1. What are the most important features of animals?

Animals
are multicellular, eukaryotic organisms lacking cell walls. They are
heterotrophic, consuming organic material for energy. Animals
develop through a characteristic process, including stages such as
blastula and gastrula, and most have complex tissues organized
into organs. Most reproduce sexually, are diploid, and exhibit
varying degrees of mobility, adapting to diverse environments.
2. Why are Choanoflagellates considered the most likely
common ancestor of all animals? Choanoflagellates are similar
to the collar cells (choanocytes) found in sponges, one of the
simplest animals. Molecular evidence supports that
choanoflagellate-like organisms are the closest living relatives of
animals, sharing similarities in feeding mechanisms and cell
structure.
3. Describe five key innovations in the evolution of animals.
 Symmetry: From asymmetry (sponges) to radial symmetry
(cnidarians) to bilateral symmetry (most animals), enabling more
complex movement and organ distribution.
 Tissues: Differentiation into true tissues allowed for specialization,
seen in most animals except sponges.
 Body Cavity (Coelom): This allowed for organ development and
body structure flexibility, seen in coelomates like arthropods.
 Segmentation: Enabled redundancy and mobility, particularly in
annelids and arthropods.
 Developmental Patterns: Divergence into protostomes (mouth
forms first) and deuterostomes (anus forms first), leading to varied
evolutionary lineages.

4. Animals may differ in the number of layers of cells they

show during their embryonic development. How many layers
of cells can you find? Animals may have two (diploblastic, like
cnidarians) or three (triploblastic, like most animals) germ layers.
Diploblastic animals have ectoderm and endoderm, while
triploblastic animals also have mesoderm, allowing for complex
organs and body cavities.
5. Describe the body plan of Porifera. Explain how sponges
feed. Porifera (sponges) have a simple body plan with no true
tissues, organized into a porous body wall. Water enters through
pores into a central cavity, the spongocoel, and exits via the
 osculum. Choanocytes (collar cells) use their flagella to create water
currents, trapping food particles in mucus which are engulfed by
phagocytosis.
6. What is the basic body plan of cnidarians? What are
nematocysts and how do they function? Cnidarians have a
diploblastic, radially symmetrical body with a gastrovascular cavity,
and they exist in two forms: sessile polyps and free-floating
medusae. Nematocysts are specialized stinging cells that eject a
barbed thread to capture prey or for defense, injecting toxins into
targets.
7. What are the benefits of developing a body cavity? A body
cavity, or coelom, provides a space for organs to develop and grow
independently from the body wall, allows for a larger and more
complex digestive system, protects internal organs, and facilitates
better movement and flexibility.
8. What are the main characteristics of the Phylum Nematoda?
Nematodes are unsegmented, cylindrical worms with a complete
digestive tract and a body covered by a cuticle. They have no
circulatory system and are often parasitic, thriving in diverse
environments.
9. What are the main differences between Protostomes and
Deuterostomes? In protostomes, the mouth forms from the
blastopore, while in deuterostomes, the blastopore becomes the
anus. Protostomes exhibit spiral cleavage and determinate cell fate,
whereas deuterostomes have radial cleavage and indeterminate cell
fate.
10. What are the benefits of a closed circulatory system? A
closed circulatory system allows for efficient nutrient and gas
exchange, rapid transport of oxygen, and waste removal. Blood
remains separate from bodily fluids, enhancing control and pressure
in larger or more active animals.
11. What are some unique features of Mollusca? Molluscs have
a soft body typically covered by a hard calcium carbonate shell.
Their body is divided into three main parts: the muscular foot (for
movement), the visceral mass (containing most internal organs),
and the mantle (a tissue layer that may secrete the shell). Molluscs
also often possess a radula, a unique rasping organ used to scrape
food.
12. What is the importance of the mantle? The mantle is a
significant structure in mollusks. It secretes the shell in species that
 have one and forms a cavity that houses organs like gills and
excretory pores. In some species, the mantle cavity also facilitates
respiration.
13. How do mollusks move? Mollusks use their muscular foot for
movement, which varies across species. For example, gastropods
(like snails) glide using the foot, while cephalopods (like squids) use
a jet propulsion system, expelling water through a siphon for rapid
movement.
14. Name the four main groups of Mollusca. What are their
main characteristics?
 Polyplacophora (Chitons): Oval-shaped with eight dorsal
plates, clinging tightly to rocks and feeding by scraping algae.
 Gastropoda (Snails and Slugs): Have a single, usually
spiraled shell (or none in slugs), with many species adapted to
terrestrial life.
 Bivalvia (Clams, Oysters): Characterized by a shell divided
into two hinged parts; most are filter feeders.
 Cephalopoda (Squids, Octopuses): Predatory mollusks with
tentacles, a highly developed nervous system, and a closed
circulatory system.
15. What are the benefits of a segmented body? A segmented
body provides flexibility, allowing each segment to move
independently and supporting complex movements. It also enables
redundancy of organs, enhancing survival if one segment is injured.
16. Explain how nudibranchs or sea slugs protect themselves
from predation. Nudibranchs can defend themselves by storing
stinging cells from prey (like cnidarians) within their own tissues,
using these stinging cells for defense. Some also release noxious
chemicals or display bright warning colors to deter predators.
17. If Annelids lack gills, how do they respire? Annelids like
earthworms use their skin for respiration. Their skin must remain
moist to facilitate gas exchange, allowing oxygen to diffuse into
their body while expelling carbon dioxide.
18. What are the main classes of Annelida? Annelida is divided
into two main clades:
 Errantia: Primarily marine, mobile annelids with parapodia and
often well-developed jaws.
 Sedentaria: Less mobile, including tube-dwelling worms and
earthworms, adapted for burrowing or a sessile lifestyle.
19. Describe the body plan of earthworms. Earthworms have a
segmented body with a true coelom that houses organs, divided by
septa. Their body contains a continuous digestive tract, blood
vessels, and nerve cords. Each segment contains structures like
nephridia for excretion, and chaetae, or bristles, aid in locomotion.
20. What are the main characteristics of the Phylum
Arthropoda? Arthropods are characterized by a segmented body,
exoskeleton made of chitin, jointed appendages, and well-
developed sensory organs. They exhibit a high degree of
specialization in body parts, aiding in functions such as movement,
feeding, and sensory reception.
21. What are the traits that allow the separation of the
different classes of Arthropoda?
The primary traits include body segmentation, appendage
specialization, and mouthparts. For example:
 Insects have a three-part body (head, thorax, abdomen) with
three pairs of legs and, usually, wings.
 Crustaceans have two main body regions (cephalothorax and
abdomen), two pairs of antennae, and appendages on both body
sections.
 Arachnids have two main body segments (cephalothorax and
abdomen), eight legs, and no antennae.
 Myriapods (centipedes and millipedes) have many body
segments, each with one or two pairs of legs.
22. Name animals that belong to each of the four classes of
Arthropoda.
 Insects: Butterflies, ants, beetles
 Crustaceans: Crabs, lobsters, shrimp
 Arachnids: Spiders, scorpions, ticks
 Myriapods: Centipedes and millipedes.
23. Describe the circulatory system of arthropods. Arthropods
have an open circulatory system in which hemolymph (a fluid
analogous to blood) is pumped by the heart into sinuses (body
cavities) surrounding organs. Hemolymph bathes the organs
directly and reenters the heart through pores after circulating
through the body.
24. What is the difference between the compound eyes and
the ocelli?
 Compound eyes are composed of multiple units called
ommatidia, each functioning as an individual visual receptor,
 providing a broad field of vision and detecting movement
effectively.
 Ocelli (simple eyes) are small and detect light intensity rather
than detailed images, helping with orientation and regulating
circadian rhythms.
25. Compare the body plan of insects, crustaceans,
arachnids, and myriapods.
 Insects: Three body sections (head, thorax, abdomen), three
pairs of legs, and often wings.
 Crustaceans: Two main regions (cephalothorax and abdomen),
with two pairs of antennae and numerous specialized
appendages for various functions.
 Arachnids: Two main body sections (cephalothorax and
abdomen), four pairs of legs, and chelicerae for feeding.
 Myriapods: Many body segments, each segment with legs (one
pair per segment in centipedes, two pairs in millipedes).
26. Why is the variation in the mouthparts of insects so
important? The variation in mouthparts allows insects to exploit
diverse ecological niches and feed on a wide range of resources,
from solid food (e.g., chewing in grasshoppers) to liquid food (e.g.,
sucking in butterflies and piercing in mosquitoes). This diversity in
feeding mechanisms supports their adaptability and evolutionary
success.
27. Describe the feeding habits of the different classes in this
phylum.
 Insects: Varied, including herbivores, carnivores, detritivores,
and parasitic feeders.
 Crustaceans: Mostly scavengers, filter feeders, or predators.
 Arachnids: Primarily carnivorous, using venomous fangs to
immobilize prey (e.g., spiders) or specialized mouthparts to suck
fluids (e.g., ticks).
 Myriapods: Centipedes are predators, while millipedes are
mostly detritivores, feeding on decomposing plant material.
28. How do insects form their wings? Insect wings are
extensions of the cuticle that develop as outgrowths of the thoracic
body wall. They typically grow from the second and third thoracic
segments and are supported by a network of veins that provide
structure and flexibility.
29. What characteristics are common to all classes of phylum
Echinodermata? All echinoderms have radial symmetry (usually
 five-fold) as adults, an internal skeleton made of calcareous plates,
and a unique water vascular system used for movement and
feeding. They also possess tube feet operated by hydraulic
pressure.
30. What is a unique feature of this phylum? Echinoderms have
a water vascular system, a network of hydraulic canals branching
into tube feet, which enables them to move, feed, and exchange
gases. This system is unique to echinoderms and a defining trait of
the phylum.
31. Describe the body plan of this group.
Echinoderms, the group being referenced here, have a body plan
that includes radial symmetry as adults (typically five-part
symmetry), an internal skeleton made of calcium carbonate plates
(ossicles), and a water vascular system that powers their tube feet,
aiding in movement and feeding. Their body structure is organized
around a central disc, and they have no head or brain.
32. How can you differentiate among individuals of different
classes in this phylum?
Echinoderm classes differ mainly in body shape and specific
structures:
 Asteroidea (sea stars): Have five arms and a central disc, with
tube feet on the underside of the arms.
 Ophiuroidea (brittle stars): Similar to sea stars but with
slender, flexible arms and distinct central discs.
 Echinoidea (sea urchins and sand dollars): Lack arms, have
a round or flattened body with spines, and a rigid skeleton.
 Holothuroidea (sea cucumbers): Soft-bodied, elongated, with
tube feet arranged in rows, and reduced skeleton.
 Crinoidea (feather stars and sea lilies): Sessile or free-
swimming with feather-like arms.
33. What are the four features that characterize the phylum
Chordata?
The four defining features of chordates are:
 Notochord: A flexible, rod-like structure providing support.
 Dorsal, hollow nerve cord: Runs along the back and develops
into the central nervous system.
 Pharyngeal slits or clefts: Openings near the throat that
function in feeding or respiration.
 Post-anal tail: An extension of the body past the anus, used in
movement in some chordates.
34. How can you separate among different subphyla of
Chordata?
The subphyla of Chordata are distinguished by unique traits and
developmental features:
 Cephalochordata (lancelets): Retain all four chordate features
throughout life.
 Urochordata (tunicates): Larvae display all chordate features,
but adults are sessile and mainly retain pharyngeal slits.
 Vertebrata: Characterized by a well-defined head, a backbone
or vertebral column replacing the notochord, and a more
complex nervous system.
35. In which subphylum does the notochord persist
throughout the life of the animal?
The notochord persists throughout life in the subphylum
Cephalochordata (e.g., lancelets), providing structural support as
they lack a vertebral column.
36. What are the main characteristics of the subphylum
Vertebrata?
Vertebrates have a backbone that replaces the notochord during
development, a well-defined head with a brain enclosed in a skull,
paired sensory organs, and an advanced nervous system.
Vertebrates also have an endoskeleton that supports the body and
allows for movement.
37. What are the major groups of fish? How can you
distinguish them?
Fish are divided into three main groups:
 Agnatha (jawless fish): Includes hagfish and lampreys; lack
jaws and paired fins.
 Chondrichthyes (cartilaginous fish): Includes sharks, rays,
and skates; have a skeleton made of cartilage, exposed gill slits,
and usually lack a swim bladder.
 Osteichthyes (bony fish): Characterized by a bony skeleton,
gill covers (operculum), and a swim bladder for buoyancy.
38. What is the origin of the jaw?
Jaws are thought to have evolved from the modification of skeletal
rods that once supported the gills in early jawless fish, providing the
ability to grasp and process larger prey.
39. How do fish respire? How is respiration different in sharks
versus bony fish?
Fish respire by extracting oxygen from water through their gills:
  Sharks (Chondrichthyes): Use ram ventilation, where water
flows over the gills as they swim, or they actively pump water
using mouth muscles. They often lack a swim bladder, so some
need constant movement to respire efficiently.
 Bony fish (Osteichthyes): Use an operculum that covers the
gills, allowing them to pump water over the gills even when
stationary, a method more efficient for sedentary or slower-
moving lifestyles.
40. What is the lateral line system? In what groups is it
present?
The lateral line system is a sensory organ in fish and some
amphibians that detects water currents, vibrations, and pressure
changes, helping in navigation, predator detection, and prey
location. It is composed of mechanoreceptors along the sides of the
body, and it’s present in both cartilaginous and bony fish.
41. How do bony fish control their buoyancy?
Bony fish control their buoyancy using a swim bladder, a gas-filled
sac that can adjust the fish's buoyancy in water. By varying the
amount of gas (usually oxygen) in the swim bladder, they can float
at different depths without expending energy on constant
swimming.
42. Bony fish can be separated into two major groups. What
are the names of those groups? What traits allow this
separation?
The two major groups of bony fish are:
 Actinopterygii (ray-finned fish): Have fins supported by long,
flexible rays and are the most common group of fish.
 Sarcopterygii (lobe-finned fish): Have fleshy, lobed fins with
a robust internal skeleton, which is thought to be an ancestral
trait leading to the evolution of tetrapods.
43. Explain how vertebrates made the transition from aquatic
to terrestrial life.
Vertebrates transitioned to land by developing adaptations such as
limbs for movement on solid ground, lungs for breathing air, and
structural changes to support their body weight against gravity.
Ancestors of amphibians, such as certain lobe-finned fish, possessed
robust bones in their fins that allowed them to support themselves
in shallow waters, eventually leading to fully terrestrial adaptations.
44. Describe the traits that amphibians have that allowed
them to use land habitats.
 Amphibians developed lungs to breathe air, limbs to support
movement on land, and a partially divided heart to improve
circulation. Their moist skin allows gas exchange, supplementing
their lungs. However, they typically require moist environments or
water for reproduction and early development due to their aquatic
larval stage.
45. What are the three key characteristics shared by all
reptiles?
 Scales or a similar keratinized covering that helps prevent water
loss.
 Internal fertilization, allowing them to reproduce without
water.
 Amniotic eggs with protective shells, enabling embryos to
develop in a self-contained environment on land.
46. Describe the structure of the amniotic egg. How is it
different from the egg of an amphibian?
The amniotic egg has a shell and several membranes (amnion,
chorion, allantois, and yolk sac) that protect the embryo, manage
waste, and provide nutrients and oxygen. Unlike amphibian eggs,
which lack a shell and are typically laid in water, the amniotic egg
can be laid on land due to its protective shell and specialized
membranes, which prevent desiccation.
47. Compare the circulatory system of the different groups of
Vertebrata.
 Fish: Have a single-loop circulatory system with a two-
chambered heart.
 Amphibians: Possess a double-loop system with a three-
chambered heart (two atria and one ventricle), allowing partial
separation of oxygenated and deoxygenated blood.
 Reptiles (except crocodiles): Have an incomplete double-loop
system with a partially divided ventricle, enhancing oxygenated
blood flow but allowing some mixing.
 Crocodilians, Birds, and Mammals: Have a four-chambered
heart, with complete separation of oxygenated and
deoxygenated blood, allowing for more efficient oxygen
transport.
48. What are the distinct characteristics of birds?
Birds are characterized by feathers, a lightweight but strong
skeletal structure with hollow bones, a beak with no teeth, and high
metabolic rates. They have a four-chambered heart and efficient
 respiratory systems, including air sacs, to support flight. Birds are
also endothermic, maintaining a constant body temperature.
49. What groups of vertebrata are endothermic?
Birds and mammals are endothermic, meaning they generate heat
internally and maintain a stable body temperature, which allows
them to inhabit diverse and colder environments.
50. What are the distinct characteristics of mammals?
Mammals have mammary glands that produce milk, hair or fur for
insulation, a four-chambered heart, and a diaphragm to aid in
breathing. They also exhibit advanced brain development and
differentiated teeth suited for varied diets. Most mammals give live
birth (except monotremes, which lay eggs).
51. Explain how the morphology of teeth is related to diet in
mammals.
Mammalian teeth are highly specialized and adapted to their diets:
 Carnivores (e.g., cats, dogs) have sharp, pointed canines and
premolars for tearing flesh, as well as strong jaws for gripping
prey.
 Herbivores (e.g., deer, horses) possess broad, flat molars and
premolars designed for grinding plant material, as well as
smaller or absent canines.
 Omnivores (e.g., humans, bears) have a combination of sharp
canines for tearing and flat molars for grinding, allowing them to
process both plant and animal matter effectively. This dental
specialization supports efficient food processing, reflecting
dietary habits and aiding in nutrient absorption.
52. There are three main groups of mammals; how can you
distinguish them?
The three main groups of mammals are:
 Monotremes: Egg-laying mammals (e.g., platypus and echidna),
which lay eggs with leathery shells and lack nipples; the young
feed on milk secreted from mammary glands onto the mother’s
skin.
 Marsupials: Pouched mammals (e.g., kangaroos, koalas) that
give birth to live young at an early developmental stage; the
newborns crawl into the mother’s pouch, where they continue to
develop and nurse.
 Eutherians (Placental mammals): Have a complex placenta
that nourishes the embryo during a longer gestation period,
 allowing for more developed young at birth (e.g., humans,
elephants).
53. Compare the reproduction of all groups of vertebrata,
considering fertilization, embryo, and development.
 Fish: Generally exhibit external fertilization, where eggs and
sperm are released into the water. Most fish undergo external
development as well, though some have internal fertilization with
live birth (e.g., sharks).
 Amphibians: Mostly reproduce with external fertilization in
water, and embryos develop into larvae (tadpoles) that undergo
metamorphosis. Some amphibians have adaptations for
terrestrial egg-laying, but development is still largely external.
 Reptiles: Typically exhibit internal fertilization, and most lay
eggs with leathery shells for terrestrial development. Some
reptiles are ovoviviparous or viviparous, with live births.
 Birds: Have internal fertilization, lay hard-shelled eggs, and
embryos develop externally. Birds incubate their eggs until
hatching, which often requires parental care.
 Mammals:
a. Monotremes lay eggs that develop externally.
b. Marsupials have internal fertilization and give birth to
underdeveloped young that continue development in a pouch.
c. Eutherians (placental mammals) have internal fertilization
and gestate within the mother’s uterus, supported by a
complex placenta.

Terminology

 Radial symmetry: Symmetry around a central axis, as seen in

organisms like jellyfish, where body parts radiate out from the
center.
 Bilateral symmetry: A type of symmetry where the body has
distinct left and right halves that mirror each other, common in
animals like humans.
 Cephalization: The concentration of sensory organs and nervous
tissue at the anterior (front) end of an organism, leading to the
formation of a head.
 Osculum: A large opening in sponges through which water flows
out after circulating through the body.
 Choanocyte: Also called collar cells, these are flagellated cells in
sponges that create water currents and trap food particles.
 Amoebocyte: Mobile cells within sponges that distribute nutrients
and aid in structural support by producing spicules and spongin.
 Endoderm: The innermost germ layer in an embryo, which
develops into the digestive tract and associated organs.
 Mesoderm: The middle germ layer in an embryo, giving rise to
muscles, bones, and the circulatory system in triploblastic animals.
 Ectoderm: The outermost germ layer in an embryo, which develops
into the skin and nervous system.
 Mesoglea: The gelatinous layer between the ectoderm and
endoderm in cnidarians like jellyfish.
 Gastrodermis: The inner layer of cells in cnidarians that lines the
gastrovascular cavity, aiding in digestion.
 Acoelomates: Animals without a body cavity between the digestive
tract and outer body wall (e.g., flatworms).
 Pseudocoelom: A fluid-filled body cavity between the mesoderm
and endoderm, seen in nematodes.
 Coelom: A true body cavity completely lined with mesoderm, found
in most complex animals.
 Flame cells: Specialized cells in flatworms that function in
excretion and osmoregulation by filtering wastes from the body.
 Turbellaria: A class of mostly free-living flatworms, known for their
regenerative abilities and commonly found in freshwater
environments.
 Trematoda: A class of parasitic flatworms, also called flukes, which
often have complex life cycles involving multiple hosts.
 Cercaria: A larval stage of some parasitic flatworms (trematodes)
that can penetrate hosts to complete their life cycle.
 Miracidium: A free-swimming ciliated larval stage of certain
parasitic flatworms (trematodes) that infects the initial host,
typically a snail.
 Osculum: An opening at the top of a sponge where water exits
after circulating through the sponge’s body.
 Mesohyl: The gelatinous matrix within sponges that contains cells
involved in nutrient transport and structural support.
 Gastrodermis: The tissue lining the gastrovascular cavity in
cnidarians, aiding in digestion and nutrient distribution.
 Polyp: The sessile, cylindrical body form of cnidarians (e.g., sea
anemones) that attaches to surfaces.
 Medusa: The free-swimming, bell-shaped body form of cnidarians,
seen in organisms like jellyfish.
 Planula: The free-swimming, ciliated larval stage of cnidarians,
which eventually settles to develop into a polyp.
 Anthozoa: A class of cnidarians that includes sea anemones and
corals, characterized by a polyp-only life stage.
 Hydrozoa: A class of cnidarians that includes species like Hydra
and Portuguese man o' war, often with both polyp and medusa
stages.
 Scyphozoa: A class of cnidarians that includes the true jellyfish,
predominantly in the medusa form.
 Scolex: The head region of a tapeworm, containing hooks and/or
suckers for attachment to the host’s intestine.
 Proglottid: A segment in a tapeworm containing reproductive
organs; mature proglottids break off to spread eggs.
 Rotifera: A phylum of tiny aquatic animals with a wheel-like crown
of cilia used for feeding and locomotion.
 Determinate development: A type of embryonic development in
which the fate of each cell is fixed early, typical of protostomes.
 Indeterminate development: A type of embryonic development
in which each cell has the potential to develop into a complete
organism, typical of deuterostomes.