Characteristics of Animals: • Heterotrophic → ingest food (other organisms or nonliving organic material) to obtain

organic nutrients • Multicellular, lacking cell walls → 2 specialized cell types seen only in animals –

muscle & nerve cells • Reproduce sexually with diploid stage usually dominating life cycle:

Upon formation of zygote (fusion of egg & sperm), cleavage (successive mitotic cell division without growth) begins, leading to the formation of a hollow multicellular “ball” or blastula. Blastula then undergoes process of gastrulation – invagination (inward migration) of cells and formation of embryonic germ layers, resulting in a gastrula. *structures of additional note: blastocoel, archenteron, blastopore

• While some animals develop directly from immature stages to adults, others have a sexually immature form (larva) that has morphology, eating habit and habitat distinct from its adult stage. Transition from larva to adult = metamorphosis.

Animals can be grouped according to level of organizational complexity concerning the body (body plan); occurs at 4 levels: 1) Symmetry - Differences in body symmetry

- radial – any imaginary plane (parallel to the body’s central axis) through the body divides the animal into mirror images; possess an oral (top) and aboral (bottom) side, but no head/rear & no left/right.

vs. - bilateral – only one imaginary plane divides the animal into mirror images;

possess dorsal (top/back) & ventral (bottom/belly) side and anterior (head) & posterior (tail) end. Concentration of sensory organs and central nervous system in anterior end of the organism = cephalization.

2) Tissues - Differences in organization of embryonic tissue layers

- Animal embryos form germ layers from which various tissues and organs will arise → ectoderm (gives rise to skin and nerves), mesoderm (muscle and some organs), & endoderm (lining of digestive tract and some organs)

- Animals with only ectoderm and endoderm are diploblastic - Animals with all three are triploblastic

3) Body Cavities - Either present or absent

- Body cavity (fluid-filled space separating digestive tract from outer body wall) = coelom in triploblastic animals

- “true” coelom → cavity forms from tissue derived from mesoderm (coelomates)

- “pseudo”coelom → cavity forms from the blastocoel (pseudocoelomates) - acoelomates lack a body cavity/coelom altogether

Introduction to Animals and the Invertebrates

4) Developmental Mode - protostome development vs. deuterostome development

→ protostome mouth develops from first opening during gastrulation (anus forms from second opening) (Grk → protos = first; stoma = mouth) → deuterostome anus develops from first opening during gastrulation (mouth forms from second opening) (Grk → deuteros = second; stoma = mouth)

Invertebrates are a major division of animals that lack a backbone; major groupings of invertebrates include several important phyla: Phylum Name: Representative Organismal Examples: Porifera Sponges Cnidaria Jellyfishes, anemones, corals Platyhelminthes (Flatworms) Planarians, flukes, tapeworms Nematoda (Roundworms) Soil roundworms, parasitic roundworms (e.g. heartworm) Mollusca Snails, clams, oysters, mussels, squid, octopus Annelida (Segmented worms) Polychaetes, earthworms & leeches Arthropods Arachnids, crustaceans, insects Echinodermata Sea stars, sea urchins Chordata* (does possess Lancelets, tunicates (sea squirts) a few invertebrates) Login and watch the animation – login: txau_dobie password: aisd https://www.brainpop.com/science/diversityoflife/invertebrates/

• - Most of the members of this phylum belong to the subphylum Vertebrata (animals with a backbone) and are NOT part of the representative examples included in the discussion regarding invertebrates

Figure 18.4 No true tissues

Radial symmetry

Ancestral colonial protist

Bilateral symmetry

True tissues

Protostom

es

Eum

etazoans Bilaterians

Deuterostom

es

Sponges

Cnidarians

Flatworms

Nematodes

Annelids

Arthropods

Molluscs

Echinoderms

Chordates

Phylum Porifera (pori = pore/hole; fera = bearing) Characteristics: -lack any true tissues or body plan -asymmetrical -sessile (immobile; fixed/attached to one place) -filter-feeders Login and watch the animation – login: txau_dobie password: aisd https://www.brainpop.com/science/diversityoflife/sponges/ Phylum Cnidaria (cnida/knide = nettle) Characteristics: -diploblastic (have only 2 embryonic tissues à ectoderm that becomes outer epidermis & endoderm that becomes inner lining to digestive cavity) -radial symmetry -incomplete digestive cavity (sac body plan) -protostomes -acoelomates -possess cnidocytes (stinging cells for which the phylum is named) -2 forms in their life cycle à polyp (attached) & medusa (free swimming/floating)

Login and watch the animation – login: txau_dobie password: aisd https://www.brainpop.com/science/diversityoflife/cnidarians/ Phylum Platyhelminthes (platy = flat; helminth = worm) Characteristics: -triploblastic (have 3 embryonic tissues) -bilateral symmetry -incomplete digestive cavity (sac body plan) -protostomes -acoelomates

Phylum Nematoda (nemat = thread; odes = like) Characteristics: -triploblastic (have 3 embryonic tissues) -bilateral symmetry -complete digestive cavity (tube-within-a-tube body plan) -protostomes -pseudocoelomates -round, non-segmented

Phylum Molluscs (molluscus = soft) Characteristics: -triploblastic (have 3 embryonic tissues) -bilateral symmetry -complete digestive cavity (tube-within-a-tube body plan) -protostomes -coelomates -possess foot (locomotion), visceral mass (contains internal organs), and mantle (may secrete a shell) -includes several noteworthy classes: gastropoda (gastro = stomach; pod = foot) – Ex: snails cephalopoda (cephalo = head; pod = foot) – Ex: squids, octopuses, cuttlefish bivalvia (bi = two; valvia = hinged shell) – Ex: clams, oysters, mussels Login and watch the animation – login: txau_dobie password: aisd https://www.brainpop.com/science/diversityoflife/mollusks/ Phylum Annelida (anulus = little ring) Characteristics: -triploblastic (have 3 embryonic tissues) -bilateral symmetry -complete digestive cavity (tube-within-a-tube body plan) -protostomes -coelomates -round, segmented Phylum Arthropoda (arthro = joint; pod = foot) Characteristics: -triploblastic (have 3 embryonic tissues) -bilateral symmetry -complete digestive cavity (tube-within-a-tube body plan) -protostomes -coelomates -segmented -exoskeleton made of chitin -jointed appendages -includes several the noteworthy subphyla of Crustacea and Chelicerata as well as the classes of: arachnida - https://www.brainpop.com/science/diversityoflife/arachnids/ insecta - https://www.brainpop.com/science/diversityoflife/insects/ diplopoda (millipedes) & chilopoda (centipedes) Phylum Echinodermata (echino = spiny; derma = skin) Characteristics: -triploblastic (have 3 embryonic tissues) -penta-radial symmetry -complete digestive cavity (tube-within-a-tube body plan) -deuterostomes -coelomates -segmented -endoskeleton -water vascular system with tube feet