30.1. Evolution and Classification of Animals (p. 584)

Animals are multicellular eukaryotes which can be heterotrophic by ingesting food. (Fig. 30.1) (Table 30.1)
Animals produce heterogametes (eggs and sperm) and follow diplontic life cycle where adults will always be diploid and just gametes are haploid.
General Classification
a. All animals likely started out protozoan ancestor. (Fig. 30.2)
b. About 34 animal phyla but nine phyla contain major animal groups.
c. Invertebrates without backbones comprise almost last phylum Chordata which has mostly vertebrates.
Symmetry is a basis for classification.
a. Could possibly have asymmetry or no basic symmetry.
b. Radial symmetry has animals organized circularly; animals for example cnidaria and echinoderms are relatively inactive or could possibly be sessile, stuck to substrate.
c. Bilateral symmetry forms right and left halves; animals might be more active and move toward head end.
Body Plans
a. May be a sac plan with one opening for an incomplete digestive system.
b. Tube-within-a-tube plan has two openings and complete gastrointestinal system route with specialized parts along tube.
Quantity of Germ Layers
a. Sponges have cellular degree of organization without specialized tissues.
b. Cnidaria have tissue degree of organization with two germ layers, ectoderm and endoderm.
c. Other animals have three germ layers--ectoderm, mesoderm, and endoderm--and have organ amount of organization.
Presence or Deficiency of a True Coelom
a. A genuine coelom can be an internal body cavity lined with mesoderm.
b. Flatworms are solid or acoelomate, "no coelom."
c. Roundworms are pseudocoelomate with partial mesoderm next to body wall.
d. Beyond roundworms, these more derived animals are coelomate.
Coelomates Separated into Two Branches
a. Protostomes are animals that develop mouth at blastopore, invagination of endoderm during embryonic development.
b. Deuterostomes are animals that develop anus at blastopore.
Segmentation
a. Segmentation results from repetition of areas of the body, allowing further specialization and differentiation.
b. Mollusks are nonsegmented; annelids, arthropods, and chordates are segmented.
30.2. Invertebrates Without having a True Coelom (p. 586)
Sponges Have Pores
a. In phylum Porifera with 5,000 species.
b. Some freshwater but mostly sessile marine filter feeders.
c. Multicellular but without specialization; viewed as separate evolutionary line from other animals.
d. Structures
i. Most in the shape of a vase; wall is flattened epidermal cells.
ii. Middle wall layer is semi-fluid matrix, amoeboid cells transport nutrients, produce spicules, and sex cells.
iii. Central cavity has opening called an osculum; body wall is perforated by many pores.
iv. Collar cells seen on inner wall have flagella to cause water to pass through in through pores and out osculum; collar cells also engulf food particles and pass the crooks to amoeboid cells.
e. Reproduce
i. Asexually by budding.
ii. Sexually by releasing sperm and eggs into central cavity; zygote forms ciliated larvae that swims to new location.
f. Regeneration: because of lack of specialization, sponges easily regenerate from broken segments.
g. "Skeletal" Structure
i. Classified on foundation internal skeleton of spicules, needle-shaped protective crystals.
ii. Calcium sponges use calcium carbonate; glass sponges use silica.
iii. Spongin fibers are modified collagen network that offers sponges a spongy texture.
Cnidaria Have Radial Symmetry (p. 588)
a. In phylum Cnidaria with 9,000 species.
b. Tubular and bell-shaped animals mostly of coastal reefs, some in oceanic waters.
c. Only two germ layers, endoderm and ectoderm.
d. Radially symmetrical; any longitudinal cut produces identical halves.
e. Cnidocytes are stinging cells that release nematocysts, long coiled hollow threads which could contain poison; triggered when touched.
f. Two basic body forms:
i. Polyps, such as hydra and hydranths, are generally sessile with mouth directed upward.
ii. Medusae, like jellyfish, have the freedom floating; mouth directed downward.
iii. Probably ancestral cnidaria had both forms; some still alternate generations today. (Fig. 30.4a)
g. Sexual reproduction leads to zygote that forms ciliated planula larvae.
h. Diversity:
i. Sea anemones are solid polyps resembling colorful flowers.
ii. Corals have calcium carbonate skeletons and form coral reefs in shallow waters.
iii. Portuguese man-of-war has gas-filled polyp with other polyps dangling to feed or reproduce.
iv. In jellyfishes, medusa is primary stage and polyp is inconspicuous.
i. Hydras Are Solitary Polyps (Fig. 30.5)
i. Mounted on underwater rocks and plants generally in most lakes and ponds.
ii. Person is small tubular polyp lower than one centimeter long.
iii. Person is dead-end sac; one opening is both mouth and anus.
iv. Outer layer of epidermis comes from ectoderm; inner layer, called gastrodermis, is from endoderm which is capable of contract.
v. Outer ectoderm separated from inner endoderm by jellylike mesoglea.
vi. Circular and longitudinal muscle tissues provide movement; nerve cells form nerve net.
vii. Gastrodermal cells secrete enzymes, absorb nutrients and gases which might be provided by diffusion from gastrovascular cavity.
viii. Hydras reproduce sexually or asexually.
- no medusae, only polyp stage.
- under favorable conditions, hydras produce outgrowths called buds.
- can produce ovary or testis in body wall for sexual reproduction.
- has power to regenerate from small fragment.
Flatworms Are Flat (p. 590)
a. In phylum Platyhelminthes with 13,000 species.
b. Acoelomate with sac body plan.
c. Three germ layers present; mesoderm provides bulk and complexity.
d. Systems: muscles, excretory, digestive, and reproductive organs; lack respiratory and circulatory organs (diffusion is adequate at small size).
e. Grouped into three classes; one free living as well as parasitic.
f. Planaria Are Free-Living (Fig. 30.6) (p. 590)
i. Small black, brown, or colorless flat worms.
ii. Live in water where they go after living or dead organisms.
iii. Rid body of excess water by excretory organ which contains a flame cell with cilia.
iv. Ladder-type nervous organ; small brain with two nerve cords joined by cross-branches.
v. Cephalization: planaria locate sensory "eyespots" to anterior.
vi. Glide by ciliated epidermis on film of mucus.
vii. Pharynx is mouth that sucks in food particles to gastrovascular cavity; undigested wastes also exit through pharynx.
viii. Planaria are hermaphroditic, possessing both female and male organs; generally cross-fertilize; eggs hatch in 2-3 weeks into tiny worms.
ix. Able to regenerate.
g. Parasitic Flatworms Have Lost Features (p. 591)
i. Two parasitic classes include tapeworms and flukes.
ii. No sensory organs concentrated at head; instead built with hooks and suckers to add to host.
iii. Absorbs nutrients from host's intestinal tract; therefore lacks own digestive tract.
iv. Coated by protective glycocalyx, a mucopolysaccharide coating.
v. Energy gives extensive reproductive system.
vi. Some use secondary host to harbor larvae until transmitted to primary host for adult stage to contaminate intestinal tract, bile duct, blood, or lungs.
vii. Schistosomiasis
- Due to blood flukes.
- Within people moving into China and Africa.
- Enters body by penetrating skin. (Fig. 30.7)
viii. Tapeworms
- Have scolex (head) containing hooks and suckers.
- Body segments are long compilation of proglottids, each containing male and female reproductive organs.
- Eggs are released in feces; eggs are eaten by animals and larvae burrow into muscle to encyst.
- Can be acquired by eating poorly cooked beef or pork.
- Larval worms form cyst in meat; digested away from cyst, they put on intestinal wall.