Lab 2 (Flatworms, Nematodes, Molluscs)

Question 1

What is the basic knowledge from this lab of species?

Answer 1

• All have organ level organization
• Organ system (multiple organs work together to perform a particular function)
• Triploblastic (3 germ layers)
  1) Mesoderm (responsible for the development of many tissues, organs and systems)
• Most have a body cavity lined with mesodermal tissue called peritoneum (this cavity is called a coelom, and organisms that have one are called coelomates)
• Animals that lack a coelom are called acoelomates
• Bilateral symmetry (favours the development of bodies with distinct central nerve centres, and heads that possess sensory organs/structures)
• The possession of a head with sensory organs is called cephalisation

Question 2

What are the classes to the Phylum Platyhelminthes?

Answer 2

Class Turbellaria (planarians)
Class Cestoda (tapeworms)

Question 3

Explain the basics to the Phylum Platyhelminthes

Answer 3

• Flatworms
• Unusual critters
• Only triploblastic animals that do not have a proper coelom; they are acoelomates
• Instead of a coelom, the mesodermal space is filled with muscle and other fibres
• Have digestive and reproductive systems and a very simple nervous system
• No circulatory system (the flattened shape of their bodies permits oxygen to diffuse directly into their body cells from their environment)

Question 4

Explain the basics of the class turbellaria

Answer 4

• Planarians
• Little animals
• Live in freshwater and are free living
• Found on the underside of leaves, stones and other debris
• They glide on mucous, using cilia on their ventral surfaces ti power their movement
• They are not parasitic
• They are scavengers that feed on small animals and plants either living or dead
• Can regenerate lost body parts
• If cut in half, two new, complete animals will for from the two halves

Question 5

What is the nervous/sensory of planarians?

Answer 5

• Triangular head at the anterior end of the body that contains bundles of nerves called ganglia
• The bumps on either side are the auricles; these are sensory organs used for touch and olfaction, not hearing
• The head has two eyespots; these are light sensitive pigment cups
• The entire body is covered in chemoreceptive and tactile cells

Question 6

What is feeding/digestion of planarians?

Answer 6

• In the middle of the body is a clearest “tube” (muscular pharynx)
• The posterior opening of the pharynx is the mouth: the mouth is in the middle of the body, not at the anterior end
• It is a central mouth, meaning the opening is on the stomach
• The pharynx can be everted from the body and used to impale or pin food, which gets sucked into the mouth and then into the intestine
• Triclad (has three main trunks of intestine)
• The lone anterior trunk runs from the pharynx towards the head and the lower branches, the two posterior trunks, wrap around either side of the pharynx and run in the opposite direction
• Incomplete or blind gut (any waste products are ejected through the mouth)

Question 7

What is the excretion of planarians?

Answer 7

• A system of excretory canals and protonephridia is used in osmoregulation

Question 8

What is osmoregulation?

Answer 8

maintenance of water balance in the body

Question 9

What is the reproduction of planarians?

Answer 9

• Complex reproductive systems
• Monoecious and reproduce sexually (exchanging sex cells with other individuals)
• Or can be asexual (transverse fission)

Question 10

Explain the basics of the class Cestoda

Answer 10

• Tapeworms
• Parasitic flatworms
• Spend part of their lives in the intestines of mammalian hosts
• Have flat ribbon-like appearance
• Some can grow to lengths of over 30m long
• Their bodies can be divided into 3 main sections
  1) Strobila (ribbon-like body)
  2) Neck
  3) Scolex
• Strobila is made up of units called proglottids

Question 11

What is the nervous/sensory of tapeworms?

Answer 11

• Scolex contains cerebral ganglia

- Many tactile and chemoreceptors are present on the body

Question 12

What is the feeding/digestion of tapeworms?

Answer 12

• The scolex is equipped with round suckers and a rostellum containing hooks (these all help the animal adhere to the hosts intestines so it can feed)
• They have no intestines or digestive systems
• Each proglottid can absorb nutrients directly from the digested food in the intestine of the host

Question 13

What is the reproduction of tapeworms?

Answer 13

• Proglottids are formed by strobilation
• As new proglottids form at the neck, the older ones are pushed backwards
• The largest, most mature proglottids are at the posterior end and are filled with reproductive organs, including a pair of ovaries, many small testes and a genital pore
• After the eggs are fertilized, the proglottid swells as the uterus fills with embryos
• Gravid (swollen) proglottids eventually break off, and are shed in the hosts feces, which are later ingested by other animals, continuing the life cycle

Question 14

Explain the basics of the Phylum Nematoda

Answer 14

• Roundworms
• True body cavity (creates a space in which organs can develop and allows some freedom of movement within the body)
• Cavity is also often fluid filled, providing a hydrostatic skeleton for animals that lack a true skeleton
• This fluid facilitates the movement of oxygen to body cells; this is a more efficient way to obtain oxygen than the simple environment to cell diffusion seen in flatworms
• Many are parasitic, infecting the organs of humans and other animals
• Have sexual dimorphism (females are thicker and bigger than males)
• The body wall is covered with fluffy masses (these are muscle cells, which the animal uses to move its body from side to side)
• The body cavity is a pseudocoel (peritoneum does not cover the organs)

Question 15

What is the feeding/digestion of roundworms?

Answer 15

• The mouth empties into a short pharynx, which sucks food into the intestine
• Can be traced down to the anus
• Complete digestive system with both a mouth and an anus
• This means an animal can consume more food while the “old” food is still in the digestive tract, on its way out

Question 16

What is the reproduction of roundworms?

Answer 16

• The pseudocoel of female roundworms is filled with the reproductive system, which consists of a Y-shaped pair of 2 very long and convoluted tubes
• The base of the Y (closest to the anterior end) opens to the outside via the genital pore
• The thickest parts of the “arms” of the Y, closest to the pore are the two uteri
• The uteri narrow into oviducts, and eventually to hair-like ovaries
• The ovaries can contain up to 27 million eggs, which travel down the oviducts and into the uteri where fertilization occurs

Question 17

What is the male reproductive system of roundworms?

Answer 17

• Consists of only a single tube
• The thickest part of the tube, the seminal vesicle, is closest to the posterior end of the animal
• The tiny threadlike testis is at the opposite end, and the thicker vas deferens lies between the two
• Sperm made in the testis travel through the vas deferens, into the seminal vesicle and then are discharged through an ejaculatory duct that empties into the anus
• During mating, the male extends a pair of copulatory spicules from the anus to deposit sperm into the general pore of the female

Question 18

Explain the basics of the Phylum Mollusca

Answer 18

• Diverse Phylum
• Chitons, snails, slugs, clams, oysters, squids, octopuses, cuttlefish
• Triploblastic
• Display bilateral symmetry
• Cephalization
• Body cavity is a true coelom (completely lines with peritoneum)
• All major organ systems are present
• Occupy the land, sea and fresh water
• They fill different ecological niches as herbivores and as active predators

Question 19

What are some features that all molluscs share?

Answer 19

• A specialized, muscular foot
• A fold of dorsal body wall, called the mantle; this secretes a shell, and encloses the mantle cavity, which usually contains gills
• An open circulatory system with a heart
• A complete digestive system containing a mouth and an anus
• A well developed head
• A hardened shell

Question 20

What are the classes of the Phylum Mollusca?

Answer 20

Class Bivalvia
Class Gastropoda
Class Cephalopoda

Question 21

Explain the basics of the class bivalvia

Answer 21

• Freshwater mussel
• Include clams, oysters, mussels
• They live in fresh and salt water
• Able to move around on a substrate, but many spend a lot of time buried in sand or mud (where they filter the water for food)
• Lack a defined head
• Their nervous and sensory systems are quite simple, although the latter is better developed in the few bivalves (scallops, mostly) that have eyes

Question 22

What is the support in the freshwater mussels?

Answer 22

• The swollen hump on the dorsal side is the umbo. It is the oldest and thickest part of the valve
• Posterior end is longer than the anterior relative to the position of the umbo
• On dorsal side, you’ll also find the hinge ligament (this attaches the two valves and springs them open)
• The adductor muscles are the two muscles responsible for holding the shells closed
• The valves have a good defence. The hard shells deter many predators and provide a skeleton for muscle attachment. They also help keep mud and sand out of the mantle cavity

Question 23

Explain the valves in the freshwater mussels?

Answer 23

• Made up of three layers of calcium carbonate and protein formed from secretions from the mantle
• The inner layer has a mother of pearl sheen; this is the nacreous layer
• On the inner surface of the valve from which you removed the mantle, you should see a faint pallial line running along the circumference of the valve; this is where the pallial muscle, a component of the mantle, was once attached.

Question 24

What is the respiration in the freshwater mussels?

Answer 24

• Removing the mantle exposes the gills which are used in respiration
• The ridges and folds increase the surface area and maximize gas exchange
• Cilia on the mantle and gills keep water flowing in the mantle cavity
• Gills also act as a brood chamber for developing embryos in females; if the outer gill is much thicker than the inner its a female

Question 25

What is the movement/locomotion of the freshwater mussels?

Answer 25

• The firm, muscular foot is attached to the ventral surface of the visceral mass
• The foot is used for moving, digging and anchoring; it is extended/contracted via a combination of muscular action and blood flow
• Four foot muscles (anterior and posterior adductors and the anterior and posterior foot retractors

Question 26

What is the feeding/digestion of the freshwater mussels?

Answer 26

• The mouth is surrounded by two pairs of labial palps, which direct the food to the mouth
• The mouth leads to a short pharynx and then to the stomach, which is housed in the visceral mass
• The stomach is surrounded by greenish digestive glands
• The stomach narrows into coils of intestine that loop through the visceral mass, then connect to the rectum and anus, but first the intestine passes through the ventricle of the three-chambered heart, which lies in a small chamber beneath the pericardial membrane

Question 27

What is the circulation of the freshwater mussels?

Answer 27

• Bivalves have an open circulatory system, which means that the blood is not always contained in blood vessels
• It sometimes enters a body cavity (sinus) and simply bathes the organs with oxygenated blood
• From the visceral organs, blood is first carried to the kidney for removal of waste, then to the gills for gas exchange, then back to the heart, where it is pumped back out to the viscera

Question 28

What is the reproduction of the freshwater mussels?

Answer 28

• Much of the visceral mass is filled with a pale mass of gonads (dioecious)
• Sperm are released into the water and brought into the female via the incurrent siphon
• Embryos develop in the brood chamber, then are released into the water
• Larval bivalves bear hooks that let them attach to a passing fish; they live as parasites for several weeks before becoming bottom-dwelling, free-living adults
• The parasitic larval stage permits dispersal and provides a source of food

Question 29

Explain the basics to the class Gastropoda

Answer 29

• Land snails, whelks, abalone, slugs
• Largest group of molluscs
• Either one shell or no shell
• Found in water and on land
• Herbivores, omnivores, scavengers, carnivores or even parasitic
• Land snails are air breathers

Question 30

What is the support of the land snails?

Answer 30

• The “tip” of the snails shell (apex) is akin to the umbo of the bivalve shells: the apex is the oldest part of the shell
• Each complete spiral of the shell is a whorl
• The shell contains and protests the visceral mass and most of the mantle (therefore contains the digestive, cardiovascular and reproductive organs)

Question 31

What is the locomotion of the land snails?

Answer 31

• Like the bivalve, the snail possesses a muscular foot, which secretes a mucous which aids in locomotion

Question 32

What is the respiration/circulation of the land snails?

Answer 32

• Two openings on the mantle just beneath the edge of the shells aperture
• The hole closest to the head is the pneumostome (this allows air to enter a highly vascularized section of the mantle cavity)
• This acts as a “lung” where gas exchange takes place
• Snails have open circulatory system and a simple two chambered heart

Question 33

What is the sensory of the land snails?

Answer 33

• Snail has a distinct head that has two eyes perched atop eye stalks and two smaller tentacles used as tactile and chemoreceptive organs
• Their sensory and nervous systems are correspondingly more complex
• Most have reasonably well developed eye sight and extra nerve bundles in their tentacles

Question 34

What is the feeding/digestion of the land snails?

Answer 34

• The head also has a mouth
• The mouth is equipped with a series of sharp teeth on a rasping organ (the radula)
• This roughened surface helped provide some mechanical breakdown of food (a grinding action) before digestion
• Food travels from the mouth to the stomach to the intestine to the anus, which is the other opening on the mantle
• The snail has a digestive gland just like the bivalve

Question 35

What is the reproduction of the land snails?

Answer 35

• Most snails have both male and female gonads

- They are self fertilizing, probably because their slow movement makes it difficult to find a mate

Question 36

Explain the basics to the class Cephalopoda

Answer 36

• Squid, octopus, nautilus
• Free swimming predator animals
• Live and hunt in salt water
• Could be very tiny or huge
• Cephalopod means “head-foot”. The end of the head (bears the tentacles) is homologous to the ventral side of the bivalve; the tentacles are in fact a modified foot
• Well developed sensory and nervous system
• Excellent vision
• All have siphons (funnels)
• Some of the fastest cephalopod swimmers and are voracious hunters (squids)
• In Squids, the hard outer shell has been modified and reduced and has been replaced with a smaller internal structure called a pen, which is embedded the mantle

Question 37

What is the sensory of the squid?

Answer 37

• The head is at the ventral end
• Large complex eyes, which offer excellent visual acuity
• Their eyes evolved form completely different ancestral structures than our own, yet share a similar form and function (analogous traits)
• The skin has a mottled or spotted appearance (the darker spots are the chromatophores)

Question 38

What are chromatophores?

Answer 38

• Specialized pigment cells that allow the animal to rapidly change the colour of their skin
• Sweeping colour change are a complicated and highly developed means of communication and camouflage

Question 39

What is the locomotion of the squid?

Answer 39

• Body is long and streamlined (it is built for speed and mobility)
• The visceral mass (guts) is covered by a thick mantle
• The two fins (which provide propulsion and manoeuvrability) are at the dorsal end
• On the posterior side of the animal, emerging from under the mantle, is the tube-like siphon
• Water is forces from the siphon to create jet-propulsion

Question 40

What is the support of the squid?

Answer 40

• The mantle encloses the viscera
• The space between the mantle and the viscera is the mantle cavity
• Lying along the anterior side of the mantle, behind the visceral organs, is a rigid pen
• This is all that is left of the shell found in most other molluscs and it provides support; the loss of a shell means that the animals can be faster, more flexible and more manoeuvrable
• Firm cartilages in the head, funnel and mantle provide additional structural support

Question 41

What is the respiration/circulation of the squid?

Answer 41

• Two long, feathery gills are attached at one end to the visceral mass
• The gills are positioned in such a way so as to maximize water flow over them.
• Water is drawn into the mantle cavity via contraction/relaxation of the muscles in the mantle
• The heart and the branches of the main arteries and veins are all located at the point in the body where the gills attach
• The heart is actually composed of 3 sections (2 branchial hearts that supply blood to the gills and a central systematic heart that circulates blood to the rest of the body)

Question 42

What is the defense of the squid?

Answer 42

• The dark coloured ink sac is a prominent feature
• The squid can eject a cloud of ink through its siphon to startle or deter predators, and to create a kind of “smoke screen” while it escapes

Question 43

What is reproduction of the squid?

Answer 43

• The female has a prominent ovary at the dorsal end
• At the ventral end of the ovary is an oviductal gland, which secretes the shells of the eggs
• Lying between the gills of the female squid are two large nidamental glands (these are responsible for forming the outer capsules of egg masses)
• The oviduct is where eggs pass from the ovary to the siphon
• In the male, sperm passes through the coiled vas deferens, then to a whitish tube that runs towards the siphon (the penis)
• Sperm are discharged form the penis and collected bu finger like structures at the tip of the males modified arm
• The male uses this arm to transfer the sperm to a pouch in the females mantle
• The female uses one arm to pick up strings of her eggs as they pass through the oviduct and are ejected from her siphon; she then fertilizes them with the sperm she is storing in her pouch
• The egg masses are then attached to an object in the water for hatching

Question 44

What is the feeding/digestion of the squid?

Answer 44

• The head bears 10 appendages (8 shorter arms and 2 long tentacles)
• The muscular tentacles are adorned with suckers and can be rapidly shot out to capture prey
• The arms are used to draw prey into the mouth
• The mouth is guarded by a fierce looking beak made of chitin
• The stomach is above the heart, off to one side
• The caecum digests food after the bolus is passed on from the stomach
• The intestine starts at the stomach and terminates at the rectum; waste matter is passed through the siphon