Chapter 34: The Invertebrates (Part 2, Week 7)

Question 1

[Start 34.4 Lophotrochozoa: The Flatworms, Rotifers, Bryozoans, Brachiopods, Mollusks, and Annelids]

What are the three clades of bilateral animals?

Answer 1

Lophotrochozoa
Ecdysozoa

Collectively known as protostomes

Deuterostomia

Question 2

How many phylums does Lophotrochozoa contain?

Answer 2

6!

Question 3

What is the phylum called, within lophotrochozoa, that are flatworms that lack a specialized respiratory or circulatory system and must respire by diffusion?

Answer 3

Platyhelminthes (from the Greek platy, meaning flat, and helminth, meaning worm)

Question 4

Why is the flat shape within flatworms so important?

Answer 4

Because they must respire through diffusion and they do not have a respiratory system, no cell can be too far from the surface, making a flattened shape necessary.

Question 5

What were the first animals to develop an active predatory lifestyle?

Answer 5

Flatworms

However, most species are internal or external parasites.

Question 6

Since flatworms are hypothesized to be the first bilaterian animals, what did they evolve? Think layers.

Answer 6

Evolve three distinctive embryonic germ layers—ectoderm, endoderm, and mesoderm.

The mesoderm replaced the simplier gelatinous mesoglea of cnidarians.

For this reason, they are said to be triploblastic.

Question 7

What are the muscles within flatworms derived from within their three layers that are very well developed?

Answer 7

The mesoderm.

Question 8

What was a critical innovation in animals, that led to the development of more sophisticated organs?

Answer 8

The evolution of mesoderm!

Question 9

What do flatworms lack, which is a fluid-filled body cavity in which the gut is suspended, and therefore they are classified as acoelomates?

Since flatworms lack this, the medoderm fills the body spaces around the gastrovascular cavity.

Answer 9

A coelem.

The coelomic fluid serves several functions: it acts as a hydroskeleton; it allows free movement and growth of internal organs; it serves for transport of gases, nutrients and waste products around the body; it allows storage of sperm and eggs during maturation; and it acts as a reservoir for waste.

Question 10

What do cnidarians and flatworms have in common which pertains to a part of their incomplete digestive system?

Answer 10

They only have one opening that serves as the mouth and anus.

Question 11

In most flatworms, they posses a muscular WHAT that may be extended through the mouth and opens to a gastrovascular cavity where food can be digested?

In large flatworms, the gastrovascular cavity is highly branched to distribute nutrients to all parts of the body.

Answer 11

A muscular pharynx.

Question 12

How do flatworms breathe?

Answer 12

Having no specialized respiratory or circulatory system, flatworms obtain oxygen by diffusion. A flattened shape ensures that no cells are too far from the body surface.

Question 13

What simple excretory organs found in flatworms that are used to filter out wastes and excess water?

Answer 13

Protonephridia

Question 14

What is a cell that exists primarily to maintain osmotic balance between an organism’s body and surrounding fluids in a flatworm they are located at the branched caps of lateral canals in the protonephridia?

Answer 14

Flame cells.

Protonephridia are dead-end tubules lacking internal openings. The flame cells, which are ciliated and waft water through the lateral canals to the outside primarily function in maintaining osmotic balance between the flatworm’s body and the surrounding fluids.

Question 15

What was the development of the protonephridia system key to permitting?

Answer 15

The movement of animals into freshwater habitats and even moist terrestrial areas.

Question 16

T/F Platyhelminthes are bilaterally symmetrical.

Answer 16

True.

Question 17

What is the localization of sensory structures at the anterior end of an animal’s body?

Answer 17

Cephalization

Flatworms have head bearing sensory appendages.

Question 18

What is at the anterior end of some free-living flatworms which are light-sensitive eyespots?

Answer 18

Ocelli (same as the jellyfish!)

Question 19

What are the chemoreceptive and sensory cells that are concentrated in organs near the ocelli?

Answer 19

Auricles (they help find food rather than light, which is accomplished by ocelli.)

Question 20

What is a paried structure in the head of invertebrates that recieves input from senory cells (i.e., ocelli and auricles) and controls motor output?

Answer 20

Cerebral ganglia

Question 21

What travels from the ganglia (sensory input collector) in a pair and runs the length of the body from the anterior to the posterior?

Also, transverse nerves form a nerve net on the ventral surface, similar to that of cnidarians.

Answer 21

Lateral nerve cords

Thus, flatworms show the beginnings of the more centralized type of nervous system seen throughout much of the rest of the animal kingdom.

Question 22

What are the four classes of flatworms or platyhelminthes? Answer by way of species count.

Answer 22

Trematoda (Flukes) 11,000 species
- Internal parasites of vertebrates; complex life cycle with several intermediate hosts.

Cestoda (tapeworms) 5,000 species
- Internal parasites of vertebrates; complex life cycle, usually with one intermediate host; no digestive system; nutrients absorbed across epidermis

Tuberllaria (planarians) 3,000 species
- Mostly marine; only free-living class of flatworms; predatory or scavengers

Monogenea (fish flukes) 1,000 species
- Marine and freshwater; usually only external parasites of fish; simple life cycle (no intermediate host)

Question 23

What 2 classes of flatworms or platyhelminthes are internally parasitic in humans and other animals and therefore are of great medical and veterinary importance?

Answer 23

Cestodes and trematodes

They possess a variety of organs of attachment, such as hooks and suckers, that enable them to remain embedded within their hosts. For example, cestodes attach to their host by means of anorgan at the head end called a scolex.

They have no mouth or gastrovascular cavity and absorb nutrients across the body surface.

About 1% of U.S. cattle are infected by beef tapeworms. Consuming beef that is not sufficiently well cooked can lead to infection by these parasites. At least 1,000 hospitalizations a year in the U.S. are due to tapeworm infection, most as a result of eating uncooked pork.

Question 24

Reproduction Facts about Flatworms

• Reproduction is either sexual or asexual.
• Most species are hermaphroditic but do not fertilize their own eggs.
• Flatworms can also reproduce asexually by splitting into two parts, with each half regenerating the missing fragment.

Answer 24

N/A

Question 25

What requires two different vertebrae host species, such as pigs or cattle, to begin their life cycle and another host, such as humans to complete their development?

Answer 25

Cestodes

Behind the scolex in cestodes is a long ribbon of identical segments called proglottids, which are segments of sex organs that produce thousands of eggs.

The proglottids are continually shed in the host’s feces. Human feces passed out onto the ground are eaten with grass by pigs and cattle. Many tapeworms are ingested by humans who consume undercooked, infected meat—hence it is important to cook meat thoroughly.

Question 26

What class of platyhelminthes has life cycle more complex than that of cestodes which involves multiple hosts where the intermediate host is a mollusk and the final host, or definitive host, is a vertebrate?

Answer 26

Trematodes

Often a second or even a third intermediate host is involved.

In the case of the Chinese liver fluke, the adult parasite lives and reproduces in the definitive host, a human.

Structures, which are sometimes called eggs, contain encapsulated miracidia; these pass from the host via the feces, and then an intermediate host, such as a snail, eats the miracidia, which transform into sporocysts.

The sporocysts asexually produce more sporocysts called rediae, which develop into a free-swimming life stage called cercariae.

In the last stages of the life cycle, cercariae bore their way out of the snail and infect their second intermediate host, fishes, by entering via the gills. Here, the cercariae develop into juvenile flukes and lodge in fish muscle, which the definitive host will eat.

From the smalli ntestine of the definitive host, the juvenile flukes travel to the liver and grow into adult flukes, and the life cycle begins anew. The probability of each trematode stage reaching a suitable host is low, so trematodes produce large numbers of off spring to ensure that some survive.

Question 27

How can infection by the blood fluke, which is a common parasitic trematode, that causes shistosomiasis in 200 million people worldwide?

Answer 27

Sewage treatment and access to clean water greatly reduce infection rates.

Inch long adult flukes can live in humans for years (gross)

Question 28

What phylum within lophotrochazoa get their name from their cilated crown, or corona, which, when beating, looks similar to a rotating wheel?

Answer 28

Rotifera (from the Latin rota, meaning wheel, and fera, meaning to bear)

Question 29

Facts about Rotifers

• Most rotifers are microscopic animals, usually less than 1 mm long, and some have beautiful colors.
• They typically inhabit fresh water, with a few marine and terrestrial species.
• Most often they are bottom-dwelling organisms, living on a pond floor or along lakeside vegetation.
• The body of the rotifer bears a jointed foot with one to four toes. Pedal glands
  in the foot secrete a sticky substance that aids in attachment to a substrate.
• They also have a pair of protonephridia with flame bulbs that collect excretory and digestive waste and drain into a bladder, which passes waste to the anus.
• The nervous system consists of nerves that extend from the sensory organs, especially the eyespots and some bristles on the corona, to the brain.

Answer 29

N/A

Question 30

What do the internal organs of rotifers lie within that is a fluid-filled body cavity that IS NOT completely lined with mesoderm and serves as a hydrostatic skeleton and as a medium for the internal transport of nutrients and wastes?

Answer 30

A pseudocoelom (hence the pseudo)

Question 31

What is different about rotifers than its other lophotrochazoa ancestors that pertains to eating and eliminating waste?

Answer 31

It has an alimentary canal, a digestive tract with a separate mouth and anus.

They feed much more frequently than simpler animals such as cnidarians.

Question 32

What creates water currents that propel the animal through the water and waft small planktonic organisms or decomposing organic material toward the mouth?

Answer 32

The corona.

Question 33

What is the circular muscular pharynx in the mouth of rotifers, which as jaws for grasping and chewing?

Answer 33

Mastax.

The mastax, which in some species can protrude through the mouth to seize small prey, is a structure unique to rotifers.

Question 34

Reproduction facts of Rotifers

Reproduction in rotifers is unique.

• In some species, unfertilized diploid eggs that have not undergone meiotic division develop into females through a process known as parthenogenesis
• In other species, some unfertilized eggs develop into females, whereas others develop into males that live only long enough to produce and release sperm that fertilize the eggs.
• The resultant fertilized eggs form zygotes, which have a thick shell and can survive for long periods of harsh conditions, for example, if a water supply dries up, before developing into new females.
• Because the tiny zygotes are easily transported, rotifers show up in the smallest of aquatic environments, such as bird baths or roof gutters.

Answer 34

N/A

Question 35

Facts about Bryozoa and Brachiopodia!

• Both possess a lophorphore, a cillary feeding device. The lophophore is a circular fold of the body wall bearing tentacles that draw water toward the mouth.
• The first true coelom!!! A body cavity, located between the intestinal canal and the body wall.
• A thin extension of the coelom penetrates each tentacle, the tentacles also serve as a respiratory organ. Gases diffuse across the tentacles and into or out of the coelomic fluid and are carried throughout the body.
• Both phyla have a U-shaped alimentary canal, with the anus located near the mouth but outside of the lophophore.

Answer 35

N/A

Question 36

Their name meaning moss and zoon, are small colonial animals, most of which are less than 0.5 mm long, that can be found on rocks in shallow aquatic environments. They look very much like plants. Within a colony, each animal secretes and lives inside a nonliving exoskeleton called a zoecium that is composed of chitin or calcium carbonate.

What is it?

Answer 36

Bryozoans of the phylum Bryozoa

Forthis reason, bryozoans have been important reef-builders. Also, many of them encrust boat hulls and have to be scraped off periodically. About 4,500 species of bryozoans currently exist. They date back to the Paleozoic era, and thousands of fossil forms have been discovered and identified.

Question 37

What are the two main functions of the lophophore?

Answer 37

The lophophore functions as (1) a ciliary feeding device and (2) a respiratory organ.

Question 38

What phylum are marine organisms with two shell halves, like clams, and have a dorsal and ventral shell, with the plane of symmetry perpendicular to the site at which the shells join?

Answer 38

Bachiopodia

Clams, however, have their plane of symmetry parallel to the site where the two shells join.

Question 39

Facts about Brachipodia

• Brachiopods are bottom-dwellingspecies that attach to the substrate via a muscular pedicle (like plants!)
• Some of these fossil forms represent organisms that reached 30 cm in length, although their modern relatives are only 0.5–8.0 cm long.

Answer 39

N/A

Question 40

T/F Mullusks are marine animals.

Answer 40

False, some have colonized fresh water habitats.

Question 41

Even though many snails and slugs have moved onto land, why can they only survive?

Answer 41

Humid areas and where the calcium necessary for shell formation is abundant in the soil.

Question 42

What led to the ability of diversification of mollusk body plans?

Answer 42

The ability to colonize freshwater and terrestrial habitats.

Question 43

Even though great variation in morphology occurs between classes of mollusks, what are the three basic body parts in the body plan?

Answer 43

• A muscular foot is usually used for movement, and a visceral mass
  containing the internal organs rests atop the foot.
• The mantle, a fold of skin draped over the visceral mass, secretes a shell in those species that form shells.
• The mantle cavity houses delicate
  gills, filamentous organs that are specialized for gas exchange.

A continuous current of water, often induced by cilia present on the gills or by muscular pumping, flushes out the wastes from the mantle cavity and brings in new oxygen-richwater.

Question 44

Review: the common body plan of mollusks

1. What is a muscular structure used for movement?
2. What is a structure that rests atop the foot and contains the internal organs?
3. What is a fold of skin drapped over the visveral mass that secretes a shell in those species that form shells?
4. What is the chamber in a mollusk mantle that houses delicate gills?
5. What are specialized filamentous organs in aquatic animals that are used to obtain oxygen and eliminate wastes?

Answer 44

1. The foot
2. Visceral mass
3. Mantle
4. Mantle cavity
5. Gills

Question 45

Do molluscan hearts pump blood?

Answer 45

Technically, the hearts of most mollusks pump hemolymph into vessels and then into tissues.

The hemolymph collects in open, fluid-filled cavities called sinuses, which flow into the gills and then back to the heart.

This is known as an open circulatory system. Only closed circulatory systems pump blood, as occurs in the cephalopods.

Question 46

Even though mollusks are coelomate organisms, what is the coeclom confined to?

Answer 46

A small area around the heart.

Question 47

What are the open, fluid-filled cavaties between internal organs within mollusks that are continually bathed in hemolymph which is the bodily fluid pumped in from the heart?

Known as an open circulatory system.

In animals, a circulatory system in which hemolymph, which does not differ from the interstitial fluid, flows throughout the body and is not confined to special vessels.

Answer 47

Sinuses.

The sinuses coalesce to form an open cavity known as the hemocoel (blood cavity). From these sinuses, the hemolymph drains into vessels that take it to the gills and then back tothe heart.

Question 48

What are excretory filtration organs found in a variety of invertebrates, including annelids?

They also have have ciliated funnel-like openings inside the coelom that are connected to ducts that lead to the exterior mantle cavity.

Answer 48

Metanephridia

The pores from the metanephridia discharge wastes into this cavity.

The anus also opens into the mantle cavity. The metanephridial ducts may also serve to discharge sperm or eggs from the gonads.

Question 49

How does the nervous system vary in mollusks?

Answer 49

The nervous system varies from simple ganglia and nerve chords in most species to much larger brains and sophisticated organs of touch, smell, taste, and vision in octopuses.

Question 50

What is a unique, protrusible, tonguelike organ in a mollusk that has many teeth and is used to eat plants, scrape food particles off rocks, or bore into shells of other species?

Answer 50

Radula

In the cone shells, the radula is reduced to a few poison-injecting teeth on the end of a long proboscis that is cast about in search of prey, such as a worm or even a fish.

Some cone shell species produce a neuromuscular toxin that can kill humans. Other mollusks, particularly bivalves, have lost their radula and are filter feeders that strain water brought in by ciliary currents.

Question 51

What are complex three-layered structures that are secreted by the mantle and continue to grow as the mollusk grows?

Answer 51

Mollusk shells!

Shell growth is often seasonal, resulting in distinct growth lines on the shell, much like tree rings.

Using shell growth patterns, biologists have discovered some bivalves that are over 100 years old.

The innermost layer of the shells of oysters, mussels, abalone, and other mollusks is a smooth, iridescent lining called nacre, which is commonly known as mother-of-pearl and is often collected from abalone shells for jewelry.

Actual pearl production in mollusks, primarily oysters, occurs when a foreign object, such as a grain of sand, becomes lodged between the shell and the mantle, and layers of nacre are laid down around it to reduce the irritation.

Question 52

What is interesting about reproduction in mollusks that was not previously observed in platyhelminthes, rotifera, bryozoa, or brachiopoda?

Answer 52

While some do exist as hermaphrodites, most species have separate sexes.

Gametes are usually released into the water, where they mix and fertilization occurs. In some snails, however, fertilization is internal, with the male inserting sperm directly into the female.

Question 53

What was a critical innovation that enabled some snails to colonize land?

Answer 53

Internal fertilization where the male inserts sperm directly into the female.

Question 54

What, in mollusks, is a free-swimming larva that has a rudimentary foot, shell, and mantle?

Answer 54

A veliger

Question 55

Of the eight major molluscan classes, what are the four most common and what are some facts of each?

Order by number of species discovered so far!

Answer 55

Gastropoda (snails, slugs, nudibranchs) 75,000 species
- Marine, freshwater, or terrestrial; most with coiled shell, but shell abscent in slugs and nudibranches; radula present

Bivalvia (clams, mussels, oysters, scallops) 30,000 species
- Marine or freshwater; shell with two halves or valves; primarily filter feeders with siphons

Polyplacophora (chitons) 860 species
- Marine; eight-plated shell

Cephalopoda (octopuses, squids, nautiluses) 780 species
- Marine; predatory, with tentacles around mouth, often with suckers; shell often abscent or reduced; closed circulatory system; jet propulsion via siphon

Question 56

What are the most morphologically complex of the mollusks and indeed among the most complex of all invertebrates and are fast-swimming marine predators that rangefrom organisms just a few centimeters in size to the colossal squid, which is known to reach over 13 m in length and 495 kg (1,091 lb) in weight?

Answer 56

The cephalopoda (from the Greek kephalo, meaning head, and podos, meaning foot)

A cephalopod’s mouth issurrounded by many long arms commonly armed with suckers. All cephalopods have a beak-like jaw that allows them to bite their prey, and some, such as the blue-ringed octopus, delivera deadly poison through their saliva.

Question 57

What is a large phylum with about 1800 species of segmented worms and the members include free-ranging marine worms, tube worms, the familiar earthworms, and leeches and range in size from less than 1 mm to enormous Austrailian earthworms that can reach a length of 3 meters?

Answer 57

The Annelids!

Question 58

What is the phylum name Annelida derived from in Latin?

Answer 58

Annulus, meanin little ring.

Each ring is a distinct segment of the annelid’s body; adjacent segments are separated by septa.

Question 59

What three advantages does segmentation in annelids confer?

Answer 59

1. Many components of the body are repeated in each segment, including blood vessels, nerves, and excretory and reproductive organs. If the components in one segment fail, those of another segment will still function.
2. The fluid-filled coelom acts as a hydrostatic skeleton. In unsegmented coelomate animals, muscle contractions can distort the entire body during movement. However, such distortion is minimized in segmented animals, which allows for more effective locomotion over solid surfaces.
3. Segmentation permits specialization of some segments, especially at the annelid’s anterior end. Animals with more complex body plans tend to produce a greater variety of specialized segments.

Question 60

What do all annelids have, except the leeches, ON each segment and it consists of chitinous bristles in the integument of many invertebrates?

Answer 60

Setae (See-ti)

Question 61

Where are setae sometimes situated on some annelids that are pushed into the substrate to provide traction during movement?

Hint: (from the Greek, meaning almost feet)

Answer 61

on fleshy, footlike Parapodia.

Question 62

T/F Some annelids can extract nutrients from soil, dead or living vegetation, or be predatory or parastic?

Answer 62

True

Question 63

Where does the pair of cerebral ganglia on a annelid’s nervous system connect to?

And from there, what is it connected to?

Answer 63

Subpharyngeal ganglion

Ventral nerve cord

Question 64

What does the ventral nerve cord contain that consists of few very large nerve cells that facilitate high-speed neuronal conduction and rapid responses to stimuli?

Answer 64

Giant Axons

A very large axon in certain species such as squids that facilitates high-speed neuronal conduction and rapid responses to stimuli.

Question 65

Within annelids, what carries nutrients, wastes, and respiratory gases? (2)

Answer 65

The circulatory system AND the coelomic fluid.

The circulatory system is closed, with dorsal and ventral vessels connected by pairs of pulsating vessels.

The blood of most annelid species contains the respiratory pigment hemoglobin.

Respiration occurs directly through the permeable skin surface, which restricts annelids to moist environments.

The digestive system is complete and unsegmented, with many specialized regions: mouth, pharynx, esophagus, crop, gizzard, intestine, and anus.

Question 66

How does reproduction happen in Annelids? (3)

Answer 66

Sexual reproduction involves two individuals, often of separate sexes.

Hermaphroditic exchange sperm via internal fertilization.

In some species, asexual reproduction by fission occurs in which the posterior part of the body breaks off and forms a new individual.

Question 67

What are the two major groups within the phylum Annelida?

Answer 67

Errantia and Sedentaria.

Question 68

How do the member of Errantia and Sedentaria differ?

Answer 68

Members of the Errantia havemany long setae bristling out of their body and are supported on footlike parapodia.

Most Errantia are free-ranging predators with well-developed eyes and powerful jaws. Many are brightly colored. In turn, most species are important prey for fi shes and crustaceans.

In the Sedentaria, setae are in close proximity to the body wall, which facilitates anchorage in tubes and burrows. The more sedentary lifestyle of the Sedentaria is associated with reductions in head appendages. Within this group, three types of lifestyles are apparent: those of tubeworms, earthworms, and leeches.

Question 69

What are tube worms within the group of Sedentaria of the phylym, Annelids?

Answer 69

Tube worms are marine sedentarians that exhibit beautiful tentacle crowns for filtering food items, such as plankton, from the water. The bulk of the worm remains hidden in a tube deep in the mud or sand.

Question 70

Fun Facts of Earthworms!

• Unique and beneficial role in conditioning the soil, primarily due to their burrows and excretion.
• They ingest soil and leaf tissue to extract nutrients and in the process create burrows in the earth.
• As plant material and soil pass through the earthworm’s digestive system, it is finely ground in the gizzard intosmaller fragments. Once excreted, this material—called castings—enriches the soil.
• Because a worm can eat its own weight in soil every day, worm castings on the soil surface can be extensive.
• The biologist Charles Darwin was interested in earthworm activity, and his last work, The Formation of Vegetable Mould, through the Actions of Worms, with Observations on Their Habits, was the first detailed study of earthworm ecology. In it, he wrote, “All the fertile areas of this planet have at least once passed through the bodies of earthworms.”

Answer 70

N/A

Question 71

What typically has a fixed number of segments, usually 34, though in many species septa are not present and are typically blood-sucking parasites of vertebrates?

Answer 71

Leeches.

Unlike cestode and trematode flatworms, which are internally parasitic and host-specific, leeches are generally external parasites that feed on a broad range of hosts, including fishes, amphibians, and mammals.

Leeches have powerful suckers at both ends of the body, and the anterior sucker is equipped with razor-sharp jaws that can bore or slice into the host’s tissues.

Question 72

What within leeches salivary secreation acts as as an anticoagulant to stop the prey’s blood from clotting and an anesthetic to numb the pain?

Answer 72

Hirudin

They were once used in the medical field in the practice of bloodletting, the withdrawal of often considerable quantities of blood from a patient in the erroneous belief that this would prevent or cure illness and disease.

Question 73

Why would leeches be used today after surgeries?

Answer 73

If the blood vessels are not fully reconnected and excess blood accumulates, a swelling called a hematoma may form.

The accumulated blood blocks the delivery of new blood and stops the formation of new vessels. The leeches remove the accumulated blood, and new capillaries are more likely to form.