10. Animal Diversity (V)

Do animal cells have cell walls?

No. Animal cells have a cell membrane but no cell wall.

Are all animals unicellular or multicellular?

All animals are multicellular; there are no unicellular animals, though some are microscopic.

What is a tissue?

A group of cells that share the same structure and work together for a specific function (e.g., muscle tissue, epidermal tissue).

What does heterotrophic mean in animals?

They feed on organic molecules by ingesting them; they are heterotrophs and ingestive feeders.

What is the difference between motile and sessile in animals?

Motile means capable of moving; sessile means fixed in place; many animals are sessile as adults but were motile at some life stage.

What is the typical pattern of animal embryonic development?

Most animals share a similar embryonic development from zygote to early embryo, often with larval stages.

When did the common ancestor of animals live and what was it?

About 770 million years ago; it was multicellular.

What is the colonial hypothesis for the origin of multicellularity in animals?

A colony of connected choanoflagellate-like cells that over time specialized into feeding, sensing, and reproductive roles, forming a multicellular animal.

What is a choanoflagellate?

A single-celled eukaryote with a collar and a flagellum, considered the closest living relative of animals.

How could a choanoflagellate colony become a multicellular animal?

Cells divide by mitosis and stay together, then specialize in different functions to form a cohesive organism.

What two types of features would be needed for the colony-to-multicellular transition?

Extracellular adhesion molecules to stick cells together and cell signaling between cells.

What sponge features support the choanoflagellate–animal ancestor link?

Sponges have choanocyte-like cells and cadherin proteins similar to those in choanoflagellates and animals.

What is the role of cadherin proteins in animal evolution?

Cadherins are cell adhesion proteins; their presence in both choanoflagellates and animals suggests the mechanism for cell adhesion in the origin of multicellularity; a change in the cadherin gene marks the animal lineage.

To which major supergroup do animals and choanoflagellates belong?

Unikonta.

What is the difference between a colony and a multicellular organism in this context?

A colony consists of individual cells performing all functions; a multicellular organism has differentiated cells with specialized roles.

What is the process called when the zygote divides by mitosis to form the early embryo?

Cleavage (mitotic cell division).

What is the hollow ball of cells formed after cleavage and filled with fluid called?

Blastula.

What embryonic process involves inward migration of cells from the blastula to form a layered embryo?

Gastrulation.

What are the three embryonic tissue layers formed during gastrulation?

Ectoderm, endoderm, and mesoderm.

Which embryonic tissue develops into the skin and nervous system?

Ectoderm.

Which embryonic tissue develops into the digestive system?

Endoderm.

Which embryonic tissue gives rise to muscles and many organs including the skeleton and reproductive organs?

Mesoderm.

What is the opening in the gastrula called that develops into the mouth or anus depending on the animal?

Blastopore.

How many germ layers do cnidarians (e.g., jellyfish) have?

Two (diploblastic).

In a cross-section during early organ formation, which layer lies on the outside and forms the epidermis and nervous system?

Ectoderm.

What term is used for the embryonic tissues that differentiate into the embryo's tissues?

Embryonic tissues (the three germ layers: ectoderm, endoderm, and mesoderm).

Which germ layer forms around the intestine and the body wall, including muscles?

Mesoderm.

Which organism is used in the video to demonstrate embryonic development (the purple sea urchin)?

Purple sea urchin.

What is the fertilized egg called?

Zygote.

What is the ploidy of the zygote?

Diploid.

What group of genes regulate embryo development and determine the body plan in most animals (except sponges)?

Hox genes.

What does the term 'body plan' refer to in animals?

The overall form of the body, including shape, symmetry, arrangement of structures, and location of limbs.

What are the three main symmetry categories used to describe animals?

Asymmetric, radial, and bilateral symmetry.

Which animals are truly asymmetric?

Sponges (they lack symmetry).

What characterizes radial symmetry?

Body parts arranged around a central axis; multiple planes can yield equal halves (e.g., sea anemones, jellyfish).

What characterizes bilateral symmetry?

Body has two sides; only one plane yields equal halves; includes most animals like humans.

What is cephalization?

Development of a head with sensory organs and a brain; typical in bilateral animals.

In bilateral animals, what is concentrated in the head region?

Sensory organs and brain; contrast with radial animals where sensory cells are distributed around the body.

What are the four directional terms used for bilateral animals?

Dorsal (back), ventral (belly), anterior (head end), posterior (tail end).

What are the embryonic tissue layers in animals, and which group lacks them?

Ectoderm, endoderm, and (in triploblastic animals) mesoderm; sponges lack true tissue layers.

Which phylum is diploblastic?

Cnidaria.

What is a coelom?

A true body cavity between the digestive tract and the body wall, formed from mesoderm.

What is an acoelomate organism?

An animal with no body cavity; space between gut and body wall is filled with tissue (e.g., flatworms).

What is a pseudocoelomate organism?

An animal with a pseudocoelom—a body cavity between endoderm and mesoderm; lacks a true muscular layer around the intestine.

What is a coelomate organism?

An animal with a true coelom; the body cavity is lined by mesoderm; has mesenteries to hold organs.

What are mesenteries?

Tissue derived from mesoderm that anchors internal organs and blood vessels.

What are the functions of a body cavity?

To provide space for organs, offer protection, and enable a hydrostatic skeleton for movement.

What is a hydrostatic skeleton?

A fluid-filled cavity that provides support and aids movement.

What does protostome development mean for the mouth and blastopore?

The mouth forms first; the blastopore becomes the mouth; often shows spiral cleavage and determinate development.

What does deuterostome development mean for the mouth and blastopore?

The mouth forms second; the blastopore becomes the anus; typically shows radial cleavage and indeterminate development.

What is spiral cleavage and with which development type is it associated?

Off-center (spiral) arrangement of daughter cells; associated with protostomes; typically determinate fate.

What is radial cleavage and with which development type is it associated?

Daughter cells align directly above one another; associated with deuterostomes; typically indeterminate fate and can lead to identical twins.

Which type of cleavage allows for the possibility of identical twins?

Radial/indeterminate cleavage (as in many deuterostomes) can allow identical twins when the embryo splits.

How does coelom formation differ between protostomes and deuterostomes according to the notes?

In protostomes, the coelom forms as mesoderm develops; in deuterostomes, endodermal tissue can pinch off to form the coelom.

What is the phylum of sponges?

Porifera

Which phylum includes jellyfish and sea anemones?

Cnidaria

Which phylum includes starfish?

Echinodermata

To which phylum do fish and other vertebrates belong?

Chordata

Which phylum contains flatworms?

Platyhelminthes

Which phylum includes snails, slugs, mussels, and clams?

Mollusca

Which phylum includes earthworms?

Annelida

Which phylum includes nematodes?

Nematoda

Which phylum includes arthropods such as crabs and insects?

Arthropoda

What does Metazoa refer to?

All animals

What is Eumetazoa?

Animals with tissues

What does Bilateria refer to?

Bilateral animals

Name the three major clades of Bilateria.

Lophotrochozoa, Ecdysozoa, Deuterostomia

Which phyla are in Ecdysozoa?

Nematoda and Arthropoda

What is the defining feature of Ecdysozoa?

They molt (ecdysis) to grow

Which phyla are in Lophotrochozoa?

Platyhelminthes, Mollusca, Annelida

What two features give Lophotrochozoa its name?

Trochophore larva or a lophophore feeding structure

What is Deuterostomia?

A clade with deuterostome development; includes Echinodermata and Chordata

What does deuterostome development mean?

Mouth forms second, anus forms first

Which two phyla are classic deuterostomes?

Echinodermata and Chordata

What is the Cambrian Explosion?

A period around 530–500 million years ago when many major animal groups first appeared in the fossil record

Name two hypotheses proposed for the Cambrian Explosion.

Predator-prey arms race; rise in atmospheric and oceanic oxygen enabling more complex life (also linked to Hox gene evolution)