30
The Animal Kingdom: The Deuterostomes
Lecture Outline
I.
Echinoderms are characterized by their water vascular system
A. All members of phylum Echinodermata are marine
1. They are found in intertidal areas, and are among the most abundant
benthic organisms in the abyssal sea
a) They may be classified into 6 major groups
b) Today they represent maximum diversity in the early Cambrian
period, with about 2,000 extant and 13,000 extinct species
c) Most have a complete digestive system
2. Echinoderms are secondarily radially symmetrical (pentaradial), as their
larvae are bilateral
3. Echinoderms have an endoskeleton, as their calcareous plates are covered
with an epidermis
4. Many have pincerlike pedicellariae, unique tools used to keep their surface
clean of debris
5. The water vascular system and tube feet are unique to this phylum
6. Echinoderms have a well-developed coelom, various respiratory
structures, and no excretory organs
7. The nervous system consists of a nerve net
8. Echinoderms are dioecious and fertilization is typically external
B. Members of class Crinoidea are suspension feeders
1. This group includes the feather stars and sea lilies
2. The crinoids are the most ancient class, and relatively few extant species
exist
a) Their oral surface is located on the upper side of the disc
3. Feather stars are motile; sea lilies are sessile and stalked
4. The crinoids are suspension feeders
C. Many members of class Asteroidea capture slow moving prey
1. This class includes the sea stars
2. Sea stars have 5 or more arms with tube feet on the undersurface
3. In order to eat clams or barnacles, they grasp the valves with their tube feet
and arms to force them open; they then slide the food into the stomach and
start to dig
4. Dermal gills function in respiration
5. The coelomic fluid aids in circulation
D. Class Ophiuroidea is the largest class of echinoderms
1. This group includes basket stars and brittle stars
2.
The ophiuroids have arms that are distinctly set off from the central disc
and are much more flexible; they have tube feet without suckers
E.
Members of class Echinoidea have moveable spines
1. This group includes sea urchins and sand dollars (echinoids)
2. Echinoids lack arms, but have tube feet and pedicellaria
3. Sea urchins are grazers
4. Sand dollars feed on organic matter in the sand
F. Members of class Holothuroidea are elongated, sluggish animals
1. This class includes sea cucumbers, which are benthic
2. The sea cucumbers have reduced skeletons and few tube feet
3. Sea cucumbers often eviscerate internal organs when bothered or when
environmental conditions are unfavorable
G. Members of class Concentricycloidea have a unique water vascular system
1. The sea daisies were first discovered in 1986 in deep ocean waters
II.
Chordate characters include a notochord, dorsal tubular nerve cord, pharyngeal
slits, and post anal nail during some time in the life cycle
A. Members of phylum Chordata are divided into three subphyla, two
invertebrates and one vertebrate
1. Chordates are coelomates with bilateral symmetry, an endoskeleton, and a
closed circulatory system with a ventral heart
2. Chordates have a notochord at some time in the life history
a) The notochord is a flexible supporting rod
3. Chordates have a single dorsal tubular (hollow) nerve cord
4. All chordates have pharyngeal gill slits—in some, only in the embryo
a) In the ancestral chordates, the gill slits allowed suspension feeding
b) In fish, gills allow respiration, and feeding in some species
c) Anterior pharyngeal arches evolved into jaws early in vertebrate
evolution
5. Most chordates have a muscular postanal tail
a) Nonchordates have an inverted anus that ends at the terminus of the
tail
B. Tunicates are common marine animals
1. Subphylum Urochordata includes the tunicates or ascidians
2. The sea squirts (class Ascidiacea) and relatives like the salps are tunicates
3. Tunicates are typically sessile as adults and are covered with a tunic made
of a polysaccharide similar to cellulose
a) The tunic forms an incurrent and excurrent siphon
b) Sea squirts feed as suspension feeders and trap food particles in the
pharynx
4. Larval tunicates have all typical chordate characteristics
5. Adult sea squirts lose most of the typical chordate characteristics
6. Some are colonial, sharing common tunic and excurrent siphon, and
reproduce by budding
7. Sexual forms are usually hermaphroditic
C.
Lancelets may be closely related to vertebrates
1. Subphylum Cephalochordata includes the lancelets
2. The lancelets are small fish-like animals found free-swimming or buried in
the sand
3. Branchiostoma (amphioxus) is a common genus of lancelet
4. All 4 chordate characteristics are highly developed
5. Recent molecular evidence shows that these animals are the vertebrates'
closest living relatives
D. Chordate phylogeny is controversial
1. Fossil evidence is scanty
2. Yunnanozoan fossils from China (early Cambrian) are well preserved; though soft
bodied, they may represent an early deuterostome, not a chordate; others do think it
was a chordate
3. The Burgess Shale Pikaia fossil is an early cephalochordate
E. The success of the vertebrates is linked to the evolution of key adaptations
1. Members of subphylum Vertebrata have a vertebral column
a) A vertebral column is composed of vertebrae made of bone or cartilage
b) A cranium is located at the anterior end of the vertebral column
2. The endoskeleton of vertebrates is living and grows with the animal
3. Pronounced cephalization marks the vertebrates
4. Vertebrates have two pairs of appendages (or evolved from organisms that
had them), a closed circulatory system with a ventral heart, paired kidneys,
and a complete digestive tract with large digestive glands
5. Vertebrates are far less diverse and numerous than the insects, but have
much more complex behaviors
6. Vertebrates may be divided into 3 classes of fishes (superclass Pisces) and 4
classes of terrestrial vertebrates (superclass Tetrapoda)
F. The jawless fish are the earliest vertebrates
1. Members of class Agnatha include the extinct ostracoderms and the extant
lampreys and hagfishes (although systematists may divide this group into
two extant classes)
2. These first vertebrates evolved in the sea about 450 to 500 mya
a) The ostracoderms radiated greatly and were primarily freshwater
fishes
3. The lampreys and hagfishes are scaleless, elongate fish without jaws or
paired fins
4. Hagfish are marine scavengers
5. Lampreys are found in freshwater or marine habitats and include
ectoparasitic species
a) Adult lampreys leave the ocean or lake and swim to a stream to spawn
G. The earliest jawed fishes are now extinct
1. In the late Silurian period, jawed fish evolved from freshwater
ostracoderms
2.
The acanthodians and the placoderms were the first two groups of jawed
fish
a) The jaw developed from a gill support and enabled fish to become
effective predators
H. Members of class Chondrichthyes are cartilaginous fishes
1. Class Chondrichthyes includes the sharks, rays, and skates, and evolved in
marine habitats during the Devonian period
2. Sharks and their relatives have paired fins and placoid scales
3. The teeth of sharks are constantly replaced
4. The largest sharks are filter feeders (whale and basking sharks)
5. Well developed sense organs allow most sharks to be efficient predators
a) Electroreceptors on the head and the lateral line running down the
side of the body allow them to sense prey
6. Chondrichthyean fish have 5-7 pairs of gills, and most rely on swimming
to force water over their gills
7. The digestive, reproductive, and excretory systems are typical of
vertebrates
a) The digestive tract and urinary tracts empty into the cloacae
b) The male has a specialized pelvic fin with a clasper, which is an
intermittent organ
c) Sharks may be oviparous, ovoviviparous, or viviparous
I. Members of class Osteichthyes are bony fishes
1. The bony fish are the most speciose of the vertebrate classes
a) The bony fish appeared in the fossil record during the Devonian
period
b) The skeleton of osteichthyean fish is made of bone, and the body is
covered with overlapping flexible scales
c) Bony fish are typically oviparous and produce a prodigious number of
eggs, which are fertilized externally
2. The ray-finned fishes gave rise to modern bony fishes
a) The ray-finned fishes (class Actinopterygii), the lobe-finned fishes
(class Actinistia), and the lungfishes (class Dipnoi) may be
distinguished
b) The ray-finned fishes evolved into several groups that are now nearly
extinct, and one group, the teleosts, which are the most speciose group
of fish
c) The lungs of the ray-finned fish's ancestor evolved to form a swim
bladder
3. Descendants of the lobe-finned fishes moved onto the land
a) The lungfishes and lobe-finned fishes diverged from the ancestral
sarcopterygian
b) Lungs were advantageous during the droughts during the Devonian
c)
The lungfishes are found today in river systems in Africa, Australia,
and South America
d) The lobe-finned fishes are survived only by the coelacanth (Latimeria),
found off the coast of Africa
J. Amphibians were the first successful land vertebrates
1. Class Amphibia includes frogs, toads, and salamanders
2.
The first amphibians, the labrinthodonts, evolved from the lobe-finned
fishes
a) The labrinthodonts were the first tetrapods and evolved during the
Carboniferous period
b) The labrinthodonts gave rise to the amphibians as well as the
cotylosaurs—early reptiles
3. Members of order Urodela include the salamanders and newts, which have
tails and most resemble the ancestral amphibian
4. Members of order Anura lack tails and include toads and frogs
5. Members of order Apoda include the legless tropical caecilians
6. The larvae of frogs and toads are aquatic, herbivorous tadpoles
a) Metamorphosis of the tadpole involves many morphological and
biochemical changes, and is triggered by thyroxine
b) Some salamanders do not undergo metamorphosis and become
mature while still in a larval form, called neoteny
7. Adult amphibians rely heavily on cutaneous respiration
8. The amphibian heart has 3 chambers (2 atria and 1 ventricle)
a) Pulmonary and systemic circulation are partially separated
K. Reptiles were once the dominant land animals
1. Class Reptilia includes turtles, lizards, snakes, and alligators
2. Reptiles are typically terrestrial and do not rely on water to reproduce
a) The development of the amniotic egg was an important evolutionary
development
b) The amniotic egg contains the amnion, which surrounds the embryo
and other membranous sacs
3. Reptiles were once the dominant land animals
a) The earliest reptiles diverged into the group that led to the mammals,
the turtles, and the group that gave rise to all other extant reptiles, the
dinosaurs, and the birds
b) More extinct than extant species of reptiles exist
c) The dinosaurs and other reptiles dominated during the Mesozoic era
d) At the end of the Mesozoic, the dinosaurs and half of all living animal
species became extinct
e) Many reptilian characters are adaptations to terrestrial life
(1) The bodies of reptiles are covered by dry scales, which prevent
cutaneous respiration
(2) The lungs of reptiles are more efficient than that of amphibians,
and the ventricle of the heart has a partial (or complete) partition
(3) Wastes are excreted in the form of uric acid, which reduces water
loss
(4) Reptiles are ectothermic, as are fishes and amphibians
(5) The majority of reptiles are carnivorous
f)
Modern reptiles belong to three orders
(1) Members of order Chelonia include the turtles, terrapins, and
tortoises and are covered with a bony shell, and may be found in
marine, freshwater, and terrestrial habitats
(2) Members of order Squamata include the lizards and snakes
(a) This is the most speciose order of reptiles
(b) Snakes evolved from tetrapods, but have many unusual
adaptations for efficient predation, including chemical and
temperature senses, and toxins
(3) Members of order Crocodilia include the crocodiles, alligators,
gavials and caimans
(a) Crocodiles are the largest extant reptiles, growing up to 7
m in length
L. Are birds really dinosaurs?
1. Cladistics indicate birds evolved from saurischian dinosaurs
M. Modern birds are adapted for flight
1. The birds belong to class Aves
2. Early birds had reptilian characteristics
a) Birds evolved from saurischian dinosaurs
b) Archaeopteryx is an early genus of bird and exhibits characteristics of
both modern birds and reptiles
c) Birds may be characterized by the possession of feathers, which
evolved from the scales of reptiles
3. Modern birds are a very successful group
a) The anterior appendages of birds are wings, and most birds fly
b) Adaptations for flight include skeletal reduction, efficient lungs
including air sacs, a 4-chambered heart, endothermy, and frequent
voiding of wastes
c) To maintain a high metabolic rate, birds typically eat high energy
foods
d) The nervous system is well developed, and senses such as sight and
hearing are keen
e) Complex social behavior, vocalizations, territoriality etc. are hallmarks
of the birds
f) Many birds make long migrations
N. Mammals are characterized by hair and mammary glands
1. Members of class Mammalia are characterized by specializations in
dentition, a diaphragm to aid in respiration, endothermy, and a 4chambered heart
a) The nervous system, particularly the cerebrum, is quite advanced in
the mammals
b) Fertilization is always internal, and nearly all mammals are viviparous
c) Most mammals are placental
d)
The limbs of mammals show adaptations for diverse forms of
locomotion
2.
3.
Early mammals were small, endothermic animals
a) Mammals evolved from reptiles, the therapsids, during the Triassic
period
b) The early mammals were arboreal and nocturnal, avoiding contact
with the ruling reptiles
c) After the Mesozoic, the mammals underwent extensive adaptive
radiation, filling "empty" niches
Modern mammals are assigned to three subclasses
a) These three subclasses had evolved by the end of the Cretaceous
period
b) Monotremes are mammals that lay eggs
(1) Members of subclass Prototheria include the duck-billed platypus
and the spiny anteater (echidna)
(2) When the young hatch, they are fed with milk from the mammary
glands
c) Marsupials are pouched mammals
(1) Members of subclass Metatheria include kangaroos, koalas, and
opossums and are most common in Australia
(2) Marsupials exhibit parallel evolution with the eutherian mammals
d) Placental mammals complete embryonic development within the
mother
(1) Members of subclass Eutheria are the most common mammals
and form a placental connection between the embryo and the
mother in the uterus
Research and Discussion Topics

Why might it be advantageous for sea stars and brittle stars to be able to regenerate
arms? Hint: Think about where they live.

Why are the largest sharks, the whale and basking sharks, filter feeders? What are
the organisms involved in this rather short, polar food chain? Are the largest whales
also filter feeders or predators?

Investigate the interesting historical story of the discovery of the first specimen of a
living coelacanth off the coast of South Africa. What is the meaning of the generic
(genus) name, Latimeria? Where have more specimens been found, and what has
been learned about the morphology and behavior of this "living fossil"?

Research the wide variety of reproductive strategies seen in anurans. The interesting
mouth brooding frog, which was discovered in 1973, became extinct in 1980. Where
else do anurans brood the eggs and larvae? Resource: Duellman, W.E.
"Reproductive Strategies of Frogs." Scientific American. July 1992. 80-87.

What has been the contribution of Xenopus laevis (the African "clawed" frog) to
research? Why is its distribution to teaching and research institutions so restricted?

Assess the various theories concerning the extinction of the dinosaurs and other
Mesozoic reptiles. Which has the most geological and biological supporting
evidence?

Define the terms endothermic, ectothermic, poikilothermic, and homeothermic.
How does each of these terms apply to the organisms studied in this chapter? Which
of these is the most energetically expensive? What are some current theories
concerning the thermoregulation of the dinosaurs? It is often said that lizards are
"heliotherms." What might that mean?

List at least 10 adaptations seen in birds that facilitate flight. Include adaptations
seen in the digestive, excretory, reproductive, skeletal, and nervous systems.

Discuss the different theories about the development of flight and feathers in birds.
What purpose may the first feathers have served?