Animal characteristics:

1. Multicellular eukaryotes

2. Cells specialized for specific functions.

• Cell -> Tissue -> Organ
• simple, small animals use diffusion for gas exchange, circulation, waste disposal
• Larger animals need organs systems for these functions

3. Heterotrophs: ingest food and digest it inside body (fungi digest outside)

4. Most move: sponges have motile larvae and sessile adults

5. Most have nervous and muscular systems to respond to stimuli in environment

6. Most diploid

• Sexual repro has large, nonmotile egg and small, flagellated sperm
• Egg+sperm -> zygote
• Zygote divides by mitosis (cleavage)
• Enough cells form blastula, hollow ball of cells
• Blastula ball goes through gastrulation: cells segregate into tissue germ layers
• Some go through larval stage (sexually immature, may look different) before forming adult.
• Larvae metmorphosize into adult (change form)

Vertebrates have backbone (vertebrae), fewer than 5% animals. Invertebrates lack backbone.

Depend on producers for raw materials, energy, oxygen. Depend on decomposers to recycle nutrients

Animals probably evolved in shallow Precambrian seas, most animals still live in SW.

• Most salt water isotonic to animal tissue fluid (easier fluid and salt balance)
• SW bouyancy supports body
• SW stable temp
• Plankton (animals and protists suspended and floating in water) = ready food
• Cope with water movement as swimmers, sessile, burrowers, plankton

Freshwater (FW) is hypotonic to tissue fluids of most animals

• Water moves into animal cells
• Cell salts tend to move out into water for osmotic balance.
• Osmoregulation is balancing water and salt content of cells. Takes energy
• Less food than in SW
• Oxygen and temp, trubidity (cloudiness), volumes vary widely

Land = dessication

• temp extremes
• some arthropods (insects, spiders) and some vertebrates successful on land. All other groups of animals do better in SW.

Animals divided into 2 big groups:

1. Parazoa = sponges

• Phylum Porifera
• Function like colonial, unicell protista
• Probably evolved from collared flagellated protista
• Cells versatile, can change functions
• No True Tissues

2. Parazoa = all other animals with true tissues.

Symmetry = arrangement of body dtructures in relation to axis of body.

1. Assymetrical = no symmetry, most sponges

2. Radial symmetry: body has form of wheel or cylinder

• multiple planes thru center axis will give mirror images
• Cnidaria (jellyfish, anemones) Adult Echinoderms (star fish, etc)
• Receive stimuli well from all directions
• Modified radial symmetry = biradial symmetry. Sea Anemones and comb jellies have bodies that can only be divided into similar halves by 2 planes.

3. Bilateral symmetry: can be divided by only one plane thru body midline to give roughly mirror right and left images.

• Most animals
• Adaptation to locomotion: head finds stimuli first
• Nervous and sensory organs concentrated in head.

Vocabulary

• Dorsal = back surface (dolphin dorsal fin)
• Ventral = underside, belly
• Anterior = towards head
• Posterior or caudal = toward back, tail end
• Medial = toward midline
• Lateral = toward side, away from middle
• Cephalic or superior = head end of body, above
• Inferior = below, toward feet.

Bilateral symmetry has 3 axes:

1. anterior-posterior from head to tail

2. Dorsoventral from back to belly

3. Left-right axis from side to side

• Sagittal plane divides body into right or left parts, from anterior to posterior and dorsal to ventral. Cuts along the length of your nose
• Frontal plane divides into dorsal and ventral . Cuts through your ears
• Transverse section or cross section separates into anterior and posterior. Cuts at your waist to head and feet.

Most animals develop from 3 germ layers.

1. Outer Ectoderm = epidermis covering body, nervous system

2. Inner Endoderm = lines digestive tube, and other digestive organs.

• cnidarians and ctenophores only develops these 2 layers, are diploblastic
• All other animals have 3 germ layers, are triploblastic.

3. Middle Mesoderm = muscles, bones, circulatory systems.

Body cavity: a fluid-filled space between the body wall and digestive tube.

• Triploblastic animals
• Tube within a tube bldy plan
• Body wall is outer tube from ectoderm
• Inner tube = digestive tube or gut, lined with tissue derived from endoderm, open at mouth and anus
• Cavity = space between the tubes.

1. Acoelomates: solid body, no body cavity

• Flatworms like planaria
• Nemerteans

2. Pseudocoelomate: false body cavity.

• False = cavity not completely lined with mesoderm
• Nematode roundworms and rotifers

3. Coelomate: true coelom = body cavity completely lined with mesoderm

• peritoneum and mesenteries are the lining tissues derived from mesoderm
• mollusk, annelid, arthropod, echinoderm, hemichordate, chordate.

2 main evolutionary lines of coelomates:

• In gastrulation, some cells move inward to from the embryonic gut.
• Gut opens to outside in hole called blastopore.
• Difference in evolution is what happens to blastopore.

1. Protostomes

• Blastopore usually becomes mouth
• Spiral cleavage: cell divisions diagonal to polar axis
• Determinate cleavage: development of each embryonic cells fixed early. If you separate one of the 4 first cells, makes 1/4 of larva.
• Schizocoely: Coelom formed by mesoderm splitting, widening. Schizocoelomate animals.

2. Deuterostomes

• Blastopore becomes anus and second opening becomes mouth
• Radial cleavage: early divisions parallel or right angles to polar axis, cells directly above and below one another.
• Indeterminate cleavage: no set fate for early cells. If you separate one cell from first 4, cell will make complete, small larva. Identical twins.
• Enterocoely: mesoderm outpockets pinch off and form pouches. Enterocoelomate animals.

Sponges: Phylum Porifera

• Bodies have tiny holes to let water through
• Aquatic, mostly marine
• Many asymmetrical: flat crusts, balls, cups, fans, vases
• Some have bright color from symbiotic bacteria or algae. Others drab.
• Probably evolved from choanoflagellates: protozoa with one flagella surrounded by collar of microvilli. Sponges have collar cells that are very similar, move water currents through sponge.
• Parazoa: no true body tissues

Sponge Classes divided by skeleton they secrete:

1. Class Calcarea: chalky skeleton of small CaCO3 spicules

2. Class Hexactinellida = glass sponges with 6-rayed silicon spicules.

3. Demospongiae = variable skeletons

• most sponges
• fibrous protein spongin, silicon spicules, both.

Water flow:

• Water enters hundreds of tiny ostia (pores)
• Water passes into central cavity (spongocoel)
• Water flows out through opening, osculum.

Eating:

• Body wall extensively folded, complicated canals increase surface area for food capture.
• No definite tissues, but division of labor: nutrition, support, contractoin, reproduction.
• Epidermal cells outer layer and line canals
• Porocytes = tube cells that regulate size of pore by contracting.
• Collar cells in inner layer create water currents. Collar = microvilli extension of cell membrane, also flagellum.
• Water brings in food, O2; brings away CO2, waste, food not digested back out osculum.
• Collar cells trap food in collar, phagocytize food
• Suspension feeders: trap and eat whatever food water brings
• Gas Exchange and excretion of waste by diffusion of individual cells.

Mesohyl = gelatin layer between inner and outer layers

• support from skeletal spicules
• amoeboid cells mov thru mesohyl, transporting and digesting food.
• Other amoeboid cells secrete spicules.

Cells can react to stimulus, no specialized nerve cells. Behavior = capturing food, regulating water flow.

Reproduction:

• Larvae flagellated, swim.
• Adult sessile: attached to solid surface, no locomotion
• Asexual reproduction: bud breaks off parent. Colony if bud doesn’t detach
• Sexual repro: most hermaphroditic, one individual makes eggs and sperm, but at different times to cross-fertilize
• Some amoeboid cells become egg or sperm
• Sperm shed into water, taken in by other sponge
• Sperm gets into mesohyl, fertilization and early development inside mesohyl
• Embryo larva eventually leaves parent by spongocoel, swims, then settles down.

Regenate to repair injury. If you separate cells of sponge in lab, cells recognize each other and reaggregate in proper place, reforming sponge.

Phylum Cnidaria:

• radial symmetry
• cnidocyte = specialized stinging cell
• solitary or colonies (corals, Portugese man of war)

Body = hollow sac with mouth and tentacles at one end.

• Gastrovascular cavity = digestion, water as circulation for waste, gases
• Mouth is only opening, so waste also leaves by mouth, if not by diffusion.

Diploblastic: 2 definite tissue layers

1. Ectoderm becomes epidermis = protection

2. Endoderm becomes inner gastrodermis = digestion

• Layers separated by gel mesoglea

2 body shapes:

1. Polyp (Hydra)

• Long body with tentacles at one end, like upside down, long jellyfish

2. Medusa (jellyfish)

• bowl shape
• mouth on lower, concave oral surface
• aboral, convex upper surface like curve of bowl
• Portugese man of war colony has both medusa and polyp forms.

First animals with true nerve cells

• form irregular nerve nets
• connect sensory cells in body wall with contractile and gland cells.
• Impulse goes in all directions equally, no one direction.

1. Class Hydrozoa: hydra, Obelia, Portugese man of war

Hydra in fresh water , easily regenerates

• sessile attached to rock or plant by disc cells in base
• mouth at other end, surrounded by tentacles used in feeding
• Body = outer epidermis for protection; inner gastrodermis for digestion
• Contractile cells in both layers, so bends, short, lengthen
• water in cavity = hydrostatic skeleton for muscles to work against.
• Cnidocytes in epidermis, especially tentacles. Nematocyst releases coiled thread to catch prey
• Tentacles push food into mouth
• Digestion in GV cavity, gastrodermal cells take up bits of food into food vacuoles
• Gas Exchange and excretion by diffusion, motion helps move
• Reproduce asexually by budding, differentiate into male and female. After fertilization, zygote can be covered with shell for protection, leaves parent

Colony forms by budding and staying attached. Some individuals specialized for feeding, repro, defense

Some cnidarians alternate between sexual and asexual repro, both diploid.

Obelia life cycle: have feeding and asexual repro polyps

• freeswimming male and female medusae bud off repro polyps
• Medusae produce sperm and eggs, fertilization
• Zygote develops inot ciliated swimming planula larva
• Planula then attaches to surface, starts new generation of polyps by asexual repro.

2. Class Scyphozoa: jellyfish

Medusa stage predominant

• thick, viscous mesoglea that firms body
• polyp small, may be absent in jellfish

3. Class Anthozoa: sea anemones, corals

• individual or colonial polyps
• no freeswimming medusa stage
• Polyp makes eggs and sperm, zygote becomes small, ciliated planuls larva that may swim
• Gastrovascular cavity partially divided into connected chambers with vertical partitions that increase surface area for digestion
• Corals can capture prey, most have zooxanthellae = photosynthetic algae living within cells of coral digestive cavity. Mutually beneficial: Coral gets O2, carbon and nitrogen compunds. Algae gets ammonia from coral, used to make nitrogenous compounds.
• Coral communites very productive ecosystems: lots of species diversity with complex food webs
• Coral is barrier against waves, so protect islands, shoreline
• Only uppermost reef is living, built on billions of layered cells
• Overfishing, mining, pollution, silt from land runoff, too many recreational divers killing reefs

Phylum Ctenophora = comb jellies

• Marine, fragile, luminescent
• Biradially symmetrical : equal halves from cutting along 2 axes
• 2 cell layers separated by think mesoglea
• Outer surface has 8 rows of cilia (combs)
• 2 long tentacles have adhesive cells that trap prey, but no stinging nematocysts.

Bilateral Symmetry

Phylum Platyhelminthes = flatworms

Acoelomate!

Characteristics

1. Bilateral symmetry with cephalization: concentration of sense organs in hed

2. Triploblastic: 3 definite tissue layers. Endoderm, epiderm and mesoderm

3. Well-developed organs

• Organ = functional structure made of 2 or more kinds of tissue
• Pharynx for taking in food
• simple brain, eyespots, other sensory organs in head
• System for excreting waste and maintaining fluid balance
• Complex reproductive organs

4. Simple nervous system

• Brain = 2 masses of nervous tissue = ganglia, in head region
• some have 2 long nerves along body, cross nerves between 2 long nerves

5. Protonephridia: organs that function in osmoregulation and excretion of metabolic wastes.

6. Gastrovascular cavity: only one opening = mouth, but digestive system highly branched to increase surface area for digestion and absorption

No organs for circulation or gas exchange: diffusion

Parasitic flukes and tapeworms have hooks or suckers to hold onto host

• bodies resist digestive enzymes.
• complicated life cycles
• produce LOTS of eggs
• some have lost sensory organs and digestive system, the host digests food and parasite absorbs simple compounds into body.

Class Turbellaria = free living planaria

• SW, FW, tropical terrestrial forms
• Planaria have auricles for chemoreception to locate food.
• Carnivorous, trap small animals in mucous secretion
• one opening to dig. tract = mouth
• pharynx projects out thru mouth to grab food
• Branched GV cavity = extracellular digestion with enzymes secreted by gland cells
• undigested food goes back out thru mouth
• Digestible food distributed thruout body by diffusion.
• Flat body, so gases, most waste diffuse in and out
• Protonephridia excrete some metabolic waste. Blind tubes end in flame bulbs. Beating cilia move waste into tubules and out of body.
• Capable of learning, memory thruout nervous system
• Reproduce asexually: divides along middle into 2 planaria
• Sexual repro hermaphroditic: have both male and female organs. 2 planaria exchange sperm that fertilize each other’s eggs in cross-fertilization.

Class Trematoda and Monogenea = flukes, parasites

Hooks and suckers attach to host. Complex, prolific repro organs

Blood fluke Schistosoma in tropical areas

• Free swimming larva (cercaria) burrows thru human skin, go to circulatory system
• Male and female permanently paired, mate in human intestinal vein
• Eggs pass into intestine, leave body with feces
• Eggs hatch in FW to free swimming larva (miracidia)
• Larva burrows into aquatic snail, develops into asexually reproducing form. Snails in rice paddies, ponds, marshes
• Cercariae larvae leave snail, into water, find more humans

Liver flukes common in Asia, also complicated life cycle with intermediate fish hose

Class Cestoda = tapeworm intestinal parasites

• 5000 different species, live in every kind of vertebrate hose
• long, flat, ribbon-like
• Scolex (head) has suckers and hooks to latch onto host (Fig 28-15)
• Body = chain of segments called proglottids
• Each proglottid = male and female repro parts, 100K eggs
• Proglottids farthest from head = ripest eggs, shed with feces
• No mouth or digestive system: host digests food and tapeworm absorbs simple comounds into body
• No well-developed sense organs

Beef tapeworm: larva encysted in muscle tissue of cattle

• You eat raw or rare infected meat, digestion breaks down cyst, larva released
• Larva attaches to intestinal lining, matures
• Sexual repro within human intestine, shed proglottids filled with zygotes.
• Eggs ingested by cattle that eat grass, etc contaminated with human feces
• Eggs hatch in cow intestines, travel to muscle and encyst.

Pork tapeworm, fish tapeworm also species specific for humans.

Phylum Nemertea = ribbon worms

• Most SW, some FW or land
• Long narrow body, either flat or cylindrical. Bilateral symmetry
• Bright colors: orange, red, green, black with color stripes.
• Proboscis = long, hollow muscular tube that can be extruded from anterior end to get food or in defense
• Proboscis secretes mucous to trap prey
• Functionally acoelomate, but coelomic cavity surrounds proboscis (on the evolutionary road to coelomates)
• Also important in evolution: circulatory system of blood vessels, no heart.
• Digestive tract as complete tube with 2 openings.

Pseudocoelomate

Phylum Nematoda = roundworms

• Vital to decomposition and nutrient recycling.
• Soil, FW, SW
• Thrash around from contraction of longitudinal muscles.
• Some freeliving
• Parasites = Ascaris, hokkworms, pinworms, trichina worms, filarial worms
• Body is elongate, cylindrical, tapered at both ends, covered with cuticle to resist dessication.
• Fluid-filled psuedocoelom= hydrostatic skeleton for muscles to work against.
• Movement = nutrient transport, distribution
• Bilateral symmetry
• Complete digestive tract
• 3 complete tissue layers and definite organ systems
• lack circulatory structures,
• sexes usually separate

Ascaris = human intestinal parasite

• sexes separate, mate in human intestine, 200K eggs/day, leave with feces
• Eggs in soil, on unwashed veggies, fruit, hands
• Eggs hatch in intestine, larvae burrow into blood or lymph vessels
• TO heart, lungs, break into air passage to throat, swallowed. Damage tissues.
• Larvae thru stomach to intestines, settle, feed, mature.
• Abdominal pain, malnutrition, allergic reaction, block intestines

Hookworm live in human intestine

• Eggs leave body with feces
• Larvae hatch, feed on bacteria in soil
• Mature, infective, burrow through bare skin to blood.
• Migrate through body to intestine
• Tissue damage and loss of blood

Trichina worms live in pigs, rats, bears

• Humans eat undercooked meat
• Live in small intestine of host
• Females produce larvae, migrate thru body to skeletal muscle and encyst
• Must be eaten by another mammal; in humans, calcified cysts cause muscle pain

Pinworms in kids

• Eggs ingested on dirty hands
• Adult worms live in large intestine
• Females migrate to anal region, shed eggs at night: Itchy, so eggs in air, house
• Can cause intestinal wall injury.

Phylum Rotifera = rotifers

• Microscopic, but multicellular aquatic animals
• Most FW, some SW, damp soil
• Crown of cilia on anterior end looks like rotor moving as it beats water
• Pseudocoelomates
• Complete digestive tract, tiny food ground by muscular organ after mouth
• Nervous system with "brain", sense organs, eyespots
• Protonephridia with flame cells for waste removal
• Cell constant: each member of species has exactly the same number of cells, each part of body has exactly same number of cells in characteristic pattern.

E-mail me at eott-reeves@acmail.blinn.edu or go back to my homepage.