Chapter 27: Animal Diversity

BSC2011C Fall '25

When and where did animals first appear?

600 mya; Ocean

About how many extant animal species are identified?

1 million

About how many extant animal species are not identified yet?

3-30 million

What are plesiomorphic character(s) animals share with prokaryotes?

Metabolism, plasma membrane, ribosomes

What are synapomorphic character(s) animals share with plants?

Sexual reproduction, meiosis

What are synapomorphic character(s) animals share with fungus?

Heterotrophy

What are heterotrophic animals?

Animals who cannot make their own food and have to feed on organisms (dead or alive)

What are the different types of heterotrophs?

Carnivores, herbivores, omnivores, parasites

What makes an animal, an animal?

Motility, complex tissue structure with specialized tissue types, diplontic life cycle, embryonic developmental stages

What makes an animal character autapomorphic?

New derived characters, not present in LUCA, prokaryotes, protists, fungus or plants

Are all animals fully motile?

No, some may only be motile for part of their life cycle

What phase of the diplontic life cycle is multicellular?

Diploid

What phase of the diplontic life cycle is unicellular?

Haploid

What is the diplontic life cycle?

A diploid multicellular organism produces haploid gametes through meiosis

Animals are said to have a ____ body plan.

Fixed

Some invertebrates don’t have tissues, just ____ cells

Specialized

What are differences between animal cells/tissues to plant tissues and fungal tissues?

No cell wall, gap junctions for communication between cells, sometimes embedded in extracellular matrix, connective tissue for structural support (vertebrates), epithelial tissue over external body and internal organs

What type of cells are included in connective tissue?

Non-living (extracellular matrix) and living cells

What does the connective tissue do?

Supports body structure

What tissues are the ones that not all animals have?

Connective, epithelial, nervous

What does epithelial tissue do?

Covers and protects internal organs and external body structures

What does muscle tissue do?

Facilitates movement

What are the types of muscle tissue?

Skeletal, cardiac, smooth

What does the nervous tissue do?

Receives and transmit electrical pulses

What are the types of nervous tissue?

Neurons and nerve cells

What are examples of specialized system functions?

Obtaining food/avoiding becoming food, finding a sexual partner, sensing environment/responding to it, motility

What are all the bodily systems?

Digestive, sensory, nervous, muscular, skeletal

What are the five monophyletic clades to the animal kingdom?

Ctenophora, Porifera, Placozoa, Cnidaria, Bilateria

What are Porifera?

Sponges

What are placozoa?

Parasitic amoeba-like animals

What are Ctenophores?

Comb Jellies

What are Cnidaria?

Jelly fish and relatives

What are Bilateria?

Animals with bilateral symmetry during embryo development

What are the two categories to animals?

Invertebrates and vertebrates

What are invertebrates?

Animals with no backbone

What are vertebrates?

Animals with a backbone

What’s the only animal kingdom clade that includes both vertebrates and invertebrates?

Bilateria

Aside from the presence of a backbone, what are other ways animals are classified?

Body plan and embryonic development

What is a body plan?

How body parts are distributed along an axis or axes

What does body plan mainly focus on?

Body symmetry

What are the three major body plans?

Asymmetrical, radial symmetry, bilateral symmetry

What does embryonic development focus on?

Number of germ layers, presence/absence of internal body cavity, origin of mouth and anus

What part of the diplontic life cycle are somatic cells?

Diploid phase (multicellular)

What part of the diplontic life cycle are gametes?

Haploid phase (unicellular)

What group of animals are an exception to the diplontic life cycle and how?

Insects; bees, ants, and wasps have males with haploid somatic cells

Can all animals reproduce sexually?

Yes

Can all animals reproduce asexually?

Yes, some can

What happens in sexual reproduction in animals?

Haploid sperm and haploid eggs are created via meiosis, sperm fuses with egg and results in a diploid cell (zygote)

What does the zygote go under via mitosis?

Cleavage

What happens when the zygote undergoes cleavage?

Cells divide into smaller and smaller cells

(Cleavage) Three mitotic divisions result in _____-___ __________

Eight-cell blastomere

Zygote cleavage continues and cells rearrange to create what?

Hollow blastula

What does continued cell division and rearrangement lead to?

Gastrulation

What is gastrulation?

Formation of archenteron and embryonic germ layers

What is archenteron?

Gut cavity

What are the embryonic germ layers?

Ectoderm, endoderm, and mesoderm

What part of the embryonic germ layer do all animals don’t have?

Mesoderm

All animals share ____ morphology and development

Embryonic

What determines embryonic development?

Homeotic genes

What are the DNA sequences in homeotic genes called?

Homeobox (Hox) genes

What do hox genes do?

Encode protein transcription factors

What are protein transcription factors?

Enzymes that facilitate transcription of mRNA

What do Hox genes determine?

Animal body plan

What is a nickname for Hox genes?

Master control genes

What are some examples of things the animal body plan determines?

Head/tail directionality, number of body segments, number/location of appendages

Why can Hox genes turn other genes on and off?

They encode for transcription factors that control the expression of other genes

Are Hox genes homologous or analogous?

Homologous

What clades don’t have Hox genes?

Ctenophora and Porifera

What does it mean for genes to be homologous?

Same chromosomes on the same locations

What does the Hox gene order determine?

Anterior/posterior axis, dorsal/ventral axis, body segments, appendages

How many duplication events do Hox genes undergo?

2-4

What do the additional Hox genes do?

Allows more complex body types

Invertebrates have how many sets of Hox genes?

One

Vertebrates have how many sets of Hox genes?

Four

Ctenophora and Porifera are considered ___ animal lines

Basal

Recent research shows what clade as the oldest of all animals?

Ctenophora

How many Hox genes do Placozoa have?

One

Some animals are ____ or ____

Diploblastic; Triploblastic

What does diploblastic mean?

Has two germ layers and consists of asymmetrical and radial symmetrical animals

What are the two germ layers in diploblastic animals?

Ectoderm and endoderm

What does the ectoderm layer do?

Covers surface of animal

What does the endoderm layer do in diploblastic animals?

Forms wall of digestive tract

What does triploblastic mean?

Has three germ layers and bilaterally symmetrical animals

What are the three germ layers in triploblastic animals?

Ectoderm, endoderm, mesoderm

What does the endoderm layer do in triploblastic animals?

Forms digestive tract, respiratory tract, urinary tract

What does the mesoderm layer do?

Forms muscle, bone, circulatory system and more

What animal clades are asymmetrical?

Porifera, Placozoa

What animal clades don’t have true tissues?

Porifera, Placozoa

How many cell types does Placozoa have?

Four

How many cell types does Porifera have?

Twelve

What does radial symmetry mean?

Body parts are arranged from a central point

What sides does radial symmetry have?

Top (oral) and bottom (aboral)

How do radially symmetrical animals receive information?

From all directions

What do radially symmetric animals DON’T have?

Head, tail, cephalization, directional movement

What clades are radially symmetric?

Cnidarians and Ctenophores

What does bilateral symmetry mean?

Single plane divides body to left and right sides that are mirror images

What do bilaterally symmetric animals have?

Head, tail, cephalization, streamlined motion, directional movement

What does cephalization mean?

Organized nervous system at anterior (head) end

What is a coelom?

Internal body cavity from mesoderm tissue

What does the coelom do?

Provides cushioning to internal organs, allows for body flexibility