Download ANSWERS TO REVIEW QUESTIONS – CHAPTER 40

ANSWERS TO REVIEW QUESTIONS – CHAPTER 40
1.
Briefly describe the structure and function of the water vascular system of a sea star. Which
echinoderms do not use tube feet for locomotion? (pp. 985–986 Figure 40.3)
The water vascular system is a derivative of the sea star coelom and its structure is shown in Figure
40.2. It is a system of canals and tube feet that exploits hydrostatic principles to aid in movement, as
well as assisting in gas exchange and excretion. The system opens to the outside through the
madreporite, located on the aboral (upper) surface of the sea star. This connects to the stone canal,
which descends to join the ring canal, which circles the mouth in the central body disk. Some species
have bulbous Pollian vesicles attached to the ring canal, probably acting as fluid reservoirs for the
system. A radial canal runs from the ring canal into each of the five arms, with a series of lateral canals
in each arm connecting the radial canal with the tube feet. Each tube foot is a hollow, muscular tube
with a bulbous ampulla at one end and often a sucker at the outer end. Suckers work most efficiently on
hard surfaces but are not effective on mud or silt.
During movement, valves in the lateral canals isolate each tube foot from the rest of the system. If a
valve is closed, fluid from the ampulla can be forced into the tube by muscular action to extend the
foot. Secretions on the surface help the tube foot to adhere, while further muscle contractions raise the
centre of the tube foot to create an adhesive vacuum. Considerable force can be exerted with this
system to enable the sea star to move, climb or dismember prey.
Tube feet are used in the locomotion of the classes Asteroidea, Ophiuroidea (but they are of limited
use, the arms do most of the work), Echinoidea (supplemented with the spines) and Holothuroidea
(with many species reducing the podia on the upper surface). The Crinoidea face their tube feet
upwards and use them for suspension feeding, trapping food particles and passing them along the
ambulacral grooves to the mouth.
2.
What type of symmetry is characteristic of echinoderms? Describe their skin and skeleton.
(pp. 986–987 Figure 40.5)
Radial symmetry. The internal skeleton is comprised of spicules or ossicles (plates) just beneath the
skin. Spicules are embedded beneath the skin where they may be single or fused together.
3.
What animals are characterised by pharyngeal gill slits? What functions do gill slits
perform? (p. 988 Figure 40.1)
Pharyngeal gill slits are paired openings in the pharynx appearing in deuterostomes called
Pharyngotremata at some stage of development. In ancestral forms they were used for feeding, being
the exits for water currents containing food moving through the mouth. Subsequent modifications have
adapted them for true gills in some species, while in others they are associated with hearing or
vocalisation.
4.
You find a sessile animal living in the intertidal zone of a marine habitat. A colleague
suggests that the animal is a tunicate. What features would you look for to determine that it
is a tunicate? (pp. 989–990 Figure 40.10)
Tunicates have several diagnostic features, including:
1.
2.
3.
4.
5.
6.
the body that is covered by a complex ‘tunic’ or coat containing a form of cellulose and lying
outside the epidermis
the pharynx that is perforated by many slits forms a basket for filter feeding
water flow for filter feeding, maintained by an incurrent siphon, which directs water through the
pharyngeal slits and out through an excurrent siphon
an endostyle or ciliated ventral groove in the pharynx that secretes mucus to aid in trapping food
particles
that most are hermaphrodite
that most are sessile as adults, although there are some free-living forms having the incurrent and
excurrent siphons at opposite ends of the body to aid in movement.
These features apply to the adults, not the larvae.
5.
What is the advantage of having jaws? Which cordates evolved jaws? What is the
evolutionary derivation of jaws—in other words, what are they homologous to? (pp. 991–
992 Figure 40.13)
The evolution of jaws enabled vertebrates to become predators, to increase their food base and attain a
wide range of body sizes. The earliest record of jawed vertebrates is the extinct armoured fish
(placoderms) and spiny fish (acanthodians) from the Silurian period. Jaws are derived from anterior
branchial arches of the gill system (refer to Figure 40.13).
6.
An anapsid skull is typical of turtles and their relatives. (pp. 997–998 Figure 40.22)
(a) What does ‘anapsid’ mean?
(b) In contrast, what is the term for the type of skull of lizards, crocodiles and birds and
what does it mean?
Anapsid and diapsid skulls are illustrated in Figure 40.20. The anapsid condition has been called ‘solidroofed’ by some authors and means that the skull lacks openings in the temples to accommodate the
jaw muscles. This structure is retained in modern turtles and their relatives. However, in most reptiles
one or two openings occur in the temple region on each side of the skull to allow freer movement of the
jaw muscles. This is known as the diapsid condition.
7.
Describe the features of birds that are associated with powerful flight. What features did the
early fossil bird Archaeopteryx have and why was it probably limited to fly only a short
distance? (pp. 998–1000 Figures 40.25–40.26)
Flight has been a driving evolutionary force in birds. Adaptations for flight centre on reducing weight
and improving blood supply to the flight muscles. They include:
1.
2.
3.
4.
5.
6.
7.
8.
forelimbs modified as wings
a body covering of feathers, which are modified reptilian scales; specialised wing and tail feathers
assist in flight, while all feathers assist in insulation, which helps in regulating body temperature
the sternum (breastbone) is keeled, giving a large surface area for attachment of the flight muscles
teeth that have been lost as a weight-reduction mechanism, with a horny bill used for feeding
endothermy which keeps the muscles constantly at a suitable temperature for flight
a four-chambered heart ensuring separation of oxygenated and deoxygenated blood in the
circulatory system for efficient supply of blood to the flight muscles
hollow, air-filled bones reinforced with struts to give strength while reducing weight
lungs which are augmented by an extensive system of air sacs that occupy much of the dorsal part
of the body. They allow unidirectional airflow through the lungs and the flow of air through this
extensive system may help dissipate the heat generated by muscular activity during flight. Gas
exchange in the lung itself exploits an efficient countercurrent system.
Archaeopteryx was very similar to theropod dinosaurs. It had teeth, claws on its forelimbs and a long
tail with vertebrae—it is only the presence of feathers that show the link with birds. In the absence of
other specialised features, it is unlikely that it flew long distances.
8.
What features are unique and characteristic of mammals? Name the three main groups of
mammals and explain how you would identify a representative of each. (pp. 1001–1002)
Mammalian characteristics include:
1.
2.
3.
4.
5.
6.
hair as a body covering*
milk secretion for the nourishment of the young*
presence of a diaphragm used in respiration between the thoracic and abdominal cavities*
a lower jaw of single pair of bones*
three bones in each middle ear connecting the eardrum and the inner ear*
in most forms, young born alive and in the embryonic stage, nourished within the mother via a
placenta (viviparous development)
7. teeth differentiated into incisors, canines, premolars and molars, each specialised for specific
functions
8. a four-chambered heart
9. endothermy, permitting activity across a wide range of temperatures and climates
10. a greatly enlarged brain, especially in the cerebral hemispheres.
Points marked * are unique to mammals, while the others are characteristic but can occur in other
groups.
Features of the three main groups of mammals are given below.
Monotremes
Egg-laying mammals, with shell
glands in the female reproductive
tract
Metatheria
Young are nourished from the
uterine wall via a yolk-sac
placenta
Eutheria
Young are nourished in the uterus
via a chorioallantoic placenta,
formed from extra-embryonic
membranes of the developing
young and the uterine wall
Mammary glands lack nipples
Two separate uteri with two
distinct lateral vaginas and a
bifurcate penis
Uteri may be separate or fused,
but there is only one vagina
Functional teeth absent in adults
Young born at a very early stage
of development
Penis not bifurcated
Oviducts open into a cloacal
chamber
Young normally concealed and
carried in a pouch
Penis anterior to the scrotum
Two separate uteri (females) and
bifurcate penis (males)
Penis posterior to the scrotum
No scrotum in males
Horny spur on the ankle of males,
may be grooved for the passage
of poison
Bones of the pectoral girdle
similar to those in reptiles
9.
Primates are classified into two groups. What are these two groups and what are their
characteristic features? Give examples of each group. (pp. 1002–1004 Figures 40.31–40.32)
Strepsirhini—naked nose pad, slit-like nostrils, nasal prominences unfused e.g. lemurs.
Haplorhini—do not have a rhinarium, but rather have a nose with rounded nostrils e.g. humans.
10. How does the skeleton of australopithecines and other hominids differ from that of the
gorilla? (pp. 1005–1007 Figure 40.36)
The important differences are illustrated in Figure 40.36.
One suite of changes is associated with the evolution of bipedalism. In comparison to a gorilla, the
australopithecine and hominid lines have shortened the pelvis, developed an ‘S’ shape to the spine and
placed the head above the spinal column. In humans the arms are also shortened relative to the legs,
which contrasts with the gorilla, where the arms are longer than the legs. Humans also have the big toe
as the longest digit on the foot.
A second suite of changes is associated with the skull. The brain case in australopithecines and
hominids has enlarged steadily, with an associated reduction in the size of the jaws relative to the
overall size of the skull.