Lecture 10 -- Intro to Animals and Animal Characteristics

What is the common ancestor of all animals?

choanoflagellates which are single-celled protists

What is the most ancestral animal?

Sponges

What do sponges lack that other animals don't?

true tissues

What are choanocytes?

specialized cells that allow for filter feeding

What are general animal characteristics?

- animals are multicellular, most have tissues, organs, and organ systems
- all are aerobic heterotrophs (obligate aerobes)
- most go through sexual reproduction
- all have mobility at some stage of life
- all lack cell walls

What is the difference between vertebrates and invertebrates?

Vertebrates: they are derived meaning later in evolutionary time
- include mammals, birds, reptiles, amphibians, fishes, etc.
Invertebrates: they are basal meaning earlier in evolutionary time
- make up over 90% of the known species of animals
- arthropods are the most diverse

What is radial symmetry?

infinite lines of symmetry (same on all sides) which comes from the basal form
- ex. jellyfish, starfish

What is bilateral symmetry?

one line of symmetry which comes from the derived form
- ex. birds, insects, mammals

What are the different body regions of a bilateral animal?

Anterior: towards the head
Posterior: towards the tail
Dorsal: towards the upper part or back of the standing animal
Ventral: towards the lower part or belly of the standing animal

What is cephalization?

the gradual concentration of sensory organs to the head and close to the central nervous system

How are animals classified through embryonic development?

1. starts out as a zygote which then undergoes cleavages which allows for mitosis so it can rapidly divide and grow
2. continues to cleave until it forms the blastula which is a hollow ball known as the blastocoel
3. the blastula eventually grows and develops itself into layers and pockets--this entire structure is known as the gastrula which has a cross section and is formed through gastrulation

What are the different layers of the cross section (from innermost to outermost)?

archenteron --> endoderm --> blastocoel --> ectoderm

What us evagination?

the formation of the archenteron

What are the different tissue layers of an animal?

Ectoderm: start of the tissue that lines the body surface
- i.e. sensory organs, skin, nervous system, enamel
Endoderm: develops into the gut lining
- i.e. the digestive tract lining, liver, pancreas
Mesoderm: source of muscles and support structures
- i.e. bones/skeleton, circulatory system, kidney, spleen, genitals

What is the difference between diploblastic and triploblastic?

Diploblastic: has two germ tissue layers--ectoderm and endoderm
Triploblastic: has three germ tissue layers--ectoderm, mesoderm, and endoderm

What is a coelom and its function?

a fluid or air filled space located between the digestive tract and the outer body wall
- the function is to prevent injury to internal organs and enables organs to grow and move independently of the outer body wall
- ALL animals have a coelom

What is a coelomate?

a true coelom that forms from the mesoderm
- all vertebrates and most invertebrates

What is a pseudocoelomate?

coelom only partially lined with mesoderm
- ancestral to coelomates

What are acoelomates?

they lack a coelom meaning their organs are connected to the body wall
- the most ancestral coelomates
- these animals don't grow very tall because their body wouldn't be able to support the proportions

What are the two trajectories of early embryological development?

Protostome (ancestral) and Deuterostome (derived) development

What characterizes protostome development?

- Cleavage: at the 8 cell stage cells divide in a spiral, circular motion around the polar axis
- Determination of the earliest cells: the cells are determinate meaning as they are dividing they already have an assigned function in the body
- Coelom: there are solid masses of the mesoderm the split apart to form the coelom
- Fate of the blastopore: will end up becoming the mouth of the organism

What characterizes deuterostome development?

- Cleavage: at the 8 cell stage cells divide in a radial motion, toward the polar axis
- Determination of the earliest cells: cells are indeterminate meaning they ave not been assigned a role for specific functions
- Coelom: folds of the archenteron end up becoming the mesoderm which then ends up forming the coelom
- Fate of the blastopore: will end up being the anus of the animal

What are the evolutionary characteristics between animals?

1. All animals share a common ancestor
- i.e. choanoflagellates
2. Sponges are the most ancestral animals
- look very similar to choanoflagellates
3. Eumetazoa: refers to all animals with tissue (everything except sponges)
- Metazoa: all animals
4. most animals demonstrate bilateral symmetry
5. Chordates (includes all vertebrates and some invertebrates) and Echinoderms (very simple animals like urchins, starfish, etc.--closest relative to chordates) are deuterostomes