Mastering Biology Chapter 32

germ layers

Three main layers that form the various tissues and organs of an animal body. ectoderm, endoderm, and mesoderm

Cenozoic Era

(66 Million Years Ago to the Present) Mass extinctions of both terrestrial and marine animals ushered in a new era, the Cenozoic. Among the groups of species that disappeared were the large, nonflying dinosaurs and the marine reptiles. The fossil record of the early Cenozoic documents the rise of large mammalian herbivores and predators as mammals began to exploit the vacated ecological niches. The global climate gradually cooled throughout the Cenozoic, 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.

Neoproterozoic Era

1 billion- 542 million years ago, Era in which the first animals were found (Edicaran Fauna) 1b-542 mya; first macroscopic fossils (565-560 mya), named the ediacaran biota for the site of initial discovery

hemocoel

A body cavity lined by tissue derived from mesoderm and by tissue derived from endoderm. a body cavity that forms between the mesoderm and endoderm​ (Figure 32.9b). A h​emocoel contains ​hemolymph, a fluid that​ functions in the internal transport of nutrients and waste. Hemolymph is analogous to your blood and is circulated through the body cavity in an open system by the heart.

metamorphosis

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

body cavity

A fluid- or air-filled space between the digestive tract (endoderm) and the body wall (ectoderm). Body cavities have diverse functions, such as to provide structural support and to facilitate the internal transport of nutrients, gases, and wastes.

Blastula

A hollow ball of cells that marks the end of the cleavage stage during early embryonic development in animals.

homeoboxes

A homeobox is a DNA sequence found within genes that are involved in the regulation of patterns of anatomical development morphogenesis in animals, fungi, and plants. A homeobox is about 180 base pairs long. It encodes a protein domain (the homeodomain) which when expressed (i.e. as protein) can bind DNA.

Bilaterans

A member of a clade of animals with bilateral symmetry and three germ layers. bilaterians include molluscs, arthropods, chordates, and most other living animal phyla.

Eumetazoans

A member of a clade of animals with true tissues. All animals except sponges and a few other groups are eumetazoans. Members of this group have tissues, such as muscle tissue and nervous tissue. Basal eumetazoans, which include the phyla Ctenophora (comb jellies) and Cnidaria, are diploblastic and generally have radial symmetry.

Are the Acoela basal bilaterians?

A series of recent papers—including a 2016 phylogenomic study—have indicated that flatworms in phylum Acoela are basal bilaterians, as shown in Figure 32.11. A different conclusion was supported by one recent analysis, which placed members of the Acoela within Deuterostomia. Researchers are sequencing the genomes of additional species in the phylum and in closely related groups to provide a more definitive test of the hypothesis that the Acoela are basal bilaterians. If further evidence supports this hypothesis, bilaterians may have descended from a common ancestor that resembled this group of living flatworms—that is, an ancestor that had a simple nervous system, a saclike gut with a single opening (the "mouth"), and no excretory system.

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. Most animals with deuterostome development also have 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.

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.

invertabrates

An animal without a backbone; invertabrates make up 95% of animal species

ediacaran biota

An early group of macroscopic, mostly softbodied, multicellular eukaryotes known from fossils that range in age from 635 million to 541 million years old. Although data from fossil steroids and molecular clocks indicate an earlier origin, the first generally accepted macroscopic fossils of animals date from about 560 million years ago. These fossils are members of an early group of mostly soft-bodied multicellular eukaryotes, known collectively as the Ediacaran biota. The name comes from the Ediacara Hills of Australia, where fossils of these organisms were first discovered​.

gastrula

An embryonic stage in animal development encompassing the formation of three layers: ectoderm, mesoderm, and endoderm.

tissues

An integrated group of cells with a common structure, function, or both.

cell structure and specialization of animals

Animals are eukaryotes, and like plants and most fungi, animals are multicellular. In contrast to plants and fungi, however, animals lack the structural support of cell walls. Instead, proteins external to the cell membrane provide structural support to animal cells and connect them to one anot​her. The most ab​undant of these proteins is collagen, which is not found in plants or fungi.

pseudocoelomates

Animals with only a hemocoel once were called pseudocoelomates (from the Greek pseudo, false) and the cavity, a pseudocoelom. Hemocoels and coeloms have been independently gained or lost multiple times in the course of animal evolution; hence, their presence or absence is not a good indicator of phylogenetic relationships.

Cambrian explosion

Another wave of animal diversification occurred 535-525 million years ago, early in the Cambrian period of the Paleozoic era—a phenomenon referred to as the Cambrian explosion (see ​Concept 25.3). In strata​ formed before the Cambrian explosion, only a few animal phyla have been observed. But in strata that are 535-525 million years old, paleontologists have found the oldest fossils of about half of all extant animal phyla, including the first arthropods, chordates, and echinoderms.

diploblastic

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

trochophore larva

Distinctive larval stage observed in some lophotrochozoan animals, including some annelids and molluscs.

acoelomates

Finally, some triploblastic animals lack a body cavity altogether (Figure 32.9c). These compact animals tend to have thin, flat bodies. Such animals don't require an internal transport system: With bodies that are only a few cells thick, the exchange of nutrients, gases, and wastes can occur across the entire body surface. These animals are sometimes called acoelomates (from the Greek a-, without).

what two things set animals apart from plants and fungi?

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 (which lack muscle and nerve cells). For this reason, muscle and nerve cells are central to the animal lifestyle.

In particular, most animals share a unique homeobox-containing family of genes, known as... which do what?

Hox genes. Hox genes play important roles in the development of animal embryos, controlling the expression of many other genes that influence morphology.

blastopore

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

gastrulation

In animal development, a series of cell and tissue movements in which the blastula-stage embryo folds inward, producing a three-layered embryo, the gastrula.

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.

protosome development

In animals, a developmental mode distinguished by the development of the mouth from the blastopore; often also characterized by spiral cleavage and by the body cavity forming when solid masses of mesoderm split. Many animals with protostome development undergo spiral cleavage, in which the planes of cell division are diagonal to the vertical axis of the embryo; as seen in the eight-cell stage of the embryo, smaller cells are centered over the grooves between larger, underlying c​ells

bilateral symmetry

In contrast, bilateral animals typically move actively from place to place. Nearly all animals with a bilaterally symmetric body plan (such as arthropods and mammals) have sensory equipment concentrated at the head end of their body, including a central nervous system ("brain"). This central nervous system enables them to coordinate the complex movements involved in crawling, burrowing, flying, or swimming.

body plan

In multicellular eukaryotes, a set of morphological and developmental traits that are integrated into a functional whole—the living organism.

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 (see Figure 32.11). This conclusion was supported in a 2017 phylogenomic analysis, but several other studies have placed the comb jellies (phylum Ctenophora) at the base of the animal tree. In addition to the most recent phylogenomic results, data 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 (see Figure 32.3), and the fact that sponges are one of the few animal groups that lack tissues (as might be expected for basal animals). Ctenophores, on the other hand, have 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.

reproduction and development of animals

Most animals reproduce sexually, and the diploid stage usually dominates the life cycle. In most animal species, a small, flagellated sperm fertilizes a larger, nonmotile egg, forming a diploid zygote. The zygote then undergoes cleavage, a succession of mitotic cell divisions without cell growth between the divisions. During the development of most animals, cleavage leads to the formation of a multicellular embryonic stage called a blastula, which in many animals takes the form of a hollow ball. Following this 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.

Deuterostomia

One of the three main lineages of bilaterian animals. See also Ecdysozoa and Lophotrochozoa. thus, the​ term deuterostome ​refe​rs​ not only to a mode of animal development, but also to the members of this clade. (The dual meaning of this term can be confusing since some organisms with a deuterostome developmental pattern ​are not members of clade Deu​terostomia.)

Lophotrochozoa

One of the three main lineages of bilaterian animals; lophotrochozoans include organisms that have lophophores or trochophore larvae. See also Deuterostomia and Ecdysozoa. refers to two different features observed in some animals belonging to this clade ​(Figure 32.12). So​me lophotrochozoans, such as ectoprocts, develop a unique structure called a lophophore (from the Gre​ek lophos, crest, and pherein, to ​​​​​carry​), a crown ​of ciliated tentacles that function in feeding​ (see Figure 32.12a). Individuals in other phy​la, including molluscs and annelids, go through a distinctive developmental stage called the trochophore larva (see Figure 32.12b)—h​ence the name lophotrochozoan​.

Ecdysozoa

One of the three main lineages of bilaterian animals; many ecdysozoans are molting animals. See also Deuterostomia and Lophotrochozoa. refers to a characteristic shared by nematodes, arthropods, and some of the other ecdysozoan phyla that are not included in our survey. These animals secrete external skeletons (exoskeletons); the stiff covering of a cricket and the flexible cuticl​e of a nematode are examples. As the animal grows, it molts, squirming out of its old exoskeleton and secreting a larger one.

Triploblastic

Possessing three germ layers: the endoderm, mesoderm, and ectoderm. All bilaterian animals are triploblastic. Thus, animals with bilateral symmetry are also said to be triploblastic (having three germ layers). In triploblasts, the mesoderm forms the muscles and most other organs between the digestive tract and the outer covering of the animal. Triploblasts include a broad range of animals, from flatworms to arthropods to vertebrates. (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.)

Fate of the Blastopore

Protostome and deuterostome development often differ in the fate of the blastopore, the indentation that during gastrulation leads to the formation of the arc​henteron (Figure 32.10c). Aft​er 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. In protostome development, the mouth generally develops from the first opening, the blastopore, and it is for this characteristic that the term protostome derives (from the Greek protos, first, and stoma, mouth). In deuterostome development (from the Greek deuteros, second), the mouth is derived from the secondary opening, and the blastopore usually forms the anus.

archenteron

The endodermlinedcavity, formed during gastrulation, that develops into the digestive tract of an animal. During gastrulation, an embryo's developing digestive tube initially forms as a blind pouch, the archenteron, which b​​ecomes the gut. As the archenteron forms​ in protosto​me development, initially solid masses of mesoderm split and form the coelom. In contrast, in deuterostome development, the mesoderm buds from the wall of the archenteron, and its cavity becomes the coelom.

endoderm

The innermost of the three primary germ layers in animal embryos; lines the archenteron and gives rise to the liver, pancreas, lungs, and the lining of the digestive tract in species that have these structures. 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 to the lining of organs such as the liver and lungs of vertebrates.

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. All bilaterally symmetrical animals have a third germ layer, called the mesoderm, which fills much of the space between the ectoderm and endoderm. Thus, animals with bilateral symmetry are also said to be triploblastic (having three germ layers). In triploblasts, the mesoderm forms the muscles and most other organs between the digestive tract and the outer covering of the animal. Triploblasts include a broad range of animals, from flatworms to arthropods to vertebrates. (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.)

ectoderm

The outermost of the three primary germ layers in animal embryos; gives rise to the outer covering and, in some phyla, the nervous system, inner ear, and lens of the eye. 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.

ecdysis

The process of shedding the old exoskeleton is called ecdysis.

nutritional mode of animals

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 feed by ingesting their food and then using enzymes to digest it within their bodies. heterotrophs that ingest their food

In a phylogenetic tree, a lineage that diverges from all other members of its group early in the evolutionary history of the group is described as

a basal taxon. In a phylogenetic tree that is rooted, a branch point within the tree (often drawn farthest to the left) represents the most recent common ancestor of all taxa in the tree. A lineage that diverges from all other members of its group early in the history of a group is called a basal taxon. Hence, a basal taxon lies on one of the two branches that diverge near the common ancestor of the group. Note that the lineages represented by these two branches originated at the same point in time and hence they have been evolving for the same length of time.

larva

a sexually immature form of an animal that is morphologically distinct from the adult, usually eats different food, and may even have a different habitat than the adult, as in the case of the aquatic larva of a mosquito or dragonfly A free-living, sexually immature form in some animal life cycles that may differ from the adult animal in morphology, nutrition, and habitat.

coelom

body cavity lined/derived only from the mesoderm Many triploblastic animals have a coelom (from the Greek koilos, hollow), a body cavity that forms from tissue derived from mesoderm. The inner and outer layers of mesoderm that surround the cavity connect and form structures that suspend the internal organs A coelom's fluid cushions the suspended organs, helping to prevent internal injury. In soft-bodied animals, such as earthworms, the fluid in the coelom acts like a skeleton against which muscles can work. A coelom also 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. Animals possessing coeloms are sometimes called coelomates.

radial symmetry

body plan in which body parts repeat around the center of the body Many radial animals are sessile (living attached to a substrate) or planktonic (drifting or weakly swimming, such as jellies, commonly called jellyfishes). Their symmetry equips them to meet the environment equally well from all sides.

Which of the following is the most inclusive term for an organism that obtains organic food material by eating other organisms or substances derived from them?

heterotroph

cadherin proteins

link epithelial cells together by binding to similar cadherins in adjacent epithelial cells. bind cells in multicellular animals

Mesozoic Era

middle life (252-66 Million Years Ago); rise of mammals and dinosaurs; the rise of birds; extinction of dinosaurs, rise of flowering plants middle era of the phanerozoic eon, age of reptiles In the oceans, the first coral reefs formed, providing other marine animals with new places to live. Some reptiles returned to the water, leaving ​plesiosaurs (see Figure 34.25) and other large aquatic​ predators as their descendants. On land, descent with modification in some tetrapods led to the origin of wings and other flight equipment in pterosaurs and birds. Large and small dinosaurs emerged, as both predators and herbivores. At the same time, the first mammals—tiny nocturnal insect-eaters—appeared on the scene. In addition, as you re​ad in Concept 30.3, flowering plants (​angiosperms) and insects both underwent dramatic diversifications during the late Mesozoic.

what is the protist group most closely related to animals?

morphological and molecular evidence point to choanoflagellates as the closest living relatives of animals. Based on such evidence, researchers have hypothesized that the common ancestor of choanoflagellates and living animals may have been a suspension feeder similar to present-day choanoflagellates.

symmetry

radial and bilateral A basic feature of animal bodies is their type of symmetry—radial or bilateral—or absence of symmetry. Fossil evidence indicates that these two fundamentally different kinds of symmetry have existed for at least 550 million years.

A mutualism is an ecological relationship between two species...

that both benefit from the relationship.

the study of evo-devo

the interface between evolution and development

Paleozoic Era

the part of geologic time (541-252 Million Years Ago) ; invertebrates, fishes, amphibians, reptiles, ferns, and cone-bearing trees were dominant the oldest era - immediately after Precambrian; organisms developed hard parts

Zoologists currently recognize about how many phyla of extant animals?

three dozen phyla of extant animals