Chapter 32 - An Overview of Animal Diversity

anterior

Pertaining to the front, or head, of a bilaterally symmetrical animal.

POSTERIOR

Pertaining to the rear, or tail end, of a bilaterally symmetrical animal.

Dorsal

Pertaining to the top of an animal with radial or bilateral symmetry.

Ventral

Pertaining to the underside, or bottom, of an animal with radial or bilateral symmetry.

A bilateral animal has two axes of orientation:

front to back and top to bottom.

bilaterians include ...

molluscs, arthropods, chordates, and most other living animal phyla.

Animal life cycle

- Although some animals, including humans, develop directly into adults, the life cycles of most animals include at least one larval stage. - . Animal larvae eventually undergo metamorphosis

Neoproterozoic Era (1 Billion-542 Million Years Ago)

- Animals first evolved in the Neoproterozoic era, and while steroid biomarkers provide the earliest evidence in this era - the first generally accepted macroscopic fossils of animals date from 565 to 550 million years ago - These fossils are members of an early group of soft-bodied multicellular eukaryotes, known collectively as the Ediacaran biota

Paleozoic Era (542-251 Million Years Ago)

- Cambrian explosion - the oldest fossils of about half of all extant animal phyla, including the first arthropods, chordates, and echinoderms - Many of these distinctive fossils, which include the first animals with hard, mineralized skeletons, look very different from most living animals - most of the fossils from the Cambrian explosion are of bilaterians - Vertebrates (fishes) emerged as the top predators of the marine food web. By 460 million years ago, groups that diversified during the Cambrian period were making an impact on land. Arthropods began to adapt to terrestrial habitats

In all other animals, the embryo becomes layered through the process of gastrulation. As development progresses, these layers, called germ layers, form the various tissues and organs of the body They are?

- Ectoderm, the germ layer covering the surface of the embryo, gives rise to the outer covering of the animal and, in some phyla, to the central nervous system. - Endoderm, the innermost germ layer, lines the pouch that forms during gastrulation (the archenteron) and gives rise to the lining of the digestive tract (or cavity) and organs such as the liver and lungs of vertebrates.

A body cavity has many functions...

- Its fluid cushions suspended organs - prevent internal injury. -In soft-bodied coelomates, ie. earthworms, coelom contains noncompressible fluid that acts like a skeleton against which muscles can work. - enables the internal organs to grow and move independently of the outer body wall. If it were not for your coelom, for example, every beat of your heart or ripple of your intestine would warp your body's surface.

Sexual reproduction in animals

- a small, flagellated sperm fertilizes a larger, nonmotile egg, forming a diploid zygote. - The zygote undergoes cleavage. - cleavage leads to the formation of a multicellular stage called a blastula - takes the form of a hollow ball - Following the blastula stage is the process of gastrulation, during which the layers of embryonic tissues that will develop into adult body parts are produced. - The resulting developmental stage is called a gastrula

As the diversity of animal phyla increased during the Cambrian period, the diversity of Ediacaran life-forms declined. What caused these trends?

- during the Cambrian period, predators acquired novel adaptations, such as forms of locomotion that helped them catch prey, while prey species acquired new defences, such as protective shells. As new predator-prey relationships emerged, natural selection may have led to the decline of some groups and the rise of others - Another hypothesis focuses on an increase in atmospheric oxygen that preceded the Cambrian explosion. More plentiful oxygen would have enabled animals with higher metabolic rates and larger body sizes to thrive, while potentially harming other species. -- A third hypothesis proposes that the origin of Hox genes and the addition of new microRNAs (small RNAs involved in gene regulation) facilitated the evolution of new body forms.

rangeomorphs

- sessile - characterized by fractal (self-similar) branching patterns - This unique pattern makes them difficult to classify, as they do not seem to be closely related to any living animal or algal groups. Rangeomorphs are, however, found in deep-water sediments where light would be limiting, thus indicating they were likely heterotrophic. Rangeomorphs disappeared from the fossil record in the Paleozoic era.

Cenozoic Era (65.5 Million Years Ago to the Present)

-Mass extinctions of animals ushered the Cenozoic. - nonflying dinosaurs and the marine reptiles disappeared. -large mammalian herbivores and predators as mammals began to exploit the vacated ecological niches. -The global climate cooled triggering significant shifts in many animal lineages. -Among primates, for example, some species in Africa adapted to the open woodlands and savannas that replaced many of the former dense forests. The ancestors of our own species were among those grassland apes.

Mesozoic Era (251-65.5 Million Years Ago)

-first coral reefs - new habitats formed - some reptiles returned to water - descent with modification on land, led to some tetrapods developing wings (birds and pterosaurus) - dinosaurs appeared - first mammals - nocturnal insect-eaters appeared - angiosperms and bugs diversified

Hemichordates

-share some characteristics with chordates, such as gill slits and a dorsal nerve cord; -echinoderms lack these characteristics. -These shared traits may have been present in the common ancestor of the deuterostome clade (and lost in the echinoderm lineage). -phylum Chordata, the only phylum with vertebrate members, also includes invertebrates like tunicates that possess a dorsal notochord.

Protostome development cleaveage

-spiral cleavage: the planes of cell division are diagonal to the vertical axis of the embryo -the determinate cleavage of some animals with protostome development rigidly casts ("determines") the developmental fate of each embryonic cell very early. A cell isolated from a snail at the four-cell stage, for example, cannot develop into a whole animal. Instead, after repeated divisions, such a cell will form an inviable embryo that lacks many parts.

The Diversification of Animals

1. All animals share a common ancestor. 2. Sponges are basal animals. 3. Eumetazoa is a clade of animals with true tissues. 4. Most animal phyla belong to the clade Bilateria. 5. There are three major clades of bilaterian animals.

What are the three lines of evidence that choanoflagellates are closely related to animals?

1. morphologically the choanoflagellatescells and other collar cells (or choanocytes) of sponges are almost indistinguishable 2. similar collar cells have been seen in other animals i.e. cnidarians, flatworms and echinoderms - BUT they have NEVER been observed in nonchoanoflagellate protists or in plants/fungi 3. DNA sequence data suggest that choanaflagellates and animals are sister groups. ALSO genes for signalling and adhesion proteins previously known only from animals have been found in choanoflagellates

one recent molecular clock study estimated that sponges originated about _____million years ago. These findings are also consistent with molecular analyses suggesting that the common ancestor of all extant animal species lived about 770 million years ago

700

Coelom

A body cavity lined by tissue derived only from mesoderm. A so-called "true" coelom forms from tissue derived from mesoderm. The inner and outer layers of tissue that surround the cavity connect and form structures that suspend the internal organs. Animals with a true coelom are known as coelomates

metamorphosis

A developmental transformation that turns an animal larva into either an adult or an adult-like stage that is not yet sexually mature.

body cavity

A fluid- or air-filled space between the digestive tract and the body wall.

larva

A free-living, sexually immature form in some animal life cycles that may differ from the adult animal in morphology, nutrition, and habitat.

Cambrian explosion

A relatively brief time in geologic history when many present-day phyla of animals first appeared in the fossil record. This burst of evolutionary change occurred about 535-525 million years ago and saw the emergence of the first large, hard-bodied animals.

ARE ACOELOMATE FLATWORMS BASAL BILATERIANS?

A series of recent molecular papers have indicated that acoelomate flatworms (phylum Acoela) are basal bilaterians, as shown in Figure 32.11. A different conclusion was supported by a 2011 analysis, which placed acoelomates within Deuterostomia If further evidence supports this hypothesis, this would suggest that the bilaterians may have descended from a common ancestor that resembled living acoelomate flatworms—that is, from an ancestor that had a simple nervous system, a saclike gut with a single opening (the "mouth"), and no excretory system.

Acoelomate

A solid-bodied animal lacking a cavity between the gut and outer body wall. some triplobastic animals lack a body cavity altogether

indeterminate cleavage

A type of embryonic development in deuterostomes in which each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo.

radial cleavage

A type of embryonic development in deuterostomes in which the planes of cell division that transform the zygote into a ball of cells are either parallel or perpendicular to the vertical axis of the embryo, thereby aligning tiers of cells one above the other.

spiral cleavage

A type of embryonic development in protostomes in which the planes of cell division that transform the zygote into a ball of cells are diagonal to the vertical axis of the embryo. As a result, the cells of each tier sit in the grooves between cells of adjacent tiers.

determinate cleavage

A type of embryonic development in protostomes that rigidly casts the developmental fate of each embryonic cell very early.

fate of blastopore

After the archenteron develops, in most animals a second opening forms at the opposite end of the gastrula. In many species, the blastopore and this second opening become the two openings of the digestive tube: the mouth and the anus.

EUMETAZOA IS A CLADE OF ANIMALS WITH TRUE TISSUES.

All animals except for sponges and a few others belong to a clade of eumetazoans ("true animals"). True tissues evolved in the common ancestor of living eumetazoans. Basal eumetazoans, which include the phyla Ctenophora (comb jellies) and Cnidaria, are diploblastic and generally have radial symmetry.

How do genes control animal development?

All animals have developmental genes encoding transcription factors that regulate the expression of other genes, and many of these regulatory genes contain sets of DNA sequences called homeoboxes`

SPONGES ARE BASAL ANIMALS.

Among the extant taxa, sponges (phylum Porifera) branch from the base of the animal tree. Recent morphological and molecular analyses indicate that sponges are monophyletic, as shown here.

Ediacaran biota

An early group of soft-bodied, multicellular eukaryotes known from fossils that range in age from 565 million to 550 million years old.

cephalization

An evolutionary trend toward the concentration of sensory equipment at the anterior end of the body.

Insects and plants have been in a co-evolutionary arms race for millions of years.

Another clue is seen in fossilized fern galls—enlarged cavities that fern plants form in response to stimulation by resident insects, which then use the galls for protection. Fossils indicate that fern galls date back at least 302 million years, suggesting that insects and plants were influencing each other's evolution by that time.

MOST ANIMAL PHYLA BELONG TO THE CLADE BILATERIA.

Bilateral symmetry and the presence of three germ layers are shared derived characters that help define the clade Bilateria. This clade contains the majority of animal phyla, and its members are known as bilaterians. The Cambrian explosion was primarily a rapid diversification of bilaterians.

THERE ARE THREE MAJOR CLADES OF BILATERIAN ANIMALS

Bilaterians have diversified into three main lineages, Deuterostomia, Lophotrochozoa, and Ecdysozoa. With one exception, the phyla in these clades consist entirely of invertebrates, animals that lack a backbone; Chordata is the only phylum that includes vertebrates, animals with a backbone.

Bilateral Symmetry

Body symmetry in which a central longitudinal plane divides the body into two equal but opposite halves.

ALL ANIMALS SHARE A COMMON ANCESTOR.

Current evidence indicates that animals are monophyletic, forming a clade called Metazoa. All extant and extinct animal lineages have descended from a common ancestor.

Coelom Formation Deuterstome vs protostome

During gastrulation, an embryo's developing digestive tube initially forms as a blind pouch (a cavity closed at one end), the archenteron, which becomes the gut Protostome: As the archenteron forms, the solid masses of mesoderm cells split to form the fluid-filled cavity, the coelom. Deuterostome development: the mesoderm buds from the wall of the archenteron, and its cavity becomes the coelom.

Deuterostomia

Echinodermata and Chordata One of the three main lineages of bilaterian animals.

______________________helps to explain why most animals are not a hollow ball of cells.

Gastrulation

Grade

Groups that share biological traits not derived from the same ancestor form

Diploblastic

Having two germ layers.

Why would coelomates and pseudocoelomates not form a clade?

However, phylogenetic studies show that true coeloms and pseudocoeloms have been independently gained or lost multiple times in the course of evolution; thus, they did not inherit these traits from a common ancestor and would not form an evolutionary clade (a group that includes an ancestral species and all of its descendants).

Blastospore

In a gastrula, the opening of the archenteron that typically develops into the anus in deuterostomes and the mouth in protostomes.

deuterostome development

In animals, a developmental mode distinguished by the development of the anus from the blastopore; often also characterized by radial cleavage and by the body cavity forming as outpockets of mesodermal tissue.

protostome development

In animals, a developmental mode distinguished by the development of the mouth from the blastopore; -spiral cleavage -body cavity forming when solid masses of mesoderm split.

What is a true tissue

In animals, true tissues are collections of specialized cells isolated from other tissues by membranous layers.

lophophore

In some lophotrochozoan animals, including brachiopods, a crown of ciliated tentacles that surround the mouth and function in feeding.

ARE CTENOPHORES BASAL METAZOANS?

Many researchers have concluded that sponges are basal metazoans However, several recent studies have placed the comb jellies (phylum Ctenophora) at the base of the animal tree. Data that are consistent with placing sponges at the base of the animal tree include fossil steroid evidence, molecular clock analyses, the morphological similarity of sponge collar cells to the cells of choanoflagellates and the fact that sponges are one of the few animal groups that lack true tissues (as might be expected for basal animals). Ctenophores, on the other hand, have true tissues and their cells do not resemble the cells of choanoflagellates. At present, the idea that ctenophores are basal metazoans remains an intriguing but controversial hypothesis.

bilaterian

Member of a clade of animals with bilateral symmetry and three germ layers. an enormous clade whose members (unlike sponges and cnidarians) have a two-sided or bilaterally symmetric form and a complete digestive tract, an efficient digestive system that has a mouth at one end and an anus at the other.

All bilaterally symmetrical animals have a third germ layer, called the

Mesoderm

reproduction in animals

Most animals reproduce sexually, and the diploid stage usually dominates the life cycle. In the haploid stage, sperm and egg cells are produced directly by meiotic division, unlike what occurs in plants and fungi

Hox genes

Most animals share a unique homeobox-containing family of genes, known as Hox genes. Hox genes play important roles in the development of animal embryos, controlling the expression of dozens or even hundreds of other genes that influence animal morphology

Ecdysozoa

One of the three main lineages of bilaterian animals; many ecdysozoans are moulting animals. These animals secrete external skeletons (exoskeletons) As the animal grows, it molts, squirming out of its old exoskeleton and secreting a larger one The process of shedding the old exoskeleton is called ecdysis.

The fossil record from the Ediacaran period (635-542 million years ago) also provides early evidence of predation.

Some animals of the time have a body protected by a shell that show signs of attack: round "bore holes" that resemble those formed today by predators that drill through the shells of their prey to gain access to the soft-bodied organisms lying within. Other small Ediacaran animals had shells or other defensive structures that may have been selected for because of predation. Overall, the fossil evidence indicates that the Ediacaran was a time of increasing animal diversity

Hallucigenia

Some fossils, like Hallucigenia, are perplexing, and it is difficult to distinguish what may be spines from legs or which end is the head. New electron microscopy approaches, however, are starting to reveal these details and are providing clues to the taxonomic position of these bizarre organisms. In the case of Hallucigenia, this work was able to distinguish spines, claws and a head with a simple pair of eyes and even teeth! These features provided evidence that Hallucigenia is distantly related to extant velvet worms (Ecdysoza)

Lophotrochozoa

Some lophotrochozoans, such as ectoprocts, develop a unique structure called a lophophore, a crown of ciliated tentacles that function in feeding Individuals in other phyla, including molluscs and annelids, go through a distinctive developmental stage called the trochophore larva

Which animals lack hox genes?

Sponges which are among the simplest extant animals, lack Hox genes However, they have other homeobox genes that influence their shape, such as those that regulate the formation of water channels in the body wall, a key feature of sponge morphology

Radial symmetry

Symmetry about a central axis.

Radial Symmetry

Symmetry in which the body is shaped like a pie or barrel (lacking a left side and a right side) and can be divided into mirror-imaged halves by any plane through its central axis. Sea anemones, for example, have a top side (where the mouth is located) and a bottom side. But they have no front and back ends and no left and right sides.

Most triploblastic animals have a body cavity T OR F

T

Why are muscle and nerve cells imp to animals?

The cells of most animals are organized into tissues, groups of similar cells that act as a functional unit. For example, muscle tissue and nervous tissue are responsible for moving the body and conducting nerve impulses, respectively. The ability to move and conduct nerve impulses underlies many of the adaptations that differentiate animals from plants and fungi.

archenteron

The endoderm-lined cavity, formed during gastrulation, that develops into the digestive tract of an animal.

Mesoderm

The middle primary germ layer in a triploblastic animal embryo; develops into the notochord, the lining of the coelom, muscles, skeleton, gonads, kidneys, and most of the circulatory system in species that have these structures.

Cleavage

The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote to a ball of cells.

How does radial symmetry help in the environment?

The symmetry of an animal generally fits its lifestyle. Many radial animals are sessile (living attached to a substrate) or planktonic (drifting or weakly swimming, such as jellies, commonly called jellyfish). Their symmetry equips them to meet the environment equally well from all sides.

ARE SPONGES MONOPHYLETIC?

Traditionally, sponges were placed in a single phylum, Porifera. This view began to change in the 1990s, when molecular studies indicated that sponges were paraphyletic; as a result, sponges were placed into several different phyla that branched near the base of the animal tree. Since 2009, however, several morphological and molecular studies have concluded that sponges are a monophyletic group after all

What was this common ancestor like, and how did animals arise from their single-celled ancestors?

a combination of morphological and molecular evidence indicates that choanoflagellates are among the closest living relatives of animals. Based on such evidence, researchers hypothesize that the common ancestor of living animals may have been a suspension feeder similar to present-day choanoflagellates

body plan

a particular set of morphological and developmental traits integrated into a functional whole—the living animal.

What kind of structural support do animal cells have?

a variety of proteins external to the cell membrane provide structural support to animal cells and connect them to one another - i.e. collagen The most abundant of these proteins is collagen, which is not found in plants or fungi.

How does bilateral symmetry help animals in their habitat?

bilateral animals typically move actively from place to place. Most bilateral animals have a central nervous system that enables them to coordinate the complex movements involved in crawling, burrowing, flying, or swimming.

fate of blastopore in protostomes

blastopore becomes mouth

fate of blastospore in deuterostomes

blastospore becomes anus the mouth is derived from the secondary opening

Pseudocoelom

body cavity that is formed from mesoderm and endoderm the animals that have one are called pseudocoelomates a pseudocoelom is not false; it is a fully functional body cavity

Why is dating the origin of animals hard?

dating the origin of animals is difficult, especially since the early animals lacked the hard, durable structures that normally fossilize well. Some researchers have used the presence of biomarkers in sediments to suggest the presence of specific animal groups. For example, in 710-million-year-old sediments, researchers have detected the chemical remains of certain steroids that today are primarily produced by a particular group of sponges. Hence, these fossil steroids suggest that animals had arisen by at least 710 million years ago.

Cnidarians and a few other animal groups that have only these two germ layers are said to be

diploblastic

Such animals have a

dorsal (top) side and a ventral (bottom) side, a left side and a right side, and an anterior (front) end and a posterior (back) end. Many animals with a bilaterally symmetrical body plan (such as arthropods and mammals) have sensory equipment concentrated at their anterior end, including a central nervous system ("brain") in the head—an evolutionary trend called cephalization

Triploblastic

has three germ layers: the ectoderm, endoderm, and mesoderm. (Although some diploblasts actually do have a third germ layer, it is not nearly as well developed as the mesoderm of animals considered to be triploblastic.)

Nutritional Mode of Animals

heterotrophs that ingest their food Unlike plants, animals cannot construct all of their own organic molecules and so, in most cases, they ingest them—either by eating other living organisms or by eating nonliving organic material. But unlike fungi, most animals do not feed by absorption; instead, animals ingest their food and then use enzymes to digest it within their bodies.

many animals have one of two developmental modes:

protostome development or deuterostome development

In deuterostome development, cleavage is

radial and indeterminate radial cleavage: The cleavage planes are either parallel or perpendicular to the vertical axis of the embryo; as seen at the eight-cell stage, the tiers of cells are aligned, one directly above the other - indeterminate cleavage, meaning that each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo. For example, if the cells of a sea urchin embryo are separated at the four-cell stage, each can form a complete larva. Similarly, it is the indeterminate cleavage of the human zygote that makes identical twins possible.

What groups lack true tissue?

sponges

In the ancestors of more complex animals, the Hox gene family arose how?

the Hox gene family arose via the duplication of earlier homeobox genes. Over time, the Hox gene family underwent a series of duplications, yielding a versatile "toolkit" for regulating development. In vertebrates, insects, and most other animals, Hox genes regulate the formation of the anterior-posterior (front-to-back) axis, as well as other aspects of development. Similar sets of conserved genes govern the development of both flies and humans, despite their obvious differences and hundreds of millions of years of divergent evolution.

The Cambrian period was followed by...

the Ordovician, Silurian, and Devonian periods, when animal diversity continued to increase, although punctuated by episodes of mass extinction

Vertebrates made the transition to land around 365 million years ago and diversified into numerous terrestrial groups. Two of these survive today:

the amphibians (such as frogs and salamanders) and the amniotes (reptiles, including birds, and mammals).

Bilaterians also diversified in two major clades that are composed entirely of invertebrates:

the ecdysozoans and the lophotrochozoans.

Animals with bilateral symmetry are __________blastic

triplo