BIO 104 4/25/96
I. Introduction
A. Evolutionary origin of animals
1. all of the major animal groups evolved in the ocean during the
Cambrian period (590-505 million years ago)
2. all of the animal phyla contain aquatic members
3. only three groups: arthropods, mollusks, and vertebrates have
terrestrial members
B. problems associated with terrestrial existence
1. water loss
2. external fertilization versus internal fertilization
3. external embryonic development versus internal embryonic
development
4. regulation of body temperature
II. Characteristics of animals
A. all members of the Kingdom Animalia are eukaryotic and multicellular
B. all animals are heterotrophic (must ingest their food)
1. animals must be able to locate food
2. some animals have evolved complex mechanisms for attracting prey
(food)
C. all animals are mobile at some point in their development
1. in sessile animals (which do not move -- sponges, for example),
the larval forms are mobile
2. movement requires the development of specialized cells -- muscle
cells; in some animals these cells are grouped into tissues which
accomplish specialized movement
3. movement necessitates the ability to respond to changes in the
environment -- nervous system
D. since animals are heterotrophic -- all animals must have the means to
digest their food in some kind of "gut"
E. animals must have a mechanism for moving food absorbed from the gut
throughout the body to the body cells
F. similarly, animals must be able to circulate oxygen to all of the body
cells and collect the carbon dioxide which is a by-product of cellular
metabolism
G. animals exchange gases between their bodies and the atmosphere -- some
animals have specialized structures for gas exchange -- gills (fishes),
spiracles (insects), and lungs (vertebrates), or an equivalent
structure
H. animals have developed structures to rid their bodies of waste products
--flame cells in the Planaria to kidneys in vertebrates
I. animals must be able to maintain a homeostatic balance for all of
their body cells (water balance, pH, etc)
J. animals undergo sexual reproduction -- gametic meiosis
1. some animals have both male and female reproductive structures in
the same body -- monoecious or hermaphroditic (such as tapeworms
and flukes)
2. some animals have separate sexes -- dioecious (nematodes and
insects, for example)
NOTE: Approximately 90% of the different animal species are invertebrates.
III. Classification of animal groups
A. classification is based on similarities in internal structure &
embryonic development
B. this method of classification assumes a common ancestor based on common
morphology (shape) - homology
C. DNA analysis allows scientists to give more precise estimates of
relatedness (see Chapter 25 -- Sidelight 25.1, pp 482-483 in Raven &
Johnson)
D. characteristics used in the classification of animals
1. cells
a. unicellular - Kingdom Protista
b. multicellular - Kingdom Animalia
2. type of body symmetry (refer to Figure 29.8, p 548 in Raven &
Johnson)
a. asymmetrical -- sponges
b. radial symmetry -- cnidaria
c. bilateral symmetry -- flatworms
3. number of embryonic germ layers
a. none -- protists
b. two -- diploblastic cnidarians
c. three -- triploblastic flatworms, nematodes, annelids, etc
4. type of digestive cavity
a. incomplete -- one opening (mouth and anus are the same
opening) -- example: Planaria
b. complete -- two openings (separate mouth and anus) -- example:
earthworm
5. type of embryonic development -- fate of the blastopore (refer to
Figure 29.2, p 545 in Raven & Johnson)
a. protostome
1. blastopore becomes the mouth
2. spiral determinant cleavage
3. trochophore larva
b. deuterostome
1. blastopore becomes the anus
2. radial indeterminate cleavage
3. dipleural larva
6. type of internal body cavity (refer to Figure 29.9, p 549 in Raven &
Johnson)
a. acoelomate (no internal body cavity present -- flatworms)
b. pseudocoelomate (internal body cavity between the endoderm
and the mesoderm; usually fluid-filled to serve as a
hydrostatic skeleton -- round worms [nematodes])
c. coelomate (internal body cavity derived from and surrounded
by mesoderm -- echinoderms & chordates)
(1). provides an internal space for body organs
(2). allows for internal fertilization and gestation of
young
7. skeleton -- external or internal
8. nerve cord -- dorsal or ventral
IV. Evolutionary Advances
Primitive Characteristic Advanced Characteristic
unicellular multicellular
radial symmetry bilateral symmetry
diploblastic triploblastic
incomplete digestive tract complete digestive tract
protostome deuterostome
no internal body cavity body cavity lined with mesoderm
no head region cephalization
IV. Sponges: Phylum Porifera (refer to pp 544-546; Figures 29.3 & 29.4, p 546; and
Figures 29.6 & 29.7, p 547 in Raven & Johnson)
A. represent an evolutionary dead end
B. basic features
1. sessile -- do not move as adults; larvae are free-swimming
2. water-filtering systems
3. common on ocean floors
4. asymmetrical body plan
C. more than colonial; less than multicellular
1. cells not organized into tissues or organs (refer to Figure 29.3,
p 546 in Raven & Johnson)
2. have some specialized cells
(a).collar cells - choanocytes
(b).epithelial cells
(c).amoebocytes -- for feeding
3. digestion of food occurs in individual cells
4. support
(a). spongin -- protein; commercial sponges are processed so
that the spongin remains intact
(b). spicules -- calcium carbonate, silicon dioxide -- tiny
needle-like structures which serve a support function and
deter predators
D. reproduction
1. commonly asexual
2. mostly hermaphrodites