bio exam 4

Characteristics of animals

• multicellularity

• heterotrophic

• internal digestion

• movement

• no walls

• extracellular matrix (collagen & proteoglycan)

• cell junctions

• clustered Hox genes

• similar rRNA

Choanoflagellate ancestor

• animals are monophyletic

• individual choanoflagellate cells → specialization of function

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Protostomes

• spiral cleavage

• determinate cleavage

• blastopore becomes mouth

• ventral nerve aggregation (nerve cord on bottom)

Deuterostomes

• radial cleavage

• indeterminate cleavage (ex identical twins)

• bastopore becomes anus

• dorsal nerve aggregation (nerve cord on top)

• coelomate

• skeletal elements internal

Protostomes and deuterostomes

• bilateral symmetry

• tripoblastic

• Hox genes

• centralized nervous system

Bilateral symmetry

A single plane of symmetry through the anterior-posterior of an animal divides it into mirror image halves

Radial symmetry

Any plane of symmetry along the main body that divides the animal into similar halves

Acoelomate (flatworm)

• lack fluid-filled body cavity

• Ectoderm, mesoderm, mesenchyme, endoderm

Pseudocoelomate (roundworm)

• Fluid filled body cavity

• NOT completely lined mesoderm

• Internal organs

• Pseudocoel (cavity)

Coelomate (earthworm)

• Fluid filled body cavity

• Completely lined with mesoderm

• Internal organs

Segmentation

• improves movement

• allows specialization of body regions

• diversity correlates to diversity in Hox genes

Hox genes

• encode a family of transcription factors

• expressed in different combinations along an embryo

• determines fate of each segment

• evolutions tinkers with the “recipe” → genetic tool kit

Porifera (sponges)

• loosely organized animals

• some specialized cells

• no embryonic layers (true tissue, organs)

• no body symmetry

• mostly marine species

Sponge anatomy

• individual choanoflagellates form colonies and attached to sponge stalk

• sessile (stuck to the ground)

• water and food enter via ostia into atrium

• Chanocytes then feed off the food

• Water exits via osculum

Spicules

• made of silica or calcium carbonate

• serves as a structural support/skeleton

• captures prey

Spongin

• Tough protein used for connective elements

• protection/strucutre

Ctenophora (comb jellies)

• exclusively marine

• dipobastic

  • endoderm→gastroderm

  • ectoderm→epidermis

  • connected via mesoglea

• Bi-radial or rotational symmetry

• gastrovascular cavity

• tentacles around mouth

• nerve net

• plates of cilia (ctenes)

• bioluminescence

• two long tentacles

• colloblasts excrete a sticky substance to trap prey

• first complete gut (water/waste eliminated through 2 anal pores)

Cnidaria (corals, anemomes, jellyfish)

• genomic support

• distinct organ systems

• nerve nets

• gastrovascular cavity

• cnidocytes (stinging cells) (like a harpoon)

• nematocyst- stinging structure

Anemone and coral

• have dominant polyp stage

• polyps produced through sexual reproduction

Jellyfish

• have dominant medusa stage

• medusa produced through asexual budding of mature polyp

Anthozoans (cnidaria)

• polyp stage dominant

• tubular body w/ aboral end attached to substrate

• colonial or solitary

• examples: anemines, sea pens, corals, gorgonians

Hydrozoans

• diverse life cycles

• interconnected (colonial) polyps w/ continous gastrovascular cavity

• examples: Portuguese Man o’ war, hydra, by the wind sailor

Scyphozoans

• True jellies

• Medusa stage dominant

• all marine

Medusa

• mobile

• simple sense organs near bell margin

• statocysts: equilibrium

• ocelli: photosensitive

• asexual budding of medusae

Lophotrochozoans

Trochophore larva and/or lophophore (ciliary feeding device)

Lophopore

• circular/u-shaped ring of ciliated hollow tentacles around mouth

• food collection & gas exchange

• convergent evolution

Trochophore larva

• swim w/ cilia

• brings plankton to larva for food

• lost in many lineages

Phylum platyhelminthes (flatworm)

• lack specialized respiratory/circulatory system→breathe via diffusion

• incomplete digestive track

• muscular pharynx

• predatory or parasitic

Tubellarians (platyhelminthes)

• only free-living flatworm

• marine, freshwater

• ex. planaria

Cestoda-Tapeworms (platyhelminthes)

• no mouth or gut→absorb nutrients

• long ribbon of proglottids (sex organs)

• often needs 2 vertebrate hosts (human and animal)

Trematoda-Flukes (platyhelminthes)

• all parasites

• complex life cycles

• ex. schistosoma

  • inflammation & blockage of organs

  • liver, intestine, lung damage (or death)

Phylum annelida (segmented worms)

• specialization of segments @ anterior end

• respire across skin → moist/wet environments

• complete gut

• many body components repeated

• coelom acts as hydrostatic skeleton

• segments contract independently→ strong efficient movement

Hydrostatic skeleton

• provides support and shape

• used for locomotion and burrowing

Setae

stiff, hair-like bristles that help with movement and sensing

parapodia

paddle-like lateral appendages

Polychaeta-bristle worms (annelida)

• many hairs

• mostly marine

• setae & parapodia

Oligochaeta-earthworms (annelida)

• few bristles

• all hermaphrodites (male and female reproductive parts)

• important for soil conditions

Hirudinea-leeches (annelida)

• primarily freshwater

• fixed number of segments (32)

• anterior & posterior suckers

• secrete anti-coaguant (prevents blood from thickening)

Phylum mollusca (snails, squid, mussels, etc)

• 100,000 species

• foot, visceral mass, mantle, radula, open circulatory system (hemocoel)

Radula

tongue-like ribbon that serves as a feeding structure to break apart food particles before ingesting

Polyphacophora - chitons (mollusca)

• 8 plated shell

• marine omnivores

Bivalvia-clams, mussels, oysters (mollusca)

• two shells

• filter feeders (no radula)

• open circulatory system

• 30k species

Gastropoda- snails, slugs (mollusca)

• radula

• shell

• large foot

• open circulatory system

• herbivores, omnivores, predators

Cephalopoda-squid, octopus, nautilus (mollusca)

• fast-swimming predators

• mouth ringed by tentacles

• beak

• closed circulatory system

• highly cephalized

Ecdysozoan

synapomorphy: molting (shed rigid cuticle/shell)

Phylum nematoda (round worms)

• thick, multi-layered cuticle

• longitudinal muscles only (move differently from annelida)

• most abundant animal on Earth

• Many are parasites (ex. filariasis)

Filariasis

• Parasitic infection caused by nematodes

• Transmitted through mosquitos or flies

• damages lymphatic system

• causes severe swelling, fever, skin thickening

Arthropod relatives

• soft, unjointed appendages

• Tardigrades (water bearers)

• Onychophorans (velvet worms)

Phylum Arthropoda

• approx. ¾ of all described animal species

• rigid exoskeletons for muscle attachment

• jointed appendages

• segmented bodies

Subphylum Trilobita (arthropoda)

• among earliest arthropods

• first appearance of jointed appendages

• extinct

Subphylum Myriapoda (arthropoda)

2 body regions: head and abdomen

Centipedes (Myriapoda)- Arthropoda

• Fast moving carnivores

• one pair of walking legs per segment

Millipedes (Myriapoda)- Arthropoda

• Herbivores

• two pairs of walking legs per segment

• roll into coil

• eject toxin for protection

Chelicerata (Arthropoda)

• Head/thorax and abdomen

• Six pairs of appendages

  • chelicera (fangs)

  • pair of pedipalps

  • four pairs of walking legs

• Ex. spiders, scorpions, mites, ticks

Spiders (chelicerata)

chelicerae w/ venom from poison glands

Mites & ticks (chelicerata)

• Mites: free-living scavengers or pests on crops

• Ticks: all ectoparasites

Horseshoe crabs (chelicerata)

• Hemocyanin

• blue blood

• population decline

Sea spiders (chelicerata)

• uses legs to walk or swim

• many small species

Subphylum crustacea (arthropoda)

• dominant marine arthropods (copepods)

• head, thorax, abdomen

• specialized appendages

• more biomass than nematodes

Carcinization

example of convergent evolution where non-crab crustaceans independently evolve into crab-like form

Subphylum hexapoda (arthropoda)

• dominant terrestrial

• single pair of antennae + 3 pairs of walking legs

• unique gas exchange: tracheae

• insects and springtails

Insects (hexapoda; arthropoda)

• Most diverse animals

• Insect wings:

  • evolutionary success

  • outgrowths of body wall cuticle

  • retain walking legs (walk & fly)

• Insect mouth:

  • diversity

  • adapts to eat different types of food

Ecological importance of arthropod traits

• complex life cycles

• diverse feeding structures

• segmentation

• exoskeletons

Phylum echinodermata

• pentaradial symmetry as adults

• bilateral symmetry as larvae

• internal calcified skeletal elements

• water vascular system w/ tube for feeding, gas exchange, locomotion

• loss of pharyngeal slits

Water vascular system

• water into madreporite→ring canal→ampullae

• tube feet

  • movement

  • gas exchange

  • feeding

  • excretion

• no excretory organs = no osmoregulation only found in saltwater

Pedicellariae

• feeding

• defense

• cleaning

Phylum chordata

• dorsal hollow nerve cord

• post anal tail

• notochord (dorsal supporting rod)

Notochord

• single flexible rod between digestive tract and nerve cord

• fibrous tissue and fluid filled cells

• skeletal support

• in vertebrates, replaced by backbone during development

How do we know humans are chordates?

• We possess all of these characteristics (pharyngeal slits, notochord, post-anal tail) at some point during development, present in embryonic development

• Notochord→spine

• Pharyngeal slits→ear, tonsils

• post-anal tail→similar to tailbone

• dorsal hollow nerve cord→spinal cord & brain

Subphylums cephalochordates and tunicata (chordata)

• marine filter feeders

• mucous net & pharyngeal slits trap food

• cephalochordata= lanclets

• tunicata=tunicates

Vertebrates (chordata)

• rigid internal skeleton (cartilage or bone)

• anterior skull w/ large brain

• internal organs suspended on coelom

• well-developed circulatory system w/ ventral heart

Hagfish (class myxini)

• craniate: notochord & cranuim no vertebrate

• cartilage

• 3 small accessory hearts (weak circulation)

• lack eyes, jaws, fins

• slime

Lamprey (class petromyzontida)

• First vertebrate

• Lack jaws & appendages

• rudimentary vertebrate column

• migrate to spawn

• entirely parasitic as adults (sea)

• do not feed as adults (freshwater)

Gnathostomes

• Jawed fish

• paired fish provide stability and propulsion

Evolution of jaws

• allowed for feeding on diverse prey types →evolutionary diversification

• more sophisticated head and body strucutres

• 2 pairs of appendages

• 2 additional Hox gene clusters

Development of hinged jaws

• developed from pharyngeal arches

• gill arches became modified

Class chondrichthyes: cartilaginous fishes

• skeletons of cartilage

• flexible, leathery skin

• ex. sharks, stingrays

How do sharks maintain buoyancy without a swim bladder?

Through a massive oil-rich liver filled with low-density squalene (up to 25% of body weight)

Class actinopterygii: ray-finned fishes

• swim bladder for buoyancy

• operculum covers and enhances water flow over gills

• bony skeleton

• most covered by scales

• fins supported by thin, bony flexible rays → moved by interior muscles

• 32k species

Lobe-finned fishes

• paraphyletic if tetrapods not included

• jointed fins supported by skeletal extension of pectoral and pelvic areas→ moved by muscles within fins

• lungs→homologous to swim bladders

Buoyancy and gas exchange

• cartilaginous fishes

  • large oily liver

  • nearly continuous swimming and/or buccal pumping

• ray-finned fishes

  • swim bladder

  • operculum

How did tetrapod limbs develop?

• Evolved from the pectoral and pelvic fins

• Eustenopteron (fully aquatic, lobed) → tiktaalik (aquatic, lobed limbs intermediate) → acanthostega (semiterrestrial tetrapod)

Tiktaalik

• neck moved independently of body

• flattened skull w/ eyes on top

• lungs

• wrist and finger-like bones