BSC 2011 Chapters 32–33: Animal Diversity and Invertebrate Phyla

What kingdom do all animals belong to?

Animalia

What is a defining feature of animals regarding cell structure?

Animals are multicellular and composed of eukaryotic cells.

How do animals obtain their food?

Animals are heterotrophic by ingestion, meaning they consume and digest organic matter.

Do animal cells have cell walls?

No, animal cells lack rigid cell walls and are bounded by a flexible plasma membrane.

What systems do most animals possess for responding to their environment?

Most animals have a nervous system and muscle tissue.

What is a key characteristic of animal motility?

Animals are capable of movement at some point in their life cycle.

What type of reproduction is most common in animals?

Most animals reproduce sexually, producing haploid gametes that fuse to form a diploid zygote.

What developmental stage is unique to animals?

All animals pass through a blastula stage during embryonic development.

What significant event in animal evolution occurred around 541-485 million years ago?

The Cambrian Explosion, marked by a rapid increase in animal diversity.

What are the three main reasons for the Cambrian Explosion?

Increased oxygen and ozone levels, evolution of the Hox gene complex, and predator-prey arms race.

What is the role of Hox genes in animal development?

Hox genes control the development of body form along the anterior-posterior axis.

What distinguishes diploblastic animals from triploblastic animals?

Diploblastic animals have two germ layers (ectoderm and endoderm), while triploblastic animals have three (ectoderm, mesoderm, and endoderm).

What is an example of a diploblastic animal?

Cnidaria, which includes jellyfish and corals.

What is the significance of body cavities in triploblastic animals?

Body cavities (coeloms) are fluid-filled spaces that play a crucial role in organ development and function.

What are the three types of body cavities?

Acoelomate (no body cavity), pseudocoelomate (false body cavity), and coelomate (true body cavity).

What is acoelomate?

Acoelomates have no fluid-filled body cavity and are completely filled with solid mesoderm-derived tissue.

What defines a pseudocoelomate?

Pseudocoelomates have a fluid-filled pseudocoelom partially lined by mesoderm.

What is a coelomate?

Coelomates have a true coelom completely lined by mesoderm.

What is the role of mesoderm in triploblastic animals?

Mesoderm develops into muscles and most internal organs.

What is the consequence of being an acoelomate?

Acoelomates have limited size and rely on diffusion for gas exchange.

What is the significance of the blastula stage?

The blastula stage is crucial for the formation of germ layers and body structures during development.

What is the main difference between true tissues and true organs?

True tissues are specialized groups of cells, while true organs are structures composed of multiple tissue types.

What is the main distinction between radial and bilateral symmetry?

Radial symmetry allows for multiple planes of division, while bilateral symmetry has a single plane of division.

What is the significance of the Cambrian Explosion in evolutionary history?

It marks the appearance of virtually all major animal phyla in the fossil record.

What does the term 'motility' refer to in animals?

Motility refers to the ability of animals to move at some stage in their life cycle.

How do diploblastic animals develop true tissues without true organs?

They have two germ layers but lack a mesoderm, which is necessary for organ development.

List the four major advantages of having a true coelom.

1) Hydrostatic skeleton, 2) cushioning of internal organs, 3) room for organ growth and complexity, 4) circulatory function.

What is the defining feature of an acoelomate?

It has no body cavity.

What type of body cavity do pseudocoelomates have?

A pseudocoelom, which is partially lined by mesoderm.

Describe the gametic life cycle of animals.

Animals alternate between haploid (gametes) and diploid (zygote, embryo, etc.) stages.

What is the only haploid stage in the gametic life cycle?

The gametes themselves.

What happens during fertilization in the gametic life cycle?

A sperm and egg fuse to form a diploid zygote.

What is the blastula?

A hollow ball of cells formed during the cleavage of the zygote.

What occurs during gastrulation?

Cells of the blastula rearrange to form germ layers: ectoderm, mesoderm, and endoderm.

What is the fate of the blastopore in protostomes?

It becomes the mouth.

What type of cleavage occurs in protostomes?

Spiral, determinate cleavage.

How does coelom formation differ between protostomes and deuterostomes?

Protostomes use schizocoely (splitting of mesoderm), while deuterostomes use enterocoely (outpocketing of the gut).

What larval form is associated with the Lophotrochozoa clade?

Trochophore larva.

What is the defining characteristic of the Eumetazoa clade?

All animals with true tissues.

What does the term 'bilateria' refer to?

Animals with bilateral symmetry, including both protostomes and deuterostomes.

What are Hox genes?

Regulatory genes that control the development of the anterior-posterior body axis in animals.

What is the Cambrian Explosion?

A rapid diversification of animal body plans that occurred around 541 million years ago.

What is the significance of the mesoderm in triploblastic organisms?

It enables the formation of muscles and most internal organs.

Which germ layer forms the epidermis and nervous system?

Ectoderm.

What is the role of the endoderm?

It forms the lining of the digestive tract and other internal organs.

What is a pseudocoelom?

A body cavity that is not completely lined by mesoderm, found in nematodes.

What is the difference between diploblastic and triploblastic organisms?

Diploblastic organisms have two germ layers (ectoderm and endoderm), while triploblastic organisms have three (ectoderm, mesoderm, and endoderm).

What are the two major superphyla of animals based on embryonic development?

Protostomia and Deuterostomia.

What is the primary characteristic of deuterostomes?

The blastopore becomes the anus, and the mouth forms secondarily.

What is the significance of genetic recombination during meiosis?

It increases genetic diversity in gametes.

What is the role of the morula in animal development?

It is a solid ball of cells that forms after cleavage of the zygote.

What type of cleavage is associated with deuterostomes?

Radial, indeterminate cleavage.

What is the function of the coelom?

It acts as a hydrostatic skeleton and provides space for organ development.

What are the three main causes of animal diversity?

Rising O₂/O₃ levels, Hox gene evolution, predator-prey arms race.

What is radial symmetry?

A body plan where any plane through the central axis produces two mirror-image halves, found in Cnidaria and adult Echinodermata.

What is bilateral symmetry?

A body plan where only one plane (the sagittal plane) divides the body into mirror-image left and right halves, associated with active movement.

What is schizocoely?

A method of coelom formation in protostomes where the coelom forms by splitting solid mesodermal blocks.

What is enterocoely?

A method of coelom formation in deuterostomes where the coelom forms from outpocketings of the archenteron.

What is determinate cleavage?

Early cell fates are fixed; characteristic of protostomes.

What is indeterminate cleavage?

Early cells are totipotent; characteristic of deuterostomes and the basis for identical twins.

What are the three evolutionary superphyla of invertebrates?

Lophotrochozoa, Ecdysozoa, and Deuterostomia.

What is the significance of Metazoa in animal phylogeny?

It represents all animals characterized by multicellularity, heterotrophy by ingestion, and the blastula stage.

What distinguishes Porifera from Eumetazoa?

Porifera lack true tissues and are considered parazoa.

What is the common name for the phylum Cnidaria?

Jellyfish, corals, sea anemones, hydra, and box jellies.

What type of symmetry do Cnidarians exhibit?

Radial symmetry.

What is the body cavity type in Cnidarians?

Gastrovascular cavity (GVC), which is an incomplete digestive system.

What are cnidocytes?

Specialized stinging cells in Cnidarians that contain nematocysts.

What are the two body forms of Cnidarians?

Polyp (sessile) and medusa (free-swimming).

What is the role of choanocytes in sponges?

They create water currents for filter feeding and trap food particles.

What is mesohyl in sponges?

A gelatinous matrix that contains amoebocytes for nutrient transport and gamete production.

What are gemmules?

Clusters of amoebocytes enclosed in a resistant coat, produced during unfavorable conditions for asexual reproduction.

What is the feeding strategy of Porifera?

Filter feeding via choanocytes.

What is the habitat of most sponges?

Mostly marine, with some freshwater species.

What is the significance of Echinodermata's radial symmetry?

Echinoderms evolved from bilaterally symmetrical ancestors; their adult radial symmetry is secondary.

Why is 'Invertebrates' considered a paraphyletic group?

'Invertebrates' excludes vertebrates, which share a common ancestor with echinoderms.

What type of skeleton do Cnidarians have?

Hydrostatic skeleton; some corals secrete CaCO3 exoskeletons.

What type of digestion occurs in Cnidarians?

Extracellular digestion in the gastrovascular cavity and intracellular digestion.

What is the reproductive strategy of Cnidarians?

Alternation of generations: polyp (asexual) and medusa (sexual).

What is the primary distinction of Porifera in terms of tissue organization?

They do not have true tissues or organs.

What is the function of the spongocoel in sponges?

It is the central cavity where water flows through and exits via the osculum.

What is the significance of the blastopore in protostomes?

In protostomes, the blastopore develops into the mouth.

What is the significance of the blastopore in deuterostomes?

In deuterostomes, the blastopore develops into the anus.

What are the four classes of Cnidaria?

Hydrozoa, Scyphozoa, Cubozoa, Anthozoa

What is the dominant form of Hydrozoa?

Polyp (colonial or solitary)

Name a key feature of Scyphozoa.

Large medusa; polyp stage small/reduced

What distinguishes Cubozoa from other cnidarians?

Cube-shaped medusa and sophisticated lens eyes

Which class of Cnidaria has no medusa stage?

Anthozoa

What is the life cycle of cnidarians characterized by?

Alternation of generations between polyp and medusa stages

What happens to corals during stress conditions?

They expel zooxanthellae, leading to coral bleaching

What is the defining characteristic of Platyhelminthes?

They are acoelomate flatworms

What type of symmetry do Platyhelminthes exhibit?

Bilateral symmetry

What is the primary feeding method of free-living Platyhelminthes?

Predation or scavenging using a pharynx

How do parasitic Platyhelminthes absorb nutrients?

Through the tegument, with no digestive system in Cestoda

What are the four classes of Platyhelminthes?

Turbellaria, Monogenea, Trematoda, Cestoda

What is a key feature of Turbellaria?

Ciliated ventral surface and regeneration ability

What distinguishes Cestoda from other Platyhelminthes?

They have no digestive system and absorb nutrients through the tegument

What is the role of flame cells in Platyhelminthes?

They filter and remove metabolic waste and excess water

What is the significance of the gastrovascular cavity (GVC) in flatworms?

It serves as a digestive cavity with a single opening

What is the primary habitat of Platyhelminthes?

Marine, freshwater, terrestrial, and parasitic in animals

What is the function of the radula in mollusks?

It is a rasping structure used for feeding