Biology 102 Chapter 32
Animal Origins and Lophotrochozoans
1. List characteristics that distinguish animals from other
organisms in the other four kingdoms.
---multicellular, eukaryotic organisms
---heterotrophy is by ingestion
--ingestion = eating other organisms or decomposing
organic matter (detritus)
-this mode of nutrition distinguishes animals from the
plants and fungi
--carbohydrate reserves are stored as glycogen
---NO cell walls present
--are intercellular junctions, desmosomes, gap junctions
and tight junctions
---highly differentiated body cells organized into tissues,
organs, and organ systems
--specialized functions such as digestion, internal
transport, gas exchange, movement, coordination,
excretion, and reproduction
---nervous tissue (impulse conduction) and muscle tissue
(movement) unique to animals
---reproduction is typically sexual with flagellated sperm
fertilizing nonmotile eggs to form diploid zygotes
--diploid stage dominates life cycle
---zygote undergoes series of mitotic divisions known
as cleavage which forms a blastula in most animals
---gastrulation occurs after blastula formed; during
this process, embryonic forms of adult body tissues
produced
---development in some animals is direct to maturation
--others include larva which undergo metamorphosis
into sexually mature adults
-larva = free-living, sexually immature forms
2. Outline and describe the major phylogenetic branches of the
animal kingdom, which are based upon grade of organization;
symmetry and embryonic germ layers; absence or presence of a
body cavity; and protostome-deuterostome dichotomy.
---entire structure of an animal, its organ systems, and
integrated functioning of its parts known as its BODY PLAN
---ancestral protist-->multicellularity-->
---sponges, cnidarians, and ctenophores separated early from
remaining animal lineages
---remaining animals divided into two major lineages
--protostomes and deuterostomes
---(1) no true tissues (Parazoa) and true tissues
(Eumetazoa)
---(2) radial symmetry, diploblastic (Radiata) and
bilateral symmetry, triploblastic (Bilateria)
---(3) no body cavities (Acoelomates) and body cavities
---body cavity not enclosed by mesoderm (Pseudocoelomates)
and body cavity enclosed by mesoderm (Coelomates)
---(4) coelom from cell masses (Protostomes) and
coelom from digestive tube (Deuterostomes)
BODY SYMMETRY
---symmetrical animal can be divided along at least ONE PLANE
into similar halves
---asymmetrical animals have no plane of symmetry
--sponges
---spherical symmetry designates animals in which body parts
radiate out from a central point
--infinite number of planes passing through the central
point can divide organism into similar halves
--widespread among protists
---radial symmetry designates animals that have one main axis
around which body parts are arranged
--perfectly radially symmetrical animal can be divided
into similar halves by any plane that contains main axis
--have oral (top) and aboral (bottom) side, but no front,
back, left, or right sides
--some sponges, sea anemones
---biradial symmetry designates radially symmetrical animals
modified such that only TWO planes, at right angles to
each other can divide them into similar halves
--Cnidaria, Ctenophora, and Echinodermata
---bilateral symmetry designates animal that can be divided
into mirror images by only ONE plane that passes through
midline of body from front to back
have dorsal (top), ventral (bottom), anterior (head),
posterior (tail), left and right body surfaces
--exhibit cephalization (an evolutionary trend toward
[] of sensory structures at anterior end
EMBRYONIC GERM LAYERS
---diploblastic animals have only TWO cell layers
--outer ectoderm and inner endoderm
---triploblastic animal have third layer called mesoderm
--mesoderm lies between ectoderm and endoderm
BODY CAVITIES
---fluid-filled spaces that lie between the cell layers of body
---type of body cavity strongly influences how animal can move
---acoelomate = an animal body plan characterized by NO body
cavity present between the digestive tract and outer body wall
--area between digestive tract and outer wall is filled with
cells, producing a solid body
---do not have a blood vascular system
---psuedocoelomate = animal body plan characterized by a fluidfilled body cavity that separates the digestive tract and the
outer body wall
--this cavity (pseudocoelom) is NOT completely lined with
tissue derived from mesoderm
---coelomate = animal body characterized by a fluid-filled body
cavity completely lined with tissue derived from mesoderm
(the coelom) that separates the digestive tract from the
outer body wall
--mesenteries connect inner and outer mesoderm layers &
suspend the internal organs in the coelom
--these fluid-filled body cavities
-cushion the organs, preventing injury
-allow internal organs to grow & move independently of
the outer body wall
-serve as hydrostatic skeleton in soft-bodied coelomates
such as earthworms
SPIRAL/RADIAL CLEAVAGE
---radial cleavage = cells divide along plane parallel to or
at right angles to long axis of fertilized egg
--pattern persisted in deuterostomes and many protostome
lineages
---spiral cleavage = plane of cell division is oblique to long
axis of egg causing cells to be arranged in spiral pattern
DETERMINATE/INDETERMINATE CLEAVAGE
---determinate cleavage = egg allowed to divide few times and
cells are separated, each cell develops into only PARTIAL
embryo (protostomes)
---indeterminate cleavage = cells separated after several
divisions can still develop into COMPLETE embryos
(deuterostomes)
SCHIZOCOELOUS/ENTEROCOELOUS
---schizocoelous formation of coelom = solid masses of mesoderm
split to form coelom (mollusks, annelids, arthropods, and
other phyla)
---enterocoelous formation of coelom = folds of archenteron form
coelom; mesoderm buds form wall of archenteron and hollow to
become coelomic cavities (Echinodermata and Chordata)
---protostomes have spiral cleavage
---deuterostomes have radial cleavage
---protostomes have determinate cleavage
---deuterostomes have indeterminate cleavage
---protostomes have blastopore forming the mouth
---deuterostomes have blastopore forming the anus
---protostomes have schizocoelous coelom formation
---deuterostomes have enterocoelous coelom formation
3. From a diagram, identify the parts of a sponge and describe
the function of each including the spongocoel, porocyte,
epidermis, choanocyte, mesophyll, amoebocyte, osculum, and
spicule.
---spongocoel = central cavity of sponge
---osculum = larger excurrent opening of spongocoel
---epidermis = single layer of flattened cells which forms
outer surface of sponge
---porocyte = cells which form pores; possess hollow
channel through the center which extends from outer
surface (incurrent pore) to spongocoel
---choanocyte = collar cell, majority of cells which line
spongocoel; possess flagellum ringed by collar of
fingerlike projections
---mesophyll = jellylike layer located between the two
layers of sponge body wall (epidermis/choanocytes)
---amoebocyte = wandering, pseudopod bearing cells in
mesohyl; function in food uptake from choanocytes;
food digestion, nutrient distribution to other cells,
formation of skeletal fibers, gamete formation
---spicule = sharp, calcium carbonate or silica structures
in the mesohyl which form skeletal fibers of many
sponges
---spongin = flexible, proteinaceous skeletal fibers in
mesohyl of some sponges
4. List the characteristics of the phylum Cnidaria and phylum
Ctenophora that distinguish them from the other animal phyla.
PHYLUM CNIDARIA
---radial symmetry
---diploblastic
---simple, sac-like body
---gastrovascular cavity is small central digestive
cavity with only one opening (functions as mouth
and anus)
---cnidocytes are specialized cells of epidermis that
contain eversible capsule-like organelles called
cnidae that are used in defense/capture of prey
---Cnidarians have two basic body plans
---polyp = cylindrical form which adheres to substratum
by aboral end of body stalk and extends tentacles around
oral end to contact prey
---medusa = flattened, oral opening down, bell-shaped form;
moves freely through water by passive drifting & weak
bell contractions; tentacles dangle from oral surface
which points downward
PHYLUM CTENOPHORA
---also known as comb jellies
---radial symmetry; diploblastic; feeding tentacles
---ctenophores have a complete gut (mouth and 2 anal pores)
---have 8 comblike rows of fused plates of cilia called
ctenes
---tentacles do NOT have nematocysts
--covered with sticky filaments to which prey adhere
---all are marine carnivores
5. List characteristics that are shared by all bilaterally
symmetrical animals.
---possesses dorsal and ventral side; anterior and
posterior end; left and right side; and cephalization
---move actively from place to place
---have array of intercellular signaling systems and many
homeobox gene families
6. Describe the structural characteristics of a
lophotrochozoan.
---triploblastic
---grow by adding to the size of their skeletal elements
---use cilia for locomotion
---many lineages have free-living larva known as trochophore
---contains 9 phyla
7. List the characteristics of the phylum Platyhelminthes that
distinguish it from the other animal phyla.
---are dorsoventrally flattened acoelomates
---exhibit bilateral symmetry with moderate cephalization
---possess several distinct organs, organ systems, and
true muscles
---gastrovascular cavity is present
---Turbellaria (planarians); Cestoda (tapeworms); Trematoda
(flukes); Monogenea (monogeneans)
8. List the characteristics of the plylum Annelida that
distinguish it from the other animal phyla.
---segmented body resembling series of fused rings
is hallmark of annelid worms
--separate nerve center (ganglion) controls each segment
--coelom in each segment isolated from those in other
segments
---five pairs of hearts
---excretory system of paired metanephridia found in
each segment
--each metanephridia has a nephrostome (which removes
wastes from coelomic fluid and blood)
---thin body wall serves as surface for gas exchange but
restricts to moist environments
9. List the characteristics that distinguish the phylum Mollusca
for the other animal phyla.
---have muscular foot, visceral mass, and a mantle
---all mollusks are soft-bodied but most protected by
calcium carbonate shell
10. Describe the basic body plan of a mollusk and explain how it
has been modified in the Gastropoda, Bivalvia, and Cephalopoda.
---body consists of muscular foot (locomotion), visceral
mass (contains most internal organs), and a mantle
(heavy fold of tissue surrounding visceral mass and
secretes the shell, if present)
---Gastropoda (snails/slugs) undegoes torsion during
embryonic development (anus above the head)
---shell (except in slugs/nudibranchs) that is conical
or flattened
---Bivalvia (clams/oysters/mussels/scallops) possess
shell divided into two halves
---Cephalopoda (squids/octopuses) are agile carnivores
--shell is reduced, internal, or completely absent
--mantle modified (exit siphon) to forcibly eject water
from cavity allows rapid movement through water
--cephalopods are only mollusks with closed circulatory
system; blood always contained within vessels
11. Distinguish among the following four Molluscan classes and
give examples of each:
a. Gastropoda
c. Cephalopoda
b. Bivalvia
d. Polyphacophora
GASTROPODA
---Gastropoda contains the snails and slugs
--largest molluscan class
--torsion during embryonic development
--body protected by conical or flattened shell
-shell absent in slugs/nudibranchs
--most are herbivorous
--movement by rippling motion along elongated foot
BIVALVIA
---Bivalvia contains the clams, oysters, mussels, and
scallops
--possess shell divided into two halves
--most are suspension feeders
--lead sedentary lives
CEPHALOPODA
---Cephalopoda contains the squids and octopuses
--agile carnivores
--shell is reduced, internal, or absent
--only mollusks with closed circulatory system
POLYPLACOPHORA
---Polyplacophora contains the chitons
--have multiple gills
--oval shape with shell divided into 8 dorsal plates