Chapter 28 An Introduction to Animal Diversity

Characteristics of Most Animals 1. multicellular eukaryotes 2. cell specialization –(cells  tissues  organs) 3. heterotrophs 4. locomotion (sometime in lifecycle) 5. nervous + muscle systems (stimuli) 6. sexual reproduction –(large, nonmotile eggs; flagellated sperm)

Marine Environments Advantages –Buoyancy – support –Temperature – stable –Fluid + salt balance easily maintained Challenges –Water movement/currents Adapt: –Strong swimmer – squid, fish, mammals –Sessile –Burrow in sand/silt –Small body size  plankton (food supply around as tossed)

Other environments - problems Fresh water –Water hypotonic to animal fluids  Osmoregulation - pump out water, keep salts (ATP) –Less constant –Less food –Oxygen and temp. vary –Turbidity + water volume change

Land –Desiccation Adapt: body covering; respiratory surface deep within animal –Reproduction (desiccation) Adapt: internal fertilization; shells on eggs; embryo in mom –Temperature extremes

Body Symmetry 2 types –Radial wheel or cylinder form Spokes from central axis –Cnidarians – jellyfish, sea anemones –Echinoderms – sea stars –Bilateral Right and left halves – mirror images

Fig (a) Radial symmetry (b) Bilateral symmetry

Types of Body Cavities Coelom = fluid-filled space between body wall and digestive tube Acoelomate –No body cavity Pseudocoelomate –Body cavity, not lined with mesoderm Coelomate –Body cavity completely lined

Fig Zygote Cleavage Eight-cell stage Cleavage Blastula Cross section of blastula Blastocoel Gastrulation Blastopore Gastrula Archenteron Ectoderm Endoderm Blastocoel

Fig Coelom Body covering (from ectoderm) Digestive tract (from endoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) (a) Coelomate Body covering (from ectoderm) Pseudocoelom Digestive tract (from endoderm) Muscle layer (from mesoderm) (b) Pseudocoelomate Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) (c) Acoelomate

2 Main Groups of Coelomates Protostomes –“first, the mouth” –Mollusks, annelids, arthropods Deuterostomes –“second, the mouth” Echinoderms, chordates

Protostomes vs. Deuterostomes Cleavage Protostomes –Spiral Deuterostomes –radial

Fig. 32-9a Eight-cell stage (a) Cleavage Spiral and determinateRadial and indeterminate Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates)

Protostomes vs. Deuterostomes Developmental Fate of the Embryo Protostomes –“determinate” cleavage –Fixed early –Can only become certain cell types Deuterostomes –“indeterminate” cleavage –Can adapt to become another cell type

Fig. 32-9b Coelom Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (b) Coelom formation Key Ectoderm Mesoderm Endoderm Mesoderm Coelom Archenteron Blastopore Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom.

Protostomes vs. Deuterostomes Blastopore = (opening from outside to gut) Protostomes –Develops into the mouth Deuterostomes –Develops into the anus –Later, 2 nd opening makes mouth

Fig. 32-9c Anus Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Anus Mouth Digestive tube (c) Fate of the blastopore Key Ectoderm Mesoderm Endoderm Mouth develops from blastopore.Anus develops from blastopore.

Sponges – Phylum Porifera “to have pores” Bodies – tiny holes Marine

Fig. 33-3a A sponge

3 main classes of sponges Calcarea –Chalky, calcium carbonate spikes (spicules) Hexactinellida (glass sponges) –6-rayed spicules with silica Demospongiae –Variable Fibrous protein = spongin Silica OR spongin + silica

Fig Azure vase sponge (Callyspongia plicifera) Spongocoel Osculum Pore Epidermis Water flow Mesohyl Choanocyte Flagellum Collar Food particles in mucus Choanocyte Amoebocyte Phagocytosis of food particles Spicules Amoebocytes

Sponge Anatomy Spongocoel –Central cavity – water flows Ostia –Tiny pores, water enters Osculum –Open end, water exits Epidermal cells –Outer layer, line canals

Sponge Anatomy Canals –SA – food capture Porocytes –Tube like cells – form pores –Regulate diameter by contracting Collar cells

Sponge Anatomy Collar cells –Inner layer –Create water current, bring food and water to cells, carries away waste and CO2 –Trap and phagocytize food –Tiny collar at base of flagellum

Sponge Anatomy Mesohyl –Gelatin-like layer –Between inner and outer layers of sponge body Amoebocytes –In mesohyl –Digestion, food transport, secrete spicules

Sponge Feeding Suspension feeders –Trap + eat whatever food the water brings –Water circulates in body –Food trapped on sticky collars of choanocytes –Food digested in collar or amoeboid cell –Undigested – out to water through osculum

Gas exchange/Excretion Diffusion – in/out of individual cells

Response to Stimuli No special nerve cells – can’t react as a whole Individual cells can respond

Reproduction of sponges Asexual –Fragment or bud Sexual –Hermaphrodite – egg + sperm –Some amoeboid cells become sperm, some eggs –Eggs/sperm made at different times  cross fertilize –Sperm released into water, taken in by other sponges of same species –Fertilization and early dev. In mesohyl –Embryo moves to spongocoel, leaves with water –Swims, attaches to solid object  sessile

Cnidarians – Phylum Cnidaria marine Solitary colonies

Fig. 33-3b A jelly

3 classes of Cnidarians: Hydrozoa –Hydras, hydroids –Polyp dominant Scyphozoa –Jellyfish –Medusa dominant Anthozoa –Sea anemones, corals –No medusa

Fig (a) Colonial polyps (class Hydrozoa) (b) Jellies (class Scyphozoa) Sea wasp (class Cubozoa) (d) Sea anemone (class Anthozoa) (c)

Body of Cnidarians Radial symmetry Hollow sac w/ mouth + surrounding tentacles at 1 end Mouth leads to GV cavity (digestive) Mouth – ingests food, expels waste

Epidermis –Protective covering Gastrodermis –Lines gut, digestive Mesoglea –Gelatinous, acellular –Separates epidermis + gastrodermis

2 body shapes of Cnidarians Polyp –Dorsal mouth w/ tentacles –Hydra Medusa –Mouth on lower oral surface –Jellyfish

Fig Polyp Mouth/anus Body stalk Tentacle Gastrovascular cavity Gastrodermis Mesoglea Epidermis Tentacle Mouth/anus Medusa

Response in Cnidarians Nerve nets –Nerve cells that connect sensory cells in body wall to contractile + gland cells –Cells contacted, entire body responds – crunches in

Feeding in Cnidarians (hydra) Paralyze prey with Nematocysts –Nematocysts Stinging cells (“thread capsules”) In cnidocytes Stimulated – release coiled, hollow thread Sticky OR long and coil around prey OR barbs/spines Prey pushed into mouth GV cavity – digestion –Body motion helps circulate contents

Fig Tentacle Nematocyst “Trigger” Cuticle of prey Thread discharges Thread (coiled) Cnidocyte Thread

Gas exchange/Excretion Diffusion –No cell far from surface

Reproduction in Cnidarians Asexual –Budding – good conditions –Colony – buds remain on parent Sexual –Fall or stagnant water –Become males and females Female – ovary – single egg Male – testis - sperm –Zygote – may become covered with shell for winter

Fig Feeding polyp Reproductive polyp Medusa bud Medusa ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps 1 mm Key Haploid (n) Diploid (2n) Gonad SEXUAL REPRODUCTION MEIOSIS FERTILIZATION Egg Sperm Zygote Planula (larva) Developing polyp Mature polyp

Comb Jellies – Phylum Ctenophora Marine Luminescent 8 rows cilia (comb) 2 tentacles – no nematocysts – adhesive glue cells Radial symmetry 2 cells layers w/ mesoglea Mouth – food in; 2 anal pores – waste out (other end)

Fig. 33-3d A ctenophore, or comb jelly

Flatworms – Phylum Platyhelminthes Flat, elongated, acoelomate Bilateral symmetry Cephalization –“head” at anterior – moves forward; eyespots 3 germ layers – –ectoderm, mesoderm, endoderm Muscular pharynx –Takes in food – 1 opening mouth

Flatworms cont. Nervous system –Simple brain = 2 mass nerve tissue = ganglia – connect to 2 nerve cords Protonephridia –Osmoregulation, waste disposal Complex reproductive organs No organs for circulation, gas exchange –Diffusion through body wall

Fig. 33-3e Acoel flatworms (LM) 1.5 mm

Fig. 33-3f A marine flatworm

3 classes of Flatworms 1. Turbellaria –Free-living –Planarians – pond Crossed eyes Auricles (“ears”) – locate food Carnivore – mouth, pharynx, GV cavity Reproduction –asexual – splits in 2 –Sexual – hermaphrodite – cross-fertilization

Fig Pharynx Gastrovascular cavity Mouth Eyespots Ganglia Ventral nerve cords

2. Trematoda + Monogenea –Flukes – blood + liver –Parasites –Hooks, suckers – attach to host –Complex reproduction

Fig Human host Motile larva Snail host Ciliated larva Male Female 1 mm

3. Cestoda –Intestinal parasite –Tapeworm – long, flat, ribbon-like –Suckers, hooks on scolex (head) –Body – proglottids (segments) Each proglottid – male and female organs (100,000 eggs) –No mouth/digestive sys. – diffusion –Lacks sense organs

Fig Proglottids with reproductive structures Hooks Sucker Scolex 200 µm