurs with one opening -all have stinging cells- cnidocytes- containing stingers, which are nematocysts

echinoderms reproduction

-sexual: mostly dioecious, external fertilization -asexual: by regeneration of body parts

What genetic changes led to the increasing complexity of the arthropod body plan? Arthropods today have _____ unusual Hox genes, both of which influence segmentation. But it is not because of this it is because of what?

2 driven by changes in the sequence or regulation of existing Hox genes

humans are hosts to at least _____ nematode species, including various pinworms and hookworms

50

Ecdysozoa includes about ________________animal phyla

8

Chitons have an oval-shaped body and a shell composed of ___________dorsal plates (Figure 33.17). The chiton's body itself, however, is _____________________________

8 unsegmented

Invertebrates account for over --- of known animal species.

95%

What (if anything) can be inferred about whether the common ancestor of each of the three major bilaterian clades had a true coelom? A The common ancestor of the Deuterostomia had a true coelom, but we cannot infer anything about the ancestor of the Lophotrochozoa or the Ecdysozoa. B The common ancestor of each of the three clades -- Lophotrochozoa, Deuterostomia, and Ecdysozoa -- had a true coelom. C We cannot infer anything about the status of the ancestor of the Lophotrochozoa, Ecdysozoa, or Deuterostomia. D The common ancestor of the Lophotrochozoa and the Deuterostomia had a true coelom, but we cannot infer anything about the ancestor of the Ecdysozoa.

A The common ancestor of the Deuterostomia had a true coelom, but we cannot infer anything about the ancestor of the Lophotrochozoa or the Ecdysozoa.

To what extent has the presence of a true coelom in animals changed over the course of evolution? A The presence or absence of a true coelom appears to have changed multiple times during the course of evolution. B The presence or absence of a true coelom appears to have changed exactly once during the course of evolution. C. It is impossible to tell whether the presence or absence of a true coelom has changed during the course of evolution. D. The presence or absence of a true coelom appears not to have changed during the course of evolution.

A The presence or absence of a true coelom appears to have changed multiple times during the course of evolution.

Planarians

A free-living flatworm found in unpolluted ponds and streams.

Medusa

A free-swimming cnidarian with a bell-shaped body and tentacles

Flatworms

A group of often parasitical worms that have bilateral symmetry, lack cardiovascular system, a one opening digestive system, and the beginnings of a brain; phylum platyhelminthes

osculum

A large opening on a sponge through which filtered water is expelled

echinoderms

A member of a group of slow moving or sessile marine animals characterized by a rough or spiny skin, a water vascular system, an endoskeleton, and a radial symmetry in adults, with examples such as sea stars, sea urchins and sand dollars

Isopods

A member of one of the largest groups of crustaceans, which includes terrestrial, freshwater, and marine species. Among the terrestrial isopods are the pill bugs, or wood lice.

incomplete metamorphosis

A type of metamorphosis with three stages: egg, nymph, and adult.

They are commonly called spiny-headed worms because of the curved hooks on the proboscis at the anterior end of their body

Acanthocephalans

Sea anemones and corals belong to the clade _______________ . These cnidarians occur only as ______________

Anthozoa polyps

Dueterostomes

Anus develops near blastopore Radial cleavage Daughter cells sit on top of previous cells. Mouth develops last. Echinodermata, Chordata,

Living echinoderms are divided into five clades

Asteroidea (sea stars and sea daisies) Ophiuroidea (brittle stars) Echinoidea (sea urchins and sand dollars) Crinoidea (sea lilies and feather stars) Holothuroidea (sea cucumbers)

The water vascular system of echinoderms A.. functions as a circulatory system that distributes nutrients to body cells. B. functions in locomotion and feeding. C. is bilateral in organization, even though the adult animal is not bilaterally symmetrical. D. moves water through the animal's body during filter feeding.

B

The vast majority of animal species belong to the clade _______________, whose members exhibit bilateral symmetry and triploblastic development

Bilateria

, or lamp shells, 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

Brachiopods

How does a blood fluke evade the immune systems of both snails and humans

By mimicking the surface proteins of its hosts, the blood fluke creates a partial immunological camouflage for itself. It also releases molecules that manipulate the hosts' immune systems into tolerating the parasite's existence.

which two main clades branch from the most recent common ancestor of the eumetazoans? a. Porifera and Cnidaria B. Lophotrochozoa and Ecdysozoa C. Cnidaria and Bilateria D. Deuterostomia and Bilateria

C

Trichoptera

Caddisflies

an explosion in insect diversity took place when insect flight evolved during the

Carboniferous and Permian periods (359-252 million years ago

flatworms separated into two lineages

Catenulida and Rhabditophora.

Amoebocytes (sponges)

Cells that are mobile using pseudopods and perform numerous functions, including reproduction, transport of food particles to nonfeeding cells, and manufacture tough skeletal fibers such as spicules within the mesohyl and flexible fibers such as spongin. most important they are totipotent (capable of becoming other types of sponge cells)

Ophiuroidea (brittle stars)

Characteristics of this class of echinoderm include: Arms that are distinct from central disk. Uses arms for locomotion and not tube feet. Unique photo-receptive organs. Some suspension eaters, some predators or scavengers.

sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders

Chelicerates

What kind of antennas do chelicerates have and what about their eyes?

Chelicerates lack antennae, and most have simple eyes (eyes with a single lens).

Which of the following combinations of phylum and description is incorrect? A. Echinodermata—bilateral symmetry as a larva, coelomate B. Nematoda—roundworms, pseudocoelomate C. Platyhelminthes—flatworms, gastrovascular cavity, acoelomate D. Porifera—gastrovascular cavity, coelomate

D

The best-known members of this group are freshwater species in the genus _______________________, commonly called planarians

Dugesia

complete metamorphosis

Insect development consisting of four stages: egg, larva, pupa, and adult. The transformation of a larva into an adult that looks very different, and often functions very differently in its environment, than the larva

the flatworms, rotifers and acanthocephalans, ectoprocts, brachiopods, molluscs, and annelids.

Lophotrochozoa; 6 listed of the 18 phyla

the phylum Cnidaria diverged into two major clades,

Medusozoa and Anthozoa

Millipedes and centipedes belong to the clade

Myriapoda

Do flatworms have a body cavity?

No, they are acoelomates

sea daisies

Only three species of sea daisies are known, all of which live on submerged wood. Disc shape no arms but small spines. daisies absorb nutrients through a membrane that surrounds their body.clade Asteroidea

sea stars (starfish)

Phylum Echinodermata have arms radiating from a central disk; the undersurfaces of the arms bear tube feet

Tapeworms

Phylum Platyhelminthes, subgroup rhabditophorans / parasitic. In many tapeworms, the anterior end, or scolex, is armed with suckers and often hooks that the worm uses to attach itself to the intestinal lining of its host. Tapeworms lack a mouth and gastrovascular cavity; they simply absorb nutrients released by digestion in the host's intestine. Absorption occurs across the tapeworm's body surface.

molluscs has evolved in various ways in the phylum's eight major clades. Name the 4 we discussed

Polyplacophora (chitons), Gastropoda (snails and slugs), Bivalvia (clams, oysters, and other bivalves), and Cephalopoda (squids, octopuses, cuttlefishes, and chambered nautiluses)

are 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

Polyps

Which of the following combinations of phylum and description is incorrect? Porifera-gastrovascular cavity, coelom present Nematoda-roundworms, pseudocoelomate Cnidaria-radial symmetry, polyp and medusa body forms Platyhelminthes-flatworms, gastrovascular cavity, acoelomate Echinodermata-bilateral symmetry as a larva, coelom present

Porifera-gastrovascular cavity, coelom present

Recent phylogenetic analyses have shown that two traditional animal phyla, the rotifers (former phylum Rotifera) and the acanthocephalans (former phylum Acanthocephala), should be combined into a single phylum, ________________________

Syndermata

Spongocoel

The central cavity of a sponge.

What (if anything) can be inferred about whether the common ancestor of each of the three major bilaterian clades had a true coelom? The common ancestor of the Deuterostomia had a true coelom, but we cannot infer anything about the ancestor of the Lophotrochozoa or the Ecdysozoa. The common ancestor of each of the three clades -- Lophotrochozoa, Deuterostomia, and Ecdysozoa -- had a true coelom. We cannot infer anything about the status of the ancestor of the Lophotrochozoa, Ecdysozoa, or Deuterostomia. The common ancestor of the Lophotrochozoa and the Deuterostomia had a true coelom, but we cannot infer anything about the ancestor of the Ecdysozoa.

The common ancestor of the Deuterostomia had a true coelom, but we cannot infer anything about the ancestor of the Lophotrochozoa or the Ecdysozoa.

Chordata

The phylum of the animal kingdom that includes vertebrates.

Catenulida and Rhabditophora

The two lineages of the phylum Platyhelminthes are the ________ and the ________.

Although the two medusae are genetically identical, a sperm produced by one will differ genetically from an egg produced by the other. In the figure, assume that the two medusae shown at step 4 were produced by one polyp colony. Select the answer that provides the correct reason. "Although the two medusae are genetically identical, a sperm produced by one will differ genetically from an egg produced by the other." True False (neither the medusae nor the gametes are genetically identical) False (both the medusae and the gametes are genetically identical) False (the medusae are not identical but the gametes are)

True

Although flatworms undergo triploblastic development, they are _________________________ (animals that lack a body cavity).

acoelomates

What are acoelomates? What is an example?

acoelomates are primitive animals no cavity Platy FLAT WORMS ARE ACOELOMATES

Corals live as solitary or colonial forms, often forming symbioses with

algae

In contrast to cnidarians and flatworms, which have a gastrovascular cavity, rotifers have an ______________________, a digestive tube with two openings, a mouth and an anus.

alimentary canal

Most bilaterians also have an ________________________________, which enables the stepwise digestion of a wide range of food particles.

alimentary canal

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, 65.5 million years ago.

ammonites

Starfish, Each tube foot consists of an _________________and a podium. When the __________________ squeezes, it forces water into the podium, which causes the podium to expand and contact the substrate. Adhesive chemicals are then secreted from the base of the podium, thereby attaching the podium to the substrate.

ampulla

Hymenoptera

ants, bees, wasps

The bulk of modern chelicerates are

arachnids, a group that includes scorpions, spiders, ticks, and mites

Rhabditophora

are more diverse than catenulida and include both free-living and parasitic species

Which phylum is characterized by animals that have a segmented body? Cnidaria Platyhelminthes Arthropoda Mollusca

arthropoda

Which invertebrate group has the most different kind of species

arthropoda over 1 million species

were among the first animals to colonize land, roughly 450 million years ago.

arthropods

Rotifers exhibit some unusual forms of reproduction

asexually by parthenogenesis sexually under certain conditions, such as high levels of crowding. The resulting embryos can remain dormant for years. Once they break dormancy, the embryos develop into another generation of females that reproduce asexually.

Caleoptera

beetles

echinoderm larvae have ____________________________ symmetry

bilateral

Biologists hypothesize that the diversity and success of arthropods are related to their

body plan—their segmented body, hard exoskeleton, and jointed appendages.

In most spiders, gas exchange is carried out by ________________________, stacked platelike structures contained in an internal chamber

book lungs

Lepidoptera

butterflies and moths

Cnidae

capsule-like organelles that are capable of exploding outward in cnidocytes

Centipedes: eating habits

carnivore

Lobsters, crayfishes, crabs, and shrimps are all relatively large crustaceans called

decapods

Millipedes eat ______________________________________________. They may have been among the earliest animals on land, living on mosses and early vascular plants.

decaying leaves and other plant matter

alimentary canal

digestive tube that extends from the mouth to the anus

some animal phyla with members that have deuterostome developmental features, including _________________________________, are not in the deuterostome clade.

ectoprocts and brachiopods

All animals except sponges and a few other groups are _____________________ ("true animals"), members of a clade of animals with tissues

eumetazoans

Cnidarians are an ancient phylum of

eumetazoans

The earliest chelicerates were ___________________, or water scorpions.

eurypterids

Examples of the polyp form include_____________ and ____________. Although they are primarily sedentary, many polyps can move slowly across their substrate using muscles at the aboral end of their body. When threatened by a predator, some sea anemones can detach from the substrate and "swim" by bending their body column back and forth, or thrashing their tentacles

hydras and sea anemones.

Cnidarians have diversified into a wide range of sessile and motile forms, including

hydras, corals, and jellies

Most ____________________ alternate between the polyp and medusa forms

hydrozoans

Almost all sponges exhibit sequential hermaphroditism: They function first as one sex and then as the other. Cross-fertilization can result when sperm released into the water current by an individual functioning as a male is drawn into a neighboring individual that is functioning as a female. The resulting zygotes develops to

into flagellated, swimming larvae that disperse from the parent sponge. After settling on a suitable substrate, a larva develops into a sessile adult.

As you might expect since all their cells are close to water, flatworms have no organs specialized for gas exchange, and their relatively simple excretory apparatus functions mainly to maintain osmotic balance with their surroundings. This apparatus consists of ______________________ networks of tubules with ciliated structures called _____________________ that pull fluid through branched ducts opening to the outside

protonephridia, flame bulbs

Internal organs lie within the ___________________, a body cavity that is not completely lined by mesoderm and serves as a cytoskeleton

pseudocoelom

Echinodermata

radially symmetrical marine invertebrates including e.g. starfish and sea urchins and sea cucumbers

Many molluscs feed by using a straplike organ called a _______________ to scrape up food.

radula

Syndermata

rotifers and acanthocephalans

Sponges are filter feeders: They filter out food particles suspended in the surrounding water as they draw it through their body, which in some species resembles a sac perforated with pores. Water is drawn through the pores into a central cavity, the ________________________, and then flows out of the sponge through a larger opening called the ________________________

spongocoel osculum

Arachnids have six pairs of appendages:

the chelicerae a pair of appendages called pedipalps that function in sensing, feeding, defense, or reproduction four pairs of walking legs.

Cnidarians have diversified into a wide range of sessile and motile There are two variations on this body plan:

the largely sessile polyp and the more motile medusa

All cnidarians that produce a medusa are members of clade Medusozoa, a group that includes

the scyphozoans (jellies) and cubozoans (box jellies), along with the hydrozoans

A nematode's body is covered by a

tough cuticle (a type of exoskeleton)

various flatworms that parasitize humans spend part of their lives in snail hosts. Around the world, about 200 million people are infected with _____________________________ called blood flukes (Schistosoma) and suffer from schistosomiasis, a disease whose symptoms include pain, anemia, and diarrhea.

trematodes

two ecologically and economically important subgroups of parasitic rhabditophorans, the

trematodes and the tapeworms.