BSC 2011 Chapters 32–34: Animal Diversity, Invertebrates & Vertebrates

What kingdom do all animals belong to?

Animalia

What is a defining characteristic of all animals?

Multicellularity

How do animals obtain their food?

Through ingestion; they cannot produce their own food.

What distinguishes animal cells from plant and fungal cells?

Animal cells lack rigid cell walls and are bounded only by a flexible plasma membrane.

What systems do most animals possess that allow for coordinated responses?

A nervous system and muscle tissue.

What is the term for the stage all animals pass through during embryonic development?

Blastula stage.

What major event in animal evolution occurred approximately 541-485 million years ago?

The Cambrian Explosion.

What are Hox genes responsible for in animal development?

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

What is a key factor that contributed to the Cambrian Explosion?

Increased oxygen levels in the atmosphere.

What type of animals develop only two germ layers?

Diploblastic animals.

What are the three germ layers in triploblastic animals?

Ectoderm, endoderm, and mesoderm.

What is the main difference between acoelomate and coelomate animals?

Acoelomates have no body cavity, while coelomates have a true coelom.

What is a pseudocoelomate?

An animal with a false body cavity that is only partially lined by mesoderm.

What is the significance of the mesoderm in triploblastic animals?

It allows for the development of true tissues and organs.

Which group of animals lacks true tissues, organs, nerves, and muscles?

Sponges (Porifera).

What is the function of the mesoglea in diploblastic animals?

It is a gelatinous layer between the ectoderm and endoderm, but not a true germ layer.

What type of symmetry do diploblastic animals typically exhibit?

Radial symmetry.

What type of symmetry do triploblastic animals typically exhibit?

Bilateral symmetry.

What is a key characteristic of all Bilateria?

They are triploblastic.

What evolutionary pressure drives the predator-prey arms race?

The development of novel attack structures by predators and new defenses by prey.

What is the role of the ectoderm in animal development?

It forms the outer body covering and nervous tissue.

What does the endoderm develop into in triploblastic animals?

The lining of the digestive tract and internal organs.

What are the consequences of being an acoelomate?

Limited size, no hydrostatic skeleton, and gas exchange by diffusion only.

What is a defining feature of coelomate animals?

They possess a true body cavity (coelom) that is fully lined with mesoderm.

What is the significance of the Cambrian Explosion in terms of animal diversity?

It marked a rapid increase in the diversity of animal phyla.

What is one major exam trap regarding animal classification?

Confusing fungi with animals; fungi are heterotrophic by absorption, not ingestion.

What is a coelomate?

An organism with a true body cavity completely lined by mesoderm (peritoneum).

List the four major advantages of having a coelom.

1) Hydrostatic skeleton 2) Cushioning of internal organs 3) Room for organ growth and complexity 4) Circulatory function.

What are examples of coelomates?

Annelids, Molluscs, Arthropods, Echinoderms, Chordates.

What is an acoelomate?

An organism with no body cavity, such as Platyhelminthes.

What defines the gametic life cycle in animals?

Animals alternate between haploid (gametes) and diploid (all other stages) stages through sexual reproduction.

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

The gametes themselves.

What is the diploid stage of the adult organism in humans?

2n = 46 chromosomes.

What occurs during meiosis in males and females?

Males produce sperm and females produce eggs, both haploid (n = 23).

What happens during fertilization?

A sperm and egg fuse to restore the diploid chromosome number (2n).

What is a blastula?

A hollow ball of cells produced by cleavage of the zygote, marking a hallmark stage of animal development.

What is gastrulation?

The process where blastula cells reorganize to form germ layers: ectoderm, mesoderm, and endoderm.

What is the fate of the blastopore in protostomes?

It becomes the mouth.

What is the fate of the blastopore in deuterostomes?

It becomes the anus.

Describe the cleavage pattern in protostomes.

Spiral and determinate cleavage.

Describe the cleavage pattern in deuterostomes.

Radial and indeterminate cleavage.

How does coelom formation differ between protostomes and deuterostomes?

Protostomes form coelom by schizocoely (splitting of mesoderm), while deuterostomes form it by enterocoely (outpocketing of gut).

What is a trochophore larva?

A free-swimming, ciliated larval form found in some protostomes like annelids and molluscs.

What defines Metazoa?

The clade containing all animals, characterized by multicellularity and heterotrophy by ingestion.

What is Eumetazoa?

All animals with true tissues, excluding Porifera (sponges).

What is the significance of Hox genes?

They are regulatory genes that control body axis development and contributed to the Cambrian Explosion.

What is bilateral symmetry?

A body plan where only one plane divides the body into mirror-image left and right halves.

What is radial symmetry?

A body plan where any plane through the central axis produces two mirror-image halves.

What is schizocoely?

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

What is enterocoely?

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

What are the three germ layers in triploblastic organisms?

Ectoderm, mesoderm, and endoderm.

What does the mesoderm form?

Muscles and most internal organs, but not the gut lining.

What does the endoderm form?

The lining of the digestive tract and other internal organs.

What is determinate cleavage?

Early cell fates are fixed (mosaic development); characteristic of protostomes.

What is indeterminate cleavage?

Early cells are totipotent; characteristic of deuterostomes, allowing for identical twins.

What are the two sub-clades of protostomes?

Lophotrochozoa and Ecdysozoa.

What characterizes Lophotrochozoa?

Presence of a lophophore and/or trochophore larva; includes Platyhelminthes, Mollusca, Annelida.

What characterizes Ecdysozoa?

Animals that molt their external cuticle or exoskeleton; includes Nematoda, Arthropoda, Tardigrada.

What is the significance of echinoderms in relation to deuterostomes?

Echinoderms are deuterostomes despite adult radial symmetry; their larvae are bilaterally symmetrical.

What defines a tissue in animals?

A collection of specialized cells of the same type, isolated by membranes; sponges lack tissues.

What does 'dorsal' refer to in bilaterally symmetrical animals?

The 'top' (back) side.

What does 'ventral' refer to in bilaterally symmetrical animals?

The 'bottom' (belly) side.

What does 'anterior' refer to in bilaterally symmetrical animals?

The head/front end.

What does 'posterior' refer to in bilaterally symmetrical animals?

The tail/rear end.

What is diploblastic?

Having only two embryonic germ layers: ectoderm and endoderm; characteristic of radially symmetrical animals.

What is triploblastic?

Having three embryonic germ layers: ectoderm, mesoderm, and endoderm; characteristic of bilaterally symmetrical animals.

What is the function of the endoderm?

Gives rise to the lining of the digestive tract, liver, and lungs.

What is the function of the ectoderm?

Gives rise to the outer body covering (skin) and the central nervous system (CNS).

What is the function of the mesoderm?

Gives rise to muscles and most internal organs in triploblastic animals.

What is a coelom?

A true body cavity found in coelomates, derived entirely from mesoderm.

What is a pseudocoelom?

A false body cavity that forms between the mesoderm and endoderm, not fully lined by mesodermal tissue.

What is spiral cleavage?

Cleavage pattern in protostomes where cells divide at an oblique angle, causing daughter cells to sit offset.

What is radial cleavage?

Cleavage pattern in deuterostomes where cells divide parallel or perpendicular to the main axis.

What is a blastopore?

The opening of the archenteron that forms during gastrulation; becomes mouth in protostomes and anus in deuterostomes.

What is the phylogenetic position of Porifera?

Basal Metazoa; sister group to all other animals; lack true tissues.

What is the common feeding mode of sponges?

Filter feeding via choanocytes.

What are choanocytes?

The defining cells of sponges that create water currents for filter feeding.

What is the spongocoel?

The central cavity of a simple sponge.

What is a spongocoel?

The central cavity of a simple sponge where water flows through.

What is the path of water flow in a sponge?

Pores (ostia) → spongocoel → osculum.

What is mesohyl?

A gelatinous protein-rich matrix in sponges that contains amoebocytes.

What are gemmules?

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

How do sponges reproduce?

They reproduce sexually and asexually; gemmules allow for survival and regeneration.

What are the defining characteristics of sponges?

Multicellular, eukaryotic, heterotrophic by ingestion, lack cell walls, and reproduce sexually.

Why are sponges not considered Eumetazoa?

They lack true tissues.

What is the primary feeding method of sponges?

Digestion is only intracellular.

What is the common name for Phylum Cnidaria?

Jellyfish, corals, sea anemones, and hydra.

What type of symmetry do Cnidarians exhibit?

Radial symmetry (some bilateral in larva or Cubozoa).

What are cnidocytes?

Specialized stinging cells in Cnidarians that contain nematocysts.

What is a nematocyst?

A coiled, venomous thread in a capsule that can inject venom or entangle prey.

What are the two body forms of Cnidarians?

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

What is the gastrovascular cavity (GVC) in Cnidarians?

A central digestive cavity with only one opening (mouth = anus).

What is mesoglea?

A gelatinous, non-cellular matrix in Cnidarians that provides buoyancy.

What is the reproductive strategy of most Cnidarians?

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

What is coral bleaching?

The expulsion of zooxanthellae from corals due to stress, leading to visible CaCO3 skeletons.

What are the four classes of Cnidaria?

Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa.

What is a key feature of Class Hydrozoa?

Alternation of polyp and medusa forms; some are colonial.

What distinguishes Class Scyphozoa?

Large medusa form is dominant; polyp stage is small/reduced.

What is unique about Class Cubozoa?

They have a cube-shaped medusa and are among the most venomous Cnidarians.

What is the defining characteristic of Class Anthozoa?

They have only a polyp stage and no medusa stage.