BIO153H5 LEC 14-15 Animal body & development

3 Eukaryotic Kingdoms

1. Plantae

2. Fungi

3. Animalia (Metazoa)

Plantae

Photoautotrophs that fix CO₂ with water and sunlight

Fungi

Chemoheterotrophic decomposers that digest food outside their body and absorb nutrients

Animalia (Metazoa)

chemoheterotrophic hunters that internalize food for digestion

Similarities between kingdoms

all plants and animals as well as some fungi are multicellular

difference between animals vs. plants and fungi

• animals do not have cellulose, or chitin cell walls for structural support

• instead, animals secrete compounds like collagen for structural strength

• haploid, multicellular form does not exist for animals → life cycle almost exclusively dominated by multicellular, diploid adult phase

KEY feature of animals EXCEPT SPONGES

• digestive tract → bag in animal body that stores and digests food

• central to animal embryo

Gastrulation is the beginning of:

cell differentiation

ectoderm differentiates into (JSHTNG → “jishting”)

• jaws

• skin

• hair

• teeth

• nerves

• germ

endoderm differentiates into (ERRD TRACTS & L EPI)

EPITHELIAL SURFACES OF

• excretory,

• reproductive,

• respiratory,

• digestive tract

• liver

mesoderm differentiates into (SMCs)

• skeleton

• muscle

• circulatory system

• *NOT ALL ANIMALS HAVE A MESODERM

indeterminate cleavage

• the process of embryonic cell development in bilateral animals that welcome the possibility of the embryonic cells individually becoming completely different organisms if separated

• monozygotic twins are an example → division of an early-human embryo in two, resulting in two, independent fetuses

why dizygotic (fraternal) twins are/are not a result of indeterminate cleavage

• dizygotic twins occur when two separate eggs are fertilized independently, thus, the twins did NOT formerly arise from the same, early-human embryo

body plans & symmetry types

fundamental shapes/layouts of animal bodies

• radial symmetry

• bilateral symmetry

• asymmetry

radial symmetry

• body arranged around a single, top-down axis passing through the center of the body

• radiating body parts from the central axis

• equal interaction with the environment from all sides

organisms with radial symmetry

• sessile → living attached to a surface: hydra, sea anemone

• planktonic → drifting/weakly swimming: jellyfish

bilateral symmetry

• body parts arranged along two axes

  1. cranial-caudal (head-tail, respectively)

  2. ventral-dorsal (anterior-posterior, respectively)

• together, the axes form a plane that separates the left side from the right side in a symmetrical fashion

• animals with bilateral symmetry pack sensory equipment and CNS at the end of the head

organisms with bilateral symmetry

humans

• humans → palms are ventral, back of palms are dorsal

asymmetry & organisms

• sponges don’t have obvious symmetrical axes

• basal group of the animal kingdom that diverged the earliest from the rest of the animals

what do sponges/Porifera lack that makes them the basal group of the Animalia Kingdom

• true tissues → muscles and nerves

what do all Eumetezoa (non-sponges/Porifera) have in common

true tissues → muscles and nerves

are most animals vertebrates or invertebrates

95% invertebrates → only some Chordata members are vertebrates

two groups of Eumetazoa

1. Basal → radial symmetry (i.e., Cnidarians like hydra and jellyfish)

2. Bilateria (all other Eumetazoa)

major clades of Bilateria + basal group

• basal: Acoela

• major clades (dichotomies in order)

  1. Deuterostomia: Chordata, Hemichordata, Echinodermata

  2. Lophotrochozoa (polytomous descendants): Platyhelminthes, Rotifera, Ectoprocta, Brachiopoda, Annelida, Mollusca

  3. Ecdysozoa: Arthropoda, Nematoda

Deuterostomia groups (CHE dichotomies in order) & organisms

• Chordata

• Hemichordata

• Echinodermata

i.e.,

• starfish, human

Lophotrochozoa groups (PREBAM polytomous) & organisms

• Platyhelminthes

• Rotifera

• Ectoprocta

• Brachiopoda

• Annelida

• Mollusca

i.e.,

• clams, squids, snails, slugs, earthworms, tapeworms, flatworm like planaria, leeches

Ecdysozoa groups (AN) & organisms

• Arthropoda

• Nematoda

i.e.,

• crabs, spiders, nematodes, butterflies

Salpingoeca rosetta

• a colony-forming Choanoflagellate

• has proteins that can stick together

• its cells differentiate (colonial, individually-swimming) based on cues

• being studied to investigate multicellular animal origins

sponge characteristics

1. sedentary suspension feeders

   1. draws in water from side pores and erects from central cavity

   2. filters food particles in water

2. No highly differentiated tissues like eumetazoans

3. sponge body made of two layers of cells (epidermis and choanocytes) separated by mesohyl

   1. no need for circulatory system because they have adequate access to water

4. sponge has amoebocytes wedged into mesohyl so that the nutrients in by choanocytes can be transported throughout the sponge body

5. osculum is the opening of the cavity

parts of choanocytes

1. flagellum for drawing in water

2. collar projections around flagellum for capturing food

3. choanocyte (head) for phagocytosis

4. amoebocyte for circulation of nutrients throughout sponge body

vertebrate specific traits

1. backbone

2. hinged jaws

3. limbs with digits

why are there select exceptions to all Eumetazoa having differentiated tissues and digestive tracts?

• diverse morphology and physiology of Lophotrochozoa and Ecdysozoa that resulted in homologous and analogous traits, gain and loss of many traits

• this is why MOLECULAR PHYLOGENY IS BEST FOR DETERMINING ANIMAL LINEAGE

which group has the most body form diversity?

Lophotrochozoa

lophophores

ciliated feeding tentacles in some lophotrochozoans

trochophore larva

developmental stage that some lophotrochozoans go through

1. anus

2. mouth

3. atypical cilia tuft

which Bilateria group has a cuticle exoskeleton?

Ecdysozoa

• undergo moulting/ecdysis

which group has the most species-rich diversity?

Ecdysozoa

• more species than all other eukaryotes, combined!

most diverse phylum

arthropoda

second most diverse phylum

mollusca

arthropod classes & general characteristics

• crustaceans → mainly aquatic

• insects → mainly terrestrial

generally undergo moulting/ecdysis

why moulting is dangerous

• soft arthropods are vulnerable → new shells/skins might not be developed in time before predation

• i.e., soft-shell crabs are those that have a soft-shell right after moulting

what class co-evolved with angiosperms

• insects → nourished by nectar → pollinate flowers → mutualism

insect body plan

1. segmented

   1. head

   2. thorax

   3. post-genital region

2. usually one or two pairs of wings on the dorsal side of the thorax

   1. wings are cuticular extensions

3. can still have three pairs of legs while having wings

why insect wings are considered convergent evolution to bird species and non-insect, wing-bearing creatures

insects did not have to sacrifice legs to gain wings unlike birds and bats whose wings are modified limbs/forearms

incomplete metamorphosis & sample organisms

• several moults via metamorphosis before becoming the full, adult form

• could resemble adults but be smaller, lack certain traits like wings, etc.

• grasshoppers, praying mantises, lice, cockroaches, dragonflies

complete metamorphosis

• stepwise growth of larva into adult via pupal stage

  • pupal stage is what metamorphosis occurs, breaking down larval tissues and building new adult body

    • wasps, bees, butterflies, beetles, flies

• larval stages are specialized for eating and look completely different from adult

  • caterpillar, maggot

• adult is specialized for reproduction and dispersal

Arthropod body

1. segmented body with jointed appendages attached (making antennae, pincers, legs, etc.)

2. pair of compound eyes (multi-lens)

3. cuticle-coated body and joints

mollusc phylum characteristics

• snails, slugs, clams, octopuses, squids

• mostly marine, some freshwater and terrestrial

• soft-bodied

• calcium carbonate excretion to make shell (lost or internalized in other species, i.e., squids)

mollusc body characteristics

1. visceral mass → contains many internal organs

2. mantle → covers visceral mass and secretes shell

3. foot → for movement and attachment

mollusc mantle notable characteristcs

• may extend beyond visceral mass, creating a hollow mantle cavity

  • located in the mantle cavity are gills, the anus and excretory organs

bivalves physiology

• aquatic suspension feeders such as clams, oysters, mussels, scallops

• two shells connected by a hinge clamped shut by muscles

• gills used for feeding and gas exchange

  • incurrent siphon for inhaling water

  • excurrent siphon for exhaling water

  • gill trap food as water passes through

• low mobility → can flap valves to swim

cephalopods

• INVERTED bivalves

• aquatic hunters like octopus and squid

• mantle is on the outer surface (shells are minimized, internalized, or lost)

• foot evolved to tentacles and parts of the excurrent siphon

  • mantle contracts to eject water from the excurrent siphon and propel animal forward

  • muscular siphon can be pointed multiple directions

• draws water into mantle cavity through incurrent siphon

• chromatophores on the skin help with signaling and camouflage

nematodes

worms

• found in many moist habitats (tissues of plants and animals, body fluids, aquatic environments, soil)

• free-living, parastic

• i.e., Caenorhabditis elegans, Trichinella spiralis

Caenorhabditis elegans

• adults have 959-1033 cells (gender-dependent)

• developmental pathways and locations of all cells have been mapped

• really useful for developmental biology and medical research

Trichinella spiralis

parasite found in muscles of pork